EFFECI'S OF SAND BURIAL AND MOVEMENT ON ROCKY INTERTIDAL BENCH COMMUNITIES IN CENTRAL CALIFORNIA
A thesis submitted to the faculty of San Francisco State University
and Moss Landing Marine Laboratories
in partial fulfillment of the requirements for the
degree
Master of Science In
Marine Sciences
by
Carolyn Kathryn Bretz
Moss Landing, California
1995
EFFECTS OF SAND BURIAL AND MOVEMENT ON ROCKY INTERTIDAL BENCH COMMUNITIES IN CENTRAL CALIFORNIA
Carolyn Kathryn Bretz
San Francisco State University
1995
ABSTRACT
Sand burial may play an important role in determining the local, small scale distribution
and abundance of many rocky intertidal species at Waddell Bluffs and Scott Creek. The
purpose of this research was to explore the role of natural sand accumulation in structuring
benthic algal and sessile invertebrate communities within a system seemingly dominated by
this physical disturbance. Intertidal assemblages were influenced by a seasonally recurring
gradient of sediment burial resulting in temporal and spatial heterogeneity. The mosaic
patterns produced were responses to different microhabitats and intercommunity
successional stages created by seasonal disturbance. Seasonal surveys showed areas with
heaviest sediment deposition harbored a mixture of fleshy brown (Pelvetia fastigiata) and
red (Mastocarpus papillatus, Mastocarpus jardinii and Mazzaella splendens) algae, and
extremely low densities of grazing invertebrates, possibly due to their intolerance to
prolonged burial. The green algae, Ulva sp. dominated sites where sand burial was
intermediate. Marine invertebrates were still rare at intermediate sites. Sand covered both
of these assemblages most of the year. The third major assemblage was formed by the
filamentous red alga, Polysiphonia pacifica, which encompassed areas with low, but
persistent sand cover (never more than 5-10 em thick). Other areas with low sand cover
Ill
were dominated by the anemone, A11tlwpleura elegantissima, and the sand tolerant alga,
Neorlwdomela larix.
Experimental clearings created in each algal assemblage were colonized by the common
algal species surrounding each 1 m2 patch, suggesting that either dispersal was limited or
colonizers were influenced strongly by local habitat characteristics. Recolonization by
limited dispersal in sand-swept habitats could explain these results. These hypotheses were
tested partially in reciprocal transplants of Mastocarpus papillatus and Polysiplwnia pacifiCa
which showed differential survival with varied sand burial depths. M. papillatus persisted
under deep sediment burial for significantly (p<.OS) longer periods than P. pacifica. Cover
of the latter decreased more than 77% after a few weeks of thick sand cover.
These results generally suggest that biotic patterns of distribution and abundance in
sand-impacted areas are influenced by species-specific adaptation to the intensity of
sediment disturbance (e.g. duration and depth of sediment cover) and opportunistic life
histories. Results reported here support the notion that persistent mosaic patterns arise
from species responses to small scale environmental heterogeneity (Whittaker and Levin
1977).
Key words: algae; anemone; California; community structure; disturbance; microhabitat;
mosaic; persistence; rocky intertidal; sand scour; sediment inundation; tolerance
I certify that the Abstract above is a correct representation of the content of the thesis.
Thesis Advisor Date
IV
ACKNOWLEDGMENTS
Alt/wugh nature begins with the cause and. ends with the experience, we must follow the opposite course, to begin with experience and by the mea/IS of it investigate the cause.
Leonardo da Vinci
This thesis went to hell and back. It only seems fitting to thank those that made the
journey with me. Through coursework and discussions, I have received a great deal of
scientific advice and wisdom from my committee members Drs. Michael Foster, James
Barry, and John Oliver. For this I am grateful. Many thanks to Dr. Thomas Niesen who
took time from his hectic schedule to read my thesis and participate as a committee member.
A significant part of my career at Moss Landing Marine Labs was inspired by John Oliver.
John has always encouraged me to follow the rules of science, but to have fun doing it. I
am grateful he took the time to support my interest in pursuing too many projects.
I am eternally grateful to the many friends that rode with me through the best and
worst times. Thanks to those that assisted me in the field and lab, especially Ken Israel,
Cassandra Roberts, Mary Nishimoto, Mike McNulty, Dahnmit McHue, and Gina Crane.
Thanks also to my very supportive friends Diana Steller, Nicole Crane, Sandy Yarbrough
and Sandi O'Neil; and Dr. Andrew DeVogelaere who had a fresh perspective and always
provided a chuckle.
My graduate career would not have been possible without the love and support of
some very special people. I owe alot to my parents, whose avid interest in nature and the
scientific world was an impetus for my own love of science. Special admiration and
respect go to Jim Barry who not only gave unlimited scientific guidance, but was a
personal inspiration in many, many ways.
This work was supported, in part, by a grant from the California Department of
Transportation.
v
TABLE OF CONTENTS
LIST OFT ABLES ............................................................................ viii
LIST OFF1GURES .......................................................................... x
INTRODUCTION ............................................................................ 1
METHODS AND TECHNIQUES .......................................................... 5
Study Site ........................................................................... 5
Intertidal Survey Stations ......................................................... 5
Physical Environment ............................................................. 6
Species Composition and Cover ................................................. 6
Field Experiments .................................................................. 8
Artificial Clearing ................................................................ 8
Transplant Experiment .......................................................... 9
Statistical Analyses ................................................................. 10
RESULTS ...................................................................................... 12
Species Composition in Intertidal Mosaic ....................................... 12
Sediment Influence on Species Composition and Cover ...................... 13
Clearing Experiments .............................................................. 14
Reciprocal Transplants ............................................................ 16
Herbivore Densities ................................................................ 17
D!SCUSSION ................................................................................. 19
General Patterns .................................................................... 19
Assemblage Patterns ............................................................... 21
Algal Translocation ................................................................ 25
vi
Clearing Experiment ............................................................... 27
Benthic Invertebrates .............................................................. 30
Rocky Shore-Sandy Beach Ecotone ............................................. 31
LITERATURE CITED ....................................................................... 34
vii
LIST OF TABLES
Table Page
1. Time table showing duration of ol:iservations and experiments ...................... .41
2. Summary of sand deposition at rocky intertidal stations from Waddell Bluffs
and Scott Creek based on monthly samples for 14 months (July 1988 to August
1989). Assemblage type was named for the dominant species characterizing that
station. !=artificially armored shoreline. nd=no data .................................. .43
3. Colonization of algal removal plots in the Ulva, Polysiphonia and Red-Brown
Algal habitat Plots were cleared February 1, 1990 and sampled periodically
until AprilS, April 29 and May 13, respectively. Each data point represents the
mean (±1 SE) of 4-6 plots. Entero-diatom refers to an Enteromorphal
filamentous diatom mix found in the shallow depressions of the rocky bench.
Arrow indicates date of initial clearing .................................................. .4S
4. Single factor analysis of variance (ANOV A) results are shown for seasonal
sand depth versus assemblage (n=14). Student-Neuman-Keuls (SNK) test was
used for pairwise multiple comparisons (Zar 1984). *p<O.OS, ns=non
significant (p>O.OS) ....................................................................... .47
Sa. Results of reciprocal transplant experiments. Data are the mean number (±SE)
of thalli and percent cover of transplants over time for Mastocarpus and
Polysiplwnia, respectively. Comparison of transplants with a cleared border
and non-border are shown. In the field, transplants were marked with coded
PVC to indicate patch type (Mastocarpus {M} or Polysiplwnia {P}), treatment
replicate number (1-S), and treatment type (species and border). Categories for
qualitative observations of unmanipulated plants within recipient patches are as
follows: no change (NC), healthy appearance(+), tissue loss(-), disintegrated
(D), orange, white or bleached appearance (B), gone (0) ........................... .49
Sb. Results of reciprocal transplant experiments. Data are mean sand depth over
time in recipient patches (n=IO). Measurements were made at3, 12, and 2S
weeks ........................................................................................ Sl
viii
6a. Single factor analysis of variance (ANOVA) results are shown for transplant
experiment recipient site (n=6) versus treatment border (n=3). ANOVA results
demonstrating significance were analyzed with Student-Neuman-Keuls (SNK)
test for multiple comparisons (Zar 1984). *p<O.OS, **p<O.Ol, ns=non
significant (p>O.OS) ........................................................................ 53
6b. Repeated measures ANOVAs {model Ill} were used on pooled data to detect
differences in transplant border effect over time. AN OVA results demonstrating
significance were analyzed with Student-Neuman-Keuls (SNK) test for multiple
comparisons (Zar 1984). *p<O.OS, **p<O.Ol, ns=non significant (p>0.05) ..... .55
7. Relative abundance (per m2) of benthic invertebrates living in rocky intertidal
habitats with and without seasonal sand cover. Quadrats (0.10m2) were
sampled at random locations along 50m horizontal transects at 3 elevations ranging
from -0.1 to 2.5m. Areas were sampled in summer and winter of 1990. Numbers
indicate mean and ±1 stnndard deviation (n=60). *Balanus glandula are recorded as
percent cover and are not included in the category All Species ....................... 57
8. Seasonal differences in invertebrate density were analyzed with two-tniled
independent t-tests between selected seasons, habitnts and sites (n=60).
*p<O.OS, **p<O.Ol, ***p<0.001, ns=non significant (p>0.05) .................... 59
9. Grain size analysis of sediment from algal habitnts and Waddell Creek beach.
Values indicate percentnges from totnl size distribution or sorting value. Bolded
values indicate dominant grain sizes. Sediment class size divisions are: coarse
grain= 2.0-1.0 mm, medium grain= 0.354-0.177 mm, fine grain= 0.125-0.088
mm, and silt= <0.088 mm. N=3. Silty sediment was <1% for both seasons at
all areas ...................................................................................... 61
IX
LIST OF FIGURES
Figure Page
1. Map of permanent sampling stations"at Waddell Bluffs and Scott Creek in central
California. Numbers indicate station reference markers on rocky shale bench
outlines ...................................................................................... 63
2. Winter (top) and summer (bottom) cover of beach sand over the rocky shale
benches under Waddell Bluffs. Arrows indicate natuml boulder markers ........... 65
3. Field design for the reciprocal tmnsplant experiment. Factors include sand depth
(low, high), and border effect (none, 10 em). Three treatment levels (reciprocal
transplant, reciprocal tmnsplant with a 10 em clearing, and a control translocation)
were used to test the response of tmnsplanted algae to different sand habitats (n=5).
Qualitative "natuml" controls of unmanipulated plants within each recipient patch
were also examined (not shown). Recipient patches (n=6) in high and low sand
habitats dominated by Mastocarpus papil/atus and Polysiplwnia pacifica,
respectively, were chosen mndomly. Percent cover and number of thalli were
measured over a 6 month interval for P. pacifica and M. papillatus,
respectively .................................................................................. 67
4. Seasonal change in sand depth in rock-y intertidal habitats at Waddell Bluffs and
Scott Creek sites. Data were collected monthly for 14 months from May 1988
through August 1989. Each point represents the mean (±1 standard error) of
measurements from random locations (n=10) .......................................... 69
5. Tree diagmm resulting from avemge linkage clustering using Ward Minimum
Variance Method on percent cover data Euclidean distance was used to measure
similarity, demonstmted by clustering of independent stations (and replicates)
into 4 distinct groupings chamcterized by taxonomic relationship. Labels indicate
site (Waddell Bluffs, w, and Scott Creek, s), station number, and replicate number
(1-5) .......................................................................................... 71
6. Percent cover of Viva sp. and sand depth for intertidal sites dominated by Viva sp.
Data were collected monthly from July 1988 through August 1989. Sand depths
X
6. Percent cover of Viva sp. and sand depth for intertidal sites dominated by Ulva sp.
Data were collected monthly from July 1988 through August 1989. Sand depths
and percent algal cover are the mean (±1 standard deviation) of 10 and 5
measurements from random locations, respectively. nd=no data for percentage algal
cover. Note scale change from a, c to b. Areas indicating an unknown percent cover
due to sand are designated with [?~ followed by a dashed line ........................ 73
7. Percent cover (n=5) of brown and red macroalgae and sand depth (n=IO) for
intertidal sites dominated by this mixed assemblage. Only species which held an
average of >5% cover at some sampling date are included. nd=no data for
percentage algal cover ...................................................................... 75
8. Percent cover (n=S) of Polysiphonia pacifica and sand depth (n=10) for
intertidal sites dominated by Polysiphonia .............................................. ??
9. Percent cover (n=5) of Antlwpleura elegantissima and sand depth (n=IO) for
intertidal sites dominated by the sea anemone ........................................... 79
XI
INTRODUCTION
Physical disturbance can be important in providing space for colonization by
opportunistic and late successional species and has been shown to maintain diversity in
some systems by preventing monopolization of space by competitive dominants (Dayton
1971; Connell 1972; Sousa 1984; Pickett 'and White 1985). Disturbances, such as the
seasonal shifting of sand causing frequent episodes of burial and scour in intertidal
habitats, have an enormous, but poorly understood, effect on community development and
organization (Daly and Mathieson 1977; Taylor and Littler 1982; Littler et al. 1983). Daly
and Mathieson ( 1977) found that the microhabitats created by sand disturbance were
difficult, if not impossible, to characterize since they reflected both varying depths of burial
and frequencies of abrasion.
The habitat ecotone between exposed rocky shores and adjacent sandy beaches is an
insufficiently understood environment (Stewart 1983; Dethier 1991). Species living within
this environment must have behavioral and physical attributes that allow them to survive the
constraints of both habitats. In addition to factors such as wave exposure, desiccation,
insolation, predation, and grazing associated with rock)' shores, the biota of sand-swept
rocky habitats must endure additional physical stress from scour and burial by sediments
leading to abrasion and light reduction. Relatively few studies of rocky intertidal systems
have assessed the effects of sediments from adjacent beaches on the structure of
populations and communities (Frank 1965; Dalli 1969; Markham and Newroth 1972;
Markham 1973; Daly and Mathieson 1977; Mathieson 1982; Robles 1982; Littler et al.
1983; D'Antonio 1986; Shaughnessy 1986). Most that have addressed this question have
done so for only a few macroalgae and large grazing invertebrates and have not addressed
whole community patterns and how sand may influence the distribution of all or most
species.
Compared to the many studies on vertical zonation of rocky intertidal biota, little
information is available on factors influencing horizontal patterns, although horizontal
1
gradients are comm·on. Removal of intertidal organisms by seasonal disturbance provides
cleared areas for new recruits and can be important in maintaining a horizontal mosaic of
species on cobble substrates (Davis and Wilce 1987), boulders (Sousa 1979), intertidal
benches (Paine and Levin 1981; Farrell 1989), tidepools (Dethier 1984) and in sediment
(see Thistle 1981 review). According to Whittaker and Levin (1977), a community mosaic
is created as a result of specialized adaptation and/or resilience to particular microhabitat
structure. If the duration and depth of sand cover or other factors vary between habitats,
two or more species may cooccur in the community with each population centered in sites
more favorable for it, thus resulting in community patchiness. The preference of different
species for unique parts of the mosaic thus creates additional potential for cooccurance of
species (see Levin 1974) and may result in the intermingling of subclimax and mature
intertidal communities (Taylor and Littler 1982; littler et a/. 1983). A combination of
physical and biological stresses, at frequencies and intensities dependent upon site
characteristics, will result in environmental quality suitable for some species and unsuitable
for others (Whittaker and Levin 1977; Pickett and White 1985; Farrell 1989). Daly and
Mathieson (1977) suggested that microhabitats may develop in rocky intertidal areas
disturbed by sand which may, ultimately, produce a mosaic pattern of diversity and
abundance of opportunistic annuals and psammophytic species. These patterns may indeed
reflect varying intensities of sand thickness, abrasion, and light exposure as well as
seasonal release from sediment accumulation. D'Antonio (1986) postulated that the relative
abundance of plants in these categories may vary with the depth, duration of cover, and
intensity of the sediment disturbance.
Community mosaics observed at two sites in central California raised questions
about the distribution and cooccurance of saxicolous algae and sessile invertebrates in areas
of seasonal sand accumulation. Initial yearlong observations revealed repetitive temporal
and spatial patterns, indicating the yearly persistence of several intertidal plant and animal
populations. It was not clear whether the persistence of these community mosaic patterns
2
was due to predictable microhabitat variation in seasonal depth distribution, or was a
successional response to varying disturbance. The accessibility of the study sites provided
the opportunity to investigate the response of patches to physical processes, such as sand
burial.
Objectives
Most studies indicating the importance of sediment disturbance to the persistence of
a particular intertidal community structure have investigated the relationship between
disturbance and population structure using percent sediment cover as the primary measure
of disturbance (Markham and Newroth 1972; Markham 1973; Daly and Mathieson 1977;
Littler and Littler 1980; Mathieson 1982; Seapy and Littler 1982; Littler et al. 1983; Hay
1981; D'Antonio 1986; Gibbons 1988). However, the combined effects of both the cover
and depth of sediment may be more indicative of disturbance severity (i.e., an area with
100% cover could have a sediment thickness of 1 em or 100 em). Distribution studies that
included depth as a variable of disturbance have correlated it with the presence or absence
of single species (Frank 1965; Daly and Mathieson 1977; Mathieson 1982; Pineda and
Escofet 1989). The physical characteristics of the Waddell Bluffs and Scott Creek intertidal
(see Study site) presented a unique opportunity for studying the effects of nonuniform sand
burial on a homogeneous rock substrate. The objectives of this investigation were to
evaluate the effects of duration of burial and sediment depth on the local, small scale
distribution of several intertidal algal and invertebrate species at a site on the outer coast of
central California The following specific questions were addressed:
1) What patterns of sediment burial occur at the rock-y intertidal-sandy beach
interface?;
2) How do distribution patterns of intertidal flora and fauna vary with sediment
distribution at this interface?;
3
3) Do patches of various species persist through time; and
4) If so, are these mosaic patterns maintained by individual species' tolerance to
heterogenous microhabitats?
Surveys of intertidal sites provide.;) information on seasonal patterns of sand
movement on and off rocky intertidal benches, and the abundance and distribution of algae
and sessile invertebrates during periods of sand subsidence. Correlations were used to
evaluate the relationship between the depth and duration of sediment cover and floral and
faunal distribution. Community development was monitored after the disturbance and
manipulative field experiments were established to emulate natural sediment disturbance.
4
METHODS AND TECHNIQUES
Study Site
Observations, sampling, and experimental manipulations were made at Waddell
Bluffs (37°06'16 N, 122°17'18 W) and Scott "creek (37°02'31 N, 122°13'56 W), Santa Cruz
County, California (Figure 1). Intertidal study areas at these sites were approximately 600
x 150m and 330 x 250m for Waddell and Scott Creek, respectively.
Waddell Bluffs (Figure 1a) consist of an extremely unstable Franciscan Shale with
highly erodible rocks that are composed of interbedded mudstones and siltstones. As a
result, landsliding is frequent and extensive (Hecht et al. 1973). Sandy beaches and large,
relatively flat shale benches are present in the littoral habitats bordering the bluffs. Sand
moves on and off large sections of the rocky habitat each year (Figure 2). Winter storms
remove sand, exposing the shale benches from the lower to upper intertidal; sand returns
from late spring until fall (Davis and Ethington 1976; Aubrey 1979). Benches may
accumulate as much as 50 centimeters of sand within a 24 hour period. Slight irregular
sediment fluctuations occur throughout the year.
The Scott Creek area (Figure 1b) has a similar stratigraphic composition to Waddell
Bluffs but is less frequently subject to coastal landslides. The physical processes and biota
characterizing the intertidal resemble those at Waddell Bluffs, making it a valuable site for
comparison to the landslide affected site. Large permanent, high-energy beaches occur
south of both areas adjacent to the rock-y terraces.
Intertidal Survey Stations
Sampling strata at Waddell and Scott Creek sites were chosen on the basis of
species composition during winter months. Stations were marked with plastic-capped
stainless steel pipes (visible above the highest sand thickness during summer) fixed to the
substrate with bolts and z-spar epoxy-putty (Kop-CoatMarine Group©, NJ). Percentage cover
5
of all identifiable species and primary cover of sand were monitored monthly from May
1988 to August 1989 and quarterly from August 1989 to March 1991. Several field
experiments were conducted at selected stations (see Experiments). Table 1 indicates the
duration of sampling and experiments.
Physical Environment
Seasonal changes in beach elevation were measured on the permanent and
temporary beaches at Waddell and Scott Creek using standard profiling techniques (Aubrey
1979) at five meter intervals from fixed markers. To assess temporal changes in beach
configuration, survey profile elevations were taken of both permanent and seasonal beaches
at both Waddell and Scott Creek in 1988, 1990, and 1991. Sediment cores (n=3) were
collected randomly during 1991-1992 from permanent stations within biotic assemblage
patches, the seasonal beach at Waddell, and Waddell Creek beach (permanent beach).
Grain size was determined by a dry-shake method of material separation (Krumbein and
Pettijohn 1938) and fractions weighed to the nearest 0.001g. The textural components of
these analyses are shown in Table 9. Accumulation of sand was recorded within patches at
each pennanent station by measuring sand depth above the underlying shale with a marked
steel rod. Ten random depth measurements were taken monthly at each station from 1988
to 1991. Table 21ists sand depth parameters from July 1988 to August 1989 as the mean
depth measurements (n=10) from each sampling month. Yearly and seasonal sand cover
and movement pattern (approach and subsidence) were also documented in photographs
taken from adjacent cliff overlooks of each intertidal study area. Sampling days each
month were determined by the lowest daylight tides.
Species Composition and Cover
Diversity and abundance of dominant macroalgae and sessile invertebrates were
6
measured at seven permanent stations at Waddell Bluffs and three stations at Scott Creek
(Figure 1). Station elevations (fable 2) were measured using a standard theodilite and tide
levels predicted in tide tables. Six randomly placed 0.5m2 quadrats were photographed
monthly at each station, five for analyses and one alternate if needed. Species composition
and cover were determined in the laboratory from analyses of the photoquadrats and field
notes. Photographs were projected on to a uniformly spaced one-hundred point "grid
quadrat" (Foster et al. 1991) and percent cover of species was determined by the
interception of algae or sessile invertebrates and grid points. Since plots rarely contained
more than one layer, these analyses were assumed to estimate accurately the total cover of
algae in plots (Foster et al. 1991). Additionally, percentage cover was assessed in the field
using a one hundred point plexiglass grid, when conditions such as rain, low light, or
standing water layer precluded use of photography. When a deep sand layer was present in
plots, estimates of percentage cover included only the visible, primary layer of biota not
covered by sand. The data from the five quadrats were summed and averaged to yield
estimates of mean cover at each permanent station on each sampling date. Although
permanent stations were selected in a stratified random manner from existing patterns,
primary component (cluster) analyses were used to demonstrate an intertidal mosaic of
patches with distinct composition. Randomized percentage cover based on February 1989,
1990 data (n=5) from selected permanent stations (n=lO) were arranged (clustered)
according to similarity using a Systat© clustering program. Cluster analyses were used to
detect distinct spatial patterns and identify relationships between sites.
Herbivore densities were sampled on sand-influenced and non-sand influenced
rocky benches at the Waddell Bluffs site. I hypothesized that the abundance and diversity
of invertebrate grazers in sand-inf1uenced areas would be less than in areas without
seasonal sand inundation. Non-sand inf1uenced outcrops (protected from deposition by
nearshore pinnacles) were near benches exposed to fluctuating sand levels. Abundance of
invertebrate grazers was quantified in sixty random 10 cm2 quadrats placed along 50 m
7
horizontal transects, parallel to shore, at three separate tidal elevations of @ -O.lm, + 1.4m,
and 2.5m (n=20 quadrats at each elevation) at each area. Placements of horizontal transects
were determined from random points off a single transect running from the upper to lower
intertidal. Data from separate elevations were pooled for analyses, since questions
concerned only species composition, not stratification. Areas were sampled twice, in
August (burial period) 1990 and December (scour period) 1990. Animals were not
excavated in areas with deep sediment (> 10 em) accumulation, but were assumed to be
dead or absent (Daly and Mathieson 1977; Barry 1988; Marshall and McQuaid 1989).
Therefore, these areas were not included in analyses and indicated in results as "nd" (no
data). Barnacle (Balanus glandula) cover was also measured within the above 10 cm2
quadrats using a one-hundred evenly spaced point grid.
Field Experiments
Artificial Clearing
Experimental plots were denuded of plants and animals to document colonization
patterns within different assemblage patches. I proposed that clearings created during a
season other than the scour period may be colonized by species different from those that
recolonize after the natural scour disturbance. Experimental units were 1m2, an area large
enough to avoid marked edge effects (De Vogelaere 1987). Cleared plots were established
in the Polysiphonia pacifica assemblage (n=6), multispecies red and brown algal
assemblage (n=6), and the Ulva sp. assemblage (n=4) at Waddell Bluffs.
Areas were cleared by scraping with a wire brush, then burnt with a propane torch
to eliminate potential regrowth from remaining spores or vegetative material (see Dayton
1971; Emerson and ZecHer 1978; De Vogelaere 1987; Farrell 1989). Plots were marked
permanently with splash zone epoxy-putty and by measured distances to fixed natural
markers. Each treatment was censused bimonthly for percent cover of recruiting algae
using a O.Sm2 one-hundred point plexiglass grid centered in the plots to avoid edge effects.
8
The condition of surrounding species was assessed qualitatively to help in the evaluation of
patch recovery (i.e., death because of treatment stress). Species lists were made of all
organisms surrounding the treatment plots, species removed from the plots (not necessarily
the same), and those which colonized the plots following manipulation. The experiments
ran from February 1990 when there was limited available space to May 1990 when sand
began to accumulate in the plots.
Transplant/ Translocation Experiment
A reciprocal transplant experiment was conducted at Waddell Beach from June
November 1991 to test the relative survivorship of algae under varied levels of sand
deposition. I hypothesized that species representative of high and low sand environments
would have different survivorship if transplanted into the opposite characteristic habitat.
Algae representative of areas with low (Polysiplwnia pacifica) and high (Mastocarpus
papillatus) sediment depth (see Results) were reciprocally transplanted to plots within
marked algal patches (Figure 3). Samples of M. papillatus were transplanted to three areas
characteristic of low sediment inundation, whereas, P. pacifica was transplanted to three
areas characteristic of high sediment deposition. Transplanted algae of both species were
taken from surrogate algal patches with the assumption that all algae of those species were
genetically equivalent within that intertidal site. Plant samples used were also chosen from
surrogate patches that had experienced a similar history of sand exposure. Sites had little
or no sand cover during the initial transplantation period. Transplant areas were marked
with 0.3 m and 1 m lengths of steel rebar; individual transplants were marked with 4 em
pieces of PVC, coded with patch number, replicate, and treatment type. Pieces of shale
rock with attached algae were removed using a chisel, transported to experimental recipient
patches (n=6) in a plastic tub filled with natural seawater, and glued onto the recipient shale
with z-spar splash zone epoxy-putty (Kop-Coat Marine Group, NJ). Algal replicates were of
approximate equal size. Three transplant treatment levels were used, and are identified by
9
the algal species bordering the transplant: transplanted algae of each species (different
border), transplanted algae with a 10 centimeter border to eliminate crowding by other algae
in the recipient patch (cleared border), and translocation controls (movement of algae to a
similar, but foreign, patch of habitat) to test for variability due to physical manipulations
(same border). No replacement controls we~e used; however, natural unmanipulated plants
in each recipient patch were qualitatively examined as additional control treatments.
Transplants were placed randomly, with five replicates of each treatment level in each of the
six randomly selected recipient patches. During the period of sand coverage, sand depths
were measured. Selected transplants, marked with rebar stakes, were periodically
uncovered to determine condition of the plants under continuous burial. Three weeks after
transplanting, one marked transplant from each of the treatments (n=3) was examined in
each recipient patch (n=6), then reburied. At 3 months, the same transplants were
uncovered, in addition to a second marked transplant from each treatment (n=3). At this
time, percent cover of P. pacifica was determined using a circular (embroidery ring) point
quadrat strung with knotted fishing line creating 50 points. M. papillatus thalli> 1 em were
also counted at 3 months. Changes in morphology and color were monitored at each
sampling time as well. The transplants were reburied after these periodic observations.
The experiment ended when the benches/ and plots were naturally uncovered by winter
storms.
Statistical Analyses
Statistical analyses were executed using Mac! ntosh Statview II program and
occasionally by hand using procedures in Winer (1971) and Zar (1984). Initial data were
tested for normality (g-statistic, Zar 1984) and homogeneity of variances (Cochran's test,
Winer 1971). Data violating assumptions were arcsine and log transformed for percent
cover and counts, respectively, to reduce heteroscedasticity and normalize groups.
Transformed data were then retested. Mean sand depth between assemblages were
10
compared using a single factor (assemblage) analysis of variance (ANOVA), followed by
Student-Neuman-Keuls (SNK) multiple comparison test to detect which means were
significantly different
Differences between treatments within recipient patches in transplant experiments
were tested by one-way A]'JOVA. No signi{icant differences were found for either species
within these treatments, so data were pooled between recipient sites and assumptions
retested. Comparisons of M. papillatus survivorship (thallus count) over time were
compared using repeated measures ANOVA on pooled data for the initial (t=O) to three
month sampling interval. P. pacifica transplant data cover were found to deviate slightly
from normality in the three-six month interval, however ANOVA is fairly robust for data
with considerable heterogeneity, as long as all n's are equal (Zar 1984). These data did not
deviate severely from assumptions and repeated measures ANOVA was used for analysis
of initial (t=O) to six month data. SNK tests were used for pairwise comparisons in both
experiments when ANOV As demonstrated statistical significance.
Seasonal differences in mollusc density were analyzed with 2-sample independent t
tests between selected seasons, habitats and sites. Cover of experimentally cleared plots
over time was compared graphically.
11
RESULTS
Sediment accumulated on intertidal benches at Waddell Bluffs and Scott Creek
during late spring and summer throughout the study (Figure 4) by reduced surf and
subsequent shoreward transport of sand. High sand cover persisted until early fall when
large storms moved the sediment into the nearshore environment. The relative accretion
and abatement of beach materials between successive profiles reflected the well-known
seasonal relationship between apparent strength of wave activity and beach erosion and
formation (Shepard 1950; Ingle 1966; and Davis and Ethington 1976). Seasonal
deposition of sediment created a temporary beach in the upper intertidal during summer
months (seasonally ranging from 10.6-6.1 ft above MLLW) which harbored several motile
invertebrate species absent from the site in winter when the beach was absent (unpublished
data). A cobble substrate was exposed during winter months.
Species Composition in Intertidal Mosaics
Assemblages of algae and sessile invertebrates on intertidal benches were
distributed in a mosaic of four well-defined community patches characterized by
Polysiphonia pacifica (Hollenberg); an assemblage containing species of the genus Viva
(hereafter Ulva sp.) including U. taenia/a (Setchell), U. Iobato (Klitz) and U. angus/a
(Setchell & Gardner); Antlwpleura elegantissima (Brandt); or a mixed group of fleshy red
and brown algae (hereafter called Red-Brown) dominated by Mastocarpus papillatus (J.
Agardh) but including Mazzael/a splendens (Setchell & Gardner), Mastocarpus jardinii
(Setchell & Gardner), and Pelvetia Jastigiata (J. Agardh). Cluster analysis revealed the
presence of four distinctive quadrat groups characterized by their cover dominants (Figure
5). The large euclidean distance between main cluster linkages indicated that groupings
were from assemblages that were distinctly dissimilar to one another in total species
composition. Each patch type occurred over a range of tidal elevations (Table 2), but was
significantly related to a distinct pattern along a statistically significant gradient of sand
12
burial and exposure (single factor ANOVA, p<.001; Table 3). Sand depths characterizing
the A. elegantissima and P. pacifica habitats were found not significantly different (q=0.47;
SNK q.os, z=0.96). No strong correlation was found between sand depth and sand cover
at Waddell Bluffs (n=126, r= 0.014) or Scott Creek (n=56, r= 0.138).
Sediment Influence on Species Composition and Cover
Community type changed dramatically over a relatively short spatial gradient with
change in the depth of seasonal burial by sand. Ulva habitats had a maximum of about 70
em of sand and were bare only for a few winter months when they were colonized (Figure
6) by weedy species, especially Ulva sp. and Porphyra sp. (not shown). Visual cover of
Ulva sp. was greatest when sand depth was less than 8 em. Cover was not known when
sand depth exceeded this level (nd). Any measurement of mean algal cover or large
standard deviation in months of high sediment thickness were likely due to depth
measurements taken outside of the percentage cover quadrats (Figure 6). The substrate
was not entirely uniform (Figure 2) and had areas with small boulders and narrow crevices
along the shale benches. Measurements from these areas allowed for a certain amount of
variability. For example, in March 1989, Waddell station 6 had high algal cover (-90%)
and relatively high sand thickness (-12 em). Large standard deviations shown in June,
August, and October 1988 at Scott Creek station 3 indicate a visually patchy algal cover
poking through the deep sand layer. Algal cover prior to seasonal scour, indicated by the
question mark(?), was also unknown. Patterns of Ulva sp. seasonal recovery and decline
were very similar between stations. Average yearly sand depth at Waddell station 6 was
twice the depth of Waddell stations 2 and 8, and Scott Creek station 3 (Table 2).
Patches dominated by fleshy red and brown algae generally had thick sediment
accumulation for most of the year. Rocky substrata within this habitat were exposed
slightly longer than in the Ulva sp. assemblages. Only species with an average of >5%
cover during at least one sampling date were included as species characteristic of the Red-
13
Brown assemblage type. Although Figure 7 shows the summed percentage cover of all
species, M. papillatus was usually >80% of total algal cover. Like the Ulva habitat, highest
visual algal cover occurred when the sediment thickness was low or absent. Mean algal
cover was usually high one month after sediments were removed (station 4 and 5), but
sometimes patchy between replicate plots .(station 5). Pre-scour algal cover (?) was
unknown. Plant cover rarely exceeded an average of 50% before a new layer of sand
accumulated in spring.
The Polysiplwnia and A11tlwpleura habitats had the shallowest and most similar
mean sand depths (differed an average of only 2 em) and persistent sand cover year-round
(Table 2; Figures 8, 9). The sand level in the Polysiplwnia patches had an average range of
depth from 10 to nearly 0 em. Cover of Polysiplwnia sp. decreased when sand depth
exceeded 10 em; thalli became discolored quickly and disintegrated when handled (pers.
obs.). Cover of Polysiplwnia was highly variable but greater than 40% for most of the year
(Figure 8). Reasons for the decline in cover at station 9 (June) is unknown; however, the
Polysiplwnia was replaced by an abundant cover of small Phyllospadix sp.
The Allthopleura habitat also exhibited high seasonal variability in both sediment
depth and anemone cover (Figure 9), and patterns were not as evident as in the other
habitats. A. elegantissima were not found in plots where sand depths exceeded an average
of 9 em (see Discussion). In some surveys, anemone cover was quantitatively low,
although animals may have been covered by elevated sand levels and not counted in quadrat
point contacts. During summer, and occasionally in winter, anemones were commonly
associated with small patches of the psammophyllic (D'Antonio 1986) alga Neorhodomela
larix.
Clearing Experiments
Rates of recovery within experimental clearings varied considerably between the
three assemblage types. In general, the species of algae surrounding cleared plots
14
recolonized the open space rapidly. Surprisingly, cleared plots did not accumulate large
amounts of sand which may affect recruitment. Diatoms and an Enteromorpha-diatom
complex, found only in shallow depressions in the shale rock, invaded Ulva sp. and Red
Brown algal plots (fable 4) immediately following clearing as shown in other studies
(Connell 1972; De Vogelaere 1987; Emerso? and Zedler 1978). Enteromorpha-diatom
cover decreased to nearly 0 in plots after 6 weeks as the abundance other species increased.
No diatoms were observed in plots cleared in Polysiphonia patches.
Ulva sp. colonized cleared space in the Ulva sp. and Polysiplwnia patches within 3
weeks of removal, but became abundant only in plots surrounded by Ulva (fable 4). This
opportunistic alga recruited to plots two weeks after the initial clearing and attained nearly
100% cover after 9 weeks. Polysiplwnia also recruited rapidly to the Ulva sp. clearings,
but percentage cover reached only 8.7% at 2 months, then declined (fable 4).
Polysiplwnia recolonized clearings made within Polysiplwnia habitat after 1.5
months, and reached nearly one hundred percent cover within 4 months. Ulva sp. was
also present in low abundance in these plots. However, as Polysiphonia became
established, Ulva cover decreased (fable 4). These results suggest that facilitative
succession was not an important process in recolonizing manipulated plots within the
Polysiplwnia clearings.
Mastocarpus jardinii (x =12.6%), Mazzaella splendens (9.8%), Mastocarpus
papillatus (49.9%), Fucus gardneri (4.5%) and Pelvetiajastigiata (14.1%) were present in
pre-removal plots in the Red-Brown algal habitat (fable 4). Growth in these plots
resembled a scattered turf of small red blades. The "Petrocelis-stage" of Mastocarpus was
not found in experimental plots at any sampling date. Juvenile brown algae were also
present, but were less abundant throughout sampling periods than reds. Red algae in these
plots, approached a cover of nearly SO% within about 4 months. Mean cover of browns
reached a peak of 13.6% after 3 months. Sand accumulation in plots at this time was <1
em. Percentage cover of unmanipulated, natural adult populations of brown and red algae,
15
especially M. papillatus, was typically similar to that in cleared plots by the end of the
experiment (see Figure 7). Measurements after May 13 were inhibited by sand
accumulation in the plots.
The anemone habitat was not cleared experimentally due to unsuccessful attempts to
remove pedal discs from the rock substrate .• Anemone body tissue also retained enormous
amounts of seawater which made clearing the substrate with the propane torch impossible.
Reciprocal Transplants
The effects of sand on algal survivorship (number of thalli or cover remaining)
were dramatic. Results indicated that Mastocarpus was more tolerant of sand burial up to 3
months (12 weeks), especially at deep depths, than Polysiphonia. Low sand environments
sustained high cover and thallus number for Polysiplwnia and Mastocarpus, respectively.
Comparisons of initial transplants (t=O) with the final sampling (t=6 months) show the
dramatic change in plant abundance in Mastocarpus recipient patches due to localized
seasonal scour (Table Sa). Transplants within Polysiplzonia recipient patches showed only
slight decrease in abundance from initial to final sampling times. Thallus abundance and
percentage cover did not vary significantly between replicate border treatments (ANOVA,
p>.05) between recipient patches (Table 6a) so these data were later pooled in analyses.
Maslocarpus thallus number decreased slightly (x=2.1, sJ3=0.54 at t=3 months)
when transplanted into Polysiphonia (low sand) patches. Despite loss of thalli, plants
appeared healthy and in good condition over time (pers. obs.). Selected transplant controls
of Mastocarpus lost an average of 1.83 (sE=0.31) thalli after 3 months of burial. In
contrast, Mastocarpus transplant controls after 6 months decreased to zero. Mastocarpus
habitats appear to be naturally cleared (see Discussion-Assemblage Pattem) of existing
biota from winter sand scour. There was no significant difference between M. papillatus
transplants with and without bare rock borders (ANOVA, p>.05; Table 6b). This may
indicate that any change in thallus number over time was not due to crowding (intraspecific
16
algal border) or instability (10 em cleared border). Mastocarpus survivorship (98%) of
selected plants was significantly higher than Polysiplwnia under 3 months of deep sediment
burial (up to 64.6 em of sand). Standard errors for transplants in low sand habitats were
high due to the loss of two M. papillatus transplants between the 3 week and 3 month
interval. Plants were not measured betwef;I1 3 and 6 months after burial, therefore their
condition during this interim could not be ascertained.
Polysiplwnia transplanted into control patches showed no significant change in
percentage cover over time. There were statistical differences (F=0.23; p<.05) between
transplants with and without cleared borders at all sampling times. During the 0-3 month
interval, percent cover in control patches decreased 1.8% (sE=0.54). Plant cover decreased
an additional 1.4% (sE=0.41) under 6 months of burial. Selected transplants of
Polysiplwnia (n=6) into high sand environments died quickly after 3 weeks of burial and
cover decreased about 77 percent; sand depths at this time exceeded 23.6 em (Table Sb).
Sand accumulation in transplant plots was consistent with average depths recorded
previously in these habitats (Figure 4). Benches were covered with as much as 64.6 em of
sediment 3 weeks after the transplantation experiments were initiated.
Herbivore Densities
Densities of molluscs and barnacles (Table 7) were extremely low (< 14.5 per m2)
in areas of high sediment accumulation. Species coin position was similar between Waddell
and Scott Creek with the exception of Loltia limatula, which was absent in all Waddell
samples. Average sediment deptl1 at the time of sampling in August was 40.1 em and 0.83
em in December.
There was significant difference in mollusc abundance between winter samples over
all areas (Table 8). The difference in invertebrate density during the summer months was
obviously confounded by the presence of sand. In areas affected by seasonal sand burial,
the intertidal periwinkle, littorina keenae, was found on algal thalli and not on bare rock or
17
sand. These gastropods were significantly more abundant overnll (increase of 24% and
42% for Waddell Beach and Scott Creek sites, respectively) in the winter months when
sand was absent (2-sample independent Hest, p>.05). Other species were not recorded at
sand influenced sites in August, however, these areas were not completely unburied to
assess presence of animals beneath the sand-layer.
Juvenile barnacles recruited to available bare rock in the winter months when the
benches were clear of sediment Mean barnacle cover was greater on benches not affected
by deposited sediment and covered about 28% at the time of sampling (Table 7). Barnacles
were likely absent on sand-influenced sites in the summer months, as suggested by the
absence of adult or large barnacle tests on sand-swept rocks at surveyed sites during sand
subsidence. Winter cover was significantly greater on benches without sand-influence at
Waddell Bluffs (t=8.18, t.os=1.67, p<.OS) and greater on sand-influenced benches at Scott
Creek (t=2.90). The peak brooding season of Balanus glandula in this region (Hines
1978) coincides with the period of minimal sand accumulation at this site. Both juvenile
and adults comprised barnacle cover in non-sand areas.
Mussels were completely absent at sand disturbed sites (pers. obs.). Apparently,
they require several seasons to become established and fully developed
(Stephenson and Stephenson 1977) which would not be possible where disturbance was
frequent.
18
DISCUSSION
General Patterns
The results of this study demonstrate that sand burial may be an important
component in the local, small scale distribution of several species at Waddell Bluffs and
Scott Creek. Variation in i:he mosaic structfire of the intertidal communities studied was
strongly associated with changes in sediment-related parameters. Thus, even though other
biological and physical processes (e.g., competitive interactions, wave exposure, substrate
availability and type, desiccation, insolation, grazing) may have influenced community
structure, effects of sedimentation appeared to predominate over the spatial and temporal
scales relevant to this study. The distinct intertidal mosaic is certainly correlated with a
natural sediment gradient; but the actual effect of sand on assemblage distribution can only
be speculated from the provided data. Littler et al. (1983) also attributed patterns of
distribution and abundance for several intertidal species to varying degrees of seasonal sand
stress as cover; while the persistence of some perennial species have been shown to be a
consequence of adaptation to sediment movement (Stewart 1983). In general, the
distribution of macroalgae and sessile invertebrates was correlated with the intensity of
seasonal sediment accumulation (i.e., depth and duration of sediment burial).
No significant correlations were found between distance from high tide markers and
tidal elevation, or distance and assemblage composition. The lack of correlation between
tidal elevation and mean sand depth (r-=0.018) indicate that areas of high elevation are not
necessarily those with the least amount of sediment accumulation. Littler et al. (1983)
noted a negative correlation between tidal height and percent sand cover of adjacent
sampling sites. In all likelihood, however, patterns of distribution reflect responses to both
elevation and degree of sediment influence.
Community patches had distinct species compositions and were not simply
midpoints along a horizontal gradient of species (e.g., classification analyses, Figure 5).
Although patch persistence was not measured, I did not observe large scale increases or
19
decreases in the borders of patches. Station observations and examination of photographs
from adjacent cliff overlooks show that patches remained relatively constant in size
throughout the study (some as large as 30m2 diameter). Also, species composition within
patches remained seasonally consistent over the several years of this study.
Reduced surf and longshore curr(!nts result in seasonal transport of sand from
adjacent permanent beaches to the rocky terraces at each study area. Nearshore surface
currents along the coast near Davenport run generally from north to south; however,
upwelling, strong local wind patterns and eddies off Aiio Nuevo Point (Schwing et al.
1991) create complex surface currents which occasionally deflect surface water towards the
coast (Griggs 1974) that may promote transport and deposition of sediment into the
intertidal areas. The burial period was temporally consistent from year to year, but the
removal of sand was dependent on the first series of winter storms and was somewhat
variable over successive years.
Several studies have shown decreased biotic diversity associated with sand
influenced rocky intertidal habitat (Stephenson and Stephenson 1972; Daly and Mathieson
1977; Rogers 1990). Species living in this fluctuating habitat must be adapted to
temporally predictable disturbances and take advantage of periods of favorable conditions
(i.e., sand subsidence) for growth and reproduction. uttler et al. (1983) refer to these
habitats as "refuges" for opportunistic and psammophyllic species. Under conditions of
extreme sediment disturbance, communities should be composed mainly of few species and
low diversity overall (Seapy and uttler 1982). Mathieson (1982) found that areas buried
greater than 7-8 months per year had few species. According to Rogers (1990), areas with
heavy sedimentation would have "lower species diversity and percent cover, greater
abundance of forms and species with resistance to sediment smothering, and an upward
shift [in zonation]" relative to those areas of less deposition. Alternate views in subtidal
(Foster 1975) and other intertidal (Sousa 1979; Paine and Levin 1981) habitats associate
sand scour with increased species diversity. At my study sites, the diversity of dominant
20
species was low as opposed to non-sand influenced areas where qualitative observations
indicate greater diversity. Moreover, nearby areas of similar tidal elevation, but protected
from seasonal sand burial, were occupied mainly by algae different from those in sand
influenced sites. These conflicting results in the literature appear related to the scale
observed and the degree in which the effec.ts of sedimentation contribute to the physical
heterogeneity of the habitats studied.
Assemblage Patterns
Variation between mosaic intertidal habitats was examined in order to assess the
association of physical and biological parameters concurrently. Intertidal surveys using
combination methods of visual estimation and photographic documentation have been
shown effective in estimating cover of biota (Meese and Tomich 1992). However, in some
instances, 3-dimensional estimation of biotic cover was impeded by increasing sand cover
at permanent stations ("nd": Figures 6 and 7).
Two opportunistic species dominated habitats characterized by intermediate sand
burial. Ulva sp. colonized bare rock within weeks after it was uncovered. Porphyra sp.
was not very common at sampled stations (pers. obs.), but resulted in underestimation of
the cover of Ulva in photoquadrats when present since it was usually found on top of the
Ulva layer. The short period of exposure in the habitat(- 3 months) presumably prevented
establishment of species that grow slowly. Accumulation of sediments in spring, in all
probability, killed the remaining Ulva. Laboratory analyses of Ulva under 20 em of sand
indicated high to total mortality after 1 month burial (D'Antonio 1986). At station Waddell
2, the dashed line from November to December indicates the unknown cover of Ulva sp.
before the December sampling date (Figure 6). I suspect that even if Ulva sp. cover was
>0% during this time, it is unlikely that the plants would have survived the physical
scouring as sand retreated in winter. There was as much as two months between some
sampling dates, so a longer recruitment period between surveys and subsequent high cover
21
recorded the following month was possible. As stated above, relatively deep sand depth
with high algal cover were due to depth measurements taken outside percent cover
quadrats.
Stations with the Red-Brown algal assemblage experienced longer seasonal bare
substrate exposure than. those with U{va, possibly enabling longer growth and
development, resulting in patches with more species. Abundance of Mazzaella splendens,
Mastocarpus jardinii, Pelvetia fastigiata and Mastocarpus papillatus fluctuated monthly;
however, M. papillatus was greater than so% of the total algal cover at each sampling.
Percentage cover at some sampling dates may have been underestimated due to layering of
some species. M. papillatus is considered the most common and morphologically variable
algal species on the Pacific coast (Abbott and Hollenberg 1976). This phenotypic-plasticity
was evident when comparing non sand-influenced sites to those where sediment was
absent for only 4 to 5 months. Mature Mastocarpus papillatus in sand-influenced areas had
a decreased stature and more bushy appearance compared with nearby plants at non sand
influenced sites (pers. obs.). Mathieson (1982) noted that growth and reproduction of
species in sand-swept environments were limited to periods of sand subsidence.
Mastocarpus papillatus can respond facultatively to environmental conditions by
either asexual (direct-development of haploid carpospores) or sexual reproduction (Zupan
and West 1988). Modes of algal recovery in naturally or artificially cleared sites in this
study were difficult to identify, since it was possible for adjacent populations to have either
mode of reproduction; from sporophyte (crust) to gametophyte or gametophyte to
gametophyte. It is also revealing to note that the Petrocelis-stage of Mastocarpus was not
found at permanent stations. D'Antonio (1986) suggested that intertidal algae reproducing
sexually must recruit during periods when sand is not present and reach a large enough size
to withstand burial. However, sediment scour alone, rather than burial, may prevent
settling of spores or establishment of germlings (Emerson and Zedler 1978). Red algae
have non-motile spores, and plants may be limited in their ability to disperse and colonize
22
open space (Hoffmann and Ugarte 1985; Nigg 1988). Daly and Mathieson (1977) suggest
that incomplete life histories may be an advantage in sandy habitats because they would
ensure continued genetic stability. Other literature suggests that sand coverage may limit
algal recruitment, aiding species that can perennate and grow vegetatively (Mathieson 1982;
D'Antonio 1986; Barry 1988; Amsler et al. !992) or from portions of holdfasts remaining
after sand scour (Markham and Newroth 1972; Markham 1973; Zupan and West 1988).
Studies also suggest that some algae can produce small groups of discoid cells (3-4 cells)
prior to seasonal disturbance, such as sand coverage (Mathieson 1982; Zupan and West
1988; Reed, pers. comm.). These cells may be highly resistant to harsh conditions
produced by prolonged burial (e.g., anoxic sediment layer, reduced light). In this study,
the notion that microscopic cells or tissue survive deep burial is supported by the
appearance of very small thalli of red algae shortly after total sand subsidence in winter. It
is not known whether these recruits originated from previously buried tissue or by the rapid
recruitment of spores from adult plants fringing the area. Moreover, the absence of
Pertocelis sp. further augments the presumption of existing algal cells or tissue. Even early
on, Ulva sp. was never found in areas typically dominated by M. papillatus, and it seems
possible that Ulva sp. recruitment was inhibited by the presence of existing species.
Mastocarpus may use this strategy to outcompete other algae (including Ulva) for space
during sand subsidence. Unfortunately, attempts to evaluate this possibility were
inconclusive.
Plant viability was not examined during periods of burial, so it can only be
suggested from depth of sediment at the time of sampling that mature algae in deeply
sedimented areas were indeed negatively affected or absent due to scour. This exposes one
of the problems using measurements of percentage cover from photoquadrats since, unless
modified, this method does not allow for the evaluation of secondary layering. Because
deep sediment cover obscures algae or other species, the presence or absence of buried
species is unknown and likely underestimated. Failure to excavate and examine plants
23
under heavy summer burial produced the "no data" (nd) shown in Figures 6 and 7. The
viability and reproductive status of these buried plants are essential to evaluate some of the
hypotheses considered. However, even conservative interpretation and results of the
transplant experiments indicate that mortality must have been high under deep sediment
conditions.
Assemblages dominated by Polysiplwnia pacifiCa were typical of areas with low,
but persistent sand cover. This finely branched, turf-forming alga retains sediment,
forming a sediment-algal matrix that may provide greater bed stability (Rawlence and
Taylor 1970; Hay 1981), in addition to creating a more suitable habitat for infaunal
invertebrates. Polysiphonia and Antlwpleura habitats were so similar in their average
sediment depths that the principle factor influencing their distribution may have been
elevation.
Alztlwpleura elegantissima can withstand shallow sand burial by elongation of its
column to extend above the sand layer (Taylor and Littler 1982; Pineda and Escofet 1989).
Studies have shown that the solitary form of A. elegantissima does better in heavily sand
influenced environments and can survive burial >3 months (Sebens 1980). The clonal
form dominated sampling areas of this study. Although clonal aggregation reduces
desiccation stress, it may limit the distribution of the anemones to areas less inundated with
sediments. Clonal anemones are less mobile and tended to be found in areas where sand
levels did not exceed 9 em. They are tolerant to some complete burial (as indicated by
results in Figure 9), but typically at depths shallower and durations less than those shown
during this study. At deeper depths the smaller (clonal form) anemones could not elongate
the column sufficiently to bring the oral disc above the sand surface (Pineda and Escofet
1989). Dayton (1971) tested the hypothesis that desiccation set distributional limits on A.
elegantissima. He transplanted animals outside their range in Puget Sound and found that
animals survived well in winter, but not in spring when low tides moved to daytime hours.
Anemones at Waddell and Scotts Creek did not appear to suffer desiccation stress even
24
though they were subjected to afternoon low tides in winter when there was little or no
sand.
Algal Translocation
Results of the transplant experiment .suggest that Polysiplwnia pacifica is intolerant
of high sediment accumulation and thus its distribution may be restricted to sites with
shallow sediment depths. Survivorship results and observations of Mastocarpus papillatus
suggest that its distribution in the study areas is independent of effects from seasonal
sediment accumulation. Other field transplant studies demonstrate variability in the
tolerance of algae to sediment burial. Markham (1972) transplanted Gymnogongrus
linearis to areas of variable wave exposure and sediment accumulation and found the plants
to be tolerant of heavy sand burial and abrasion. Markham (1973) found also that growth
rate and dominance of Laminaria sinclairii was higher in areas where sand burial was the
greatest. Mathieson (1982) documented high survivorship of Plweostrophion irreulare
transplants in sandy areas, but only if surrounding algae were removed. Transplanting
species into patches of dissimilar species did not significantly affect the translocated algae
(Table 6b) within the duration of this study. The general appearance and morphology of
buried plants that had not been experimentally manipulated were compared to transplant
control plants, but no actual measurements were made of these unmanipulated plants.
These evaluations were especially important for M. papillatus transplants which were
heavily buried (>23 em) after 3 weeks. The undisturbed controls were similar to those of
transplanted algae, so I assumed that the transplanting procedure had minimal negative
effect (Figure 4a). Properly designed controls would have included replacing removed
plants to their original locations. Regardless, plants did not seem to be affected by the
transplant procedure- which the additional controls would have tested. A few M. papillatus
plants appeared slightly bleached or orange after 3 months, but little tissue loss was
apparent.
25
Some species may require particular intensities of disturbance (Paine and Levin
1981) and adaptations to chronic disturbances can occur where species become dependent
on predictable perturbations (Dethier 1984). The persistence of Mastocarpus in areas of
heavy sediment inundation may indicate that plants are tolerant of prolonged burial and
repeated sand abrasion. O'Antonio (1986). tested the tolerance of several macroa!gae to
sand burial in the lab and found a definite gradient among species. Mastocarpus papillatus
plants in her lab experiments survived well under 20 em of sand after 1 month, having only
lost reproductive papillae, but lost nearly all tissue after 3 months. At my sites, loss of M.
papillatus thalli was minimal under >50 em of sand after 3 months. D'Antonio (1986)
suggested also that sand may also be linked to the development and persistence of
Neorhodomela larix, another psammophyllic species. In the field, she found that natural
populations of N.larix suffered little damage and remained reproductive under 40 em burial
after 2 weeks. Survival of transplanted Mastocarpus after 6 months was zero due to the
seasonal scouring of rocky benches (Figure 2). However, data concerning Mastocarpus
survival shown in Table Sa may be somewhat misleading since it is quite possible that
plants were not entirely dead and tiny bits of viable tissue remained on the shale rock (see
Assemblage Patter/IS).
Survivorship was defined in my study as the number of thalli or percentage cover
of plants remaining at subsequent sampling periods. Initial numbers of M. papillatus and
percentage cover of P. pacifica were defined to equal 100% survival. Polysiphonla
transplanted in a similar patch type with a shallow sand layer had high survivorship
throughout the sampling period and did not appear to differ from the in situ (non
transplanted) plants. Higher mortality of P. pacifica transplanted to M. papillatus habitats
with cleared borders versus no border, was likely related to the destabilization of the
sediment-alga! matrix by wave action. Although deep sand layers had no strong anoxic
smell or dark black color during the course of the experiment I assumed that oxygen and
light levels were lower and contributed to decreased survivorship. D'Antonio's (1986)
26
laboratory examination of Cryptosiphonia woodii (morphologically similar to
Polysiplwnia) demonstrated severe reductions in plant tissue after I month under 15-20 em
sand. Nevertheless, her controls indicate that plant reductions may have been due to
transplant procedures.
Subtidal studies have shown that sand burial can have detrimental effects on
gametophytes through reduced light and reduced gas exchange (Devinny and Valse 1978).
Perennial plants growing in this environment must be adapted to extreme reductions in light
intensity. Even a very thin layer of sediment will reduce light penetration. For example,
Shaughnessy (1986) found a decrease in light level from 627 uE m-2 s-1 (surface
irradiance) to 5 uE m-2 s-1 with a 3 mm sand overlay, and to 0 uE m-2 s-1 under 6 mm
depth. Grain size in the Shaughnessy study was very coarse (0.4-0.8 mm) compared to
the finer sediments at Waddell and Scott Creek (Table 9), so I assume there was little or no
light transmittance under any significant cover of sediment (>0.5 mm) in this study.
Clearing Experiment
Experimental clearings have been used in several studies of succession (Emerson
and Zedler 1978; Foster 1975; DeVogelaere 1987; Farrell 1988), species' distribution
(Marks 1974; Denslow 1980; Foster 1982), competitive interactions (Barry 1988; Gill and
Marks 1991), and grazer effects (Robles 1982). Clearing experiments were employed to
determine if mosaic patterns reflected reproductive time scale (i.e., spore availability) or
tolerance to sediment-related disturbance. I hypothesized that Ulva sp. would colonize
most or all cleared plots, thus dominate initially during any successional sequence,
regardless of the timing of a disturbance. Results in this study indicated that recovery by
dominant species was rapid during the season clearings were created, but not predictably
limited to early successional species. Littler et al. (1983) also recorded rapid recovery of
plots cleared during winter, and noted that predominant species recovered within 5-6
months. Artificial clearings created during different seasons can lead to different sequences
27
of algal colonizers (Emerson and Zedler 1978; Denslow 1980). Vlva sp. in this study
recolonized available space as the primary successional stage as shown in other
colonization studies (Sousa 1979; Littler 1979; Davis and Wilce 1987; De Vogelaere 1987;
Foster et ai. 1988; Farrell 1989). Viva sp. even recolonized clearings in the Red-Brown
algal patches, although Viva sp. was never found in these areas during previous surveys.
Previous studies by Connell ( 1972) and Sousa (1984) reported that succession proceeds
from bacteria and diatoms to ephemeral green algae, and finally to perennial algae (usually
reds and browns), which persist following colonization. In my clearings diatoms were
present in low abundance. Primary colonizers varied from plot to plot, and there is little
evidence that any of the dominant algae at the sites required the presence of another species
for establishment Connell (1972) suggested that changes result from different breeding
seasons, differential motility of spores, and/or different growth rates. Therefore, failure of
an alga to recolonize a plot after clearing, may be related to the lack of propagules due to the
timing of the reproductive season, even if it was present initially. Some algae may colonize
exposed areas quickly because the surrounding undisturbed area is a source of recruits for
those species (Sousa 1979; Denslow 1980; DeVogelaere 1987). It is also possible that
species rejuvenated from spores that persisted because of insufficient burning techniques.
Emerson and Zedler (1978) noted that the initial invasion by diatoms was followed by
colonization of Enteromorpha flexnosa and Vlva rig ida 2 weeks after disturbance, similar
to my plots cleared in winter. In Polysiplwnia-removai plots (Table 4), Vlva showed a
decline following its peak abundance on March 9, which suggests an inability to maintain
dominance in a site once another species (Polysiphonia) became established. As reds
became dominant in some plots (Table 4), they in turn may have inhibited the reinvasion by
early successional species (Emerson and Zedler 1978). I'm not convinced, however, that
the decline of the Enteromorpha-diatom complex was due to increase of other algae, since it
was invariably restricted to shallow depressions of the rocky benches. Desiccation may
have been the controlling factor for its later absence.
28
The dispersal range for adult red and brown algae, common to late successional
stages, (Dayton 1973; Sousa 1984) may have had a strong affect on offspring recruitment
to experimental patches. Results indicated that the recovery of experimentally cleared plots
was similar to the dominant algae surrounding each plot. However, at the early stages of
recovery juvenile red and brown algae were .difficult to identify accurately. In this study,
the huge standard error in algal cover (Table 4) indicates patchy recruitment to the clearings
and variability between replicate plots. Colonization in these sediment disturbed areas may
have been influenced strongly by the local availability of propagules and, perhaps, by the
short dispersal ranges of spores. Sousa (1984) related short distance dispersal of
propagules to high abundance of recruits (demonstrated by percent cover of juveniles)
surrounded by high numbers of adult plants. Contrary to this idea, DeAngelis et al. (1979)
noted that recovery of a patch from a nearby spore source was independent of the actual
size of the source patch and was dependent only on the fact that the species existed in the
source patch. If spore dispersal is limited to short distances, as some literature suggests,
then the rapid colonization of red and brown algae to plots would indicate that the
surrounding adults were reproductive at the time of experimental clearing. These results, in
turn, echo other studies (Daly and Mathieson 1977; D'Antonio 1986; Rogers 1990)
indicating that species in areas with temporally predictable disturbances (i.e., seasonal)
should have rapid recruitment and growth. In Red-Brown algal plots, clearings were made
in late winter. Because M. papillatus is reproductive all year with a winter peak (Northcraft
1948), spores were available for recolonization of cleared plots. M. papillntus and the
fucoid Pelvetiopsis have been shown to appear first in plots cleared during winter. In
central California, Sousa (1984) found that M. papillatus reached about 6% cover 2 months
after clearing. Pelvetia fastigiata is reproductive from winter through spring (Gunnill
1980), while Mazzaelln splendens has perennial holdfasts and annual blades. Blades grow
in late winter, reach maximum size in mid-summer, and reproduce and senesce during fall
(Foster et al. 1988). M. splendens was less common at the tidal elevations of the
29
permanent stations, and would be less likely to recolonize cleared plots. Although the
reproductive status of adults surrounding the plots was not determined, proximity of spore
sources in known to affect recruitment patterns of intertidal algae (Dayton 1973; DeAngelis
et al. 1979; Sousa 1979; Denslow 1980; Sousa 1984; DeVogelaere 1987) and is
undoubtedly important in this study.
Although clearings in the anemone patch type were unfortunately not possible, it
has been documented that removal of A. elegantissima beds provides space for algal
recruits (Taylor and Littler 1982). Apparently, algae associated with anemone beds are
dependent on the beds water-retaining capabilities, and decrease when anemone patches are
removed. Although patches of anemones are commonly associated with sediments,
recruitment to available space by Allllwpleura can be inhibited by sediment abrasion (Barry
1988).
Benthic Invertebrates
Sand accumulation plays an important role in the distribution and abundance of
benthic invertebrates at the surveyed sites. Species diversity on rocky benches without
seasonal sand burial of this study was not as high as that reported for similar habitats.
!Jttler et al. ( 1983) reported that Tegula jwzebralis, Collisela scabra, Lottia gigantea, and
Alztlwpleura elegantissima inhabited areas with minimal (<8.8%) sand cover. Although T.
fimebralis migrates away from heavy sediment deposition (!Jttler et al. 1983; D'Antonio
1986), it is known to be a sand-tolerant species which commonly occurs in clonal
aggregations of Antlwpleura elegalllissima (Francis 1973). T. fimebralis was not found in
sand-influenced areas in this study, although it was the dominant gastropod in nearby
similar habitats without seasonal sand cover (Table 7). The mossy chiton Mopalia mucosa,
and marine polychaetes Phragmatopoma califomica and Sabellaria sp. are also tolerant of
moderate sand burial (Francis 1973), but were absent from sand-stressed areas. The
gastropod l.ittorina keenae accounted for 42% of the molluscan grazers in non-sand areas
30
and 100% in sand-impacted areas (Table 7). L. keenae was the only grazer present at all
sites in the winter and found strictly on Neorhodomela larix and Polysiplwnia pacifica
plants. Five of the 9 numerically dominant invertebrates counted at all sites were limpets.
A laboratory study by Barry (1988) showed mortality oflimpets and chi tons buried in 2 em
of sand to be 100% after 5 days. Marshall i).lld McQuaid (1989) also found that patellid
limpets did not survive more than 3 days under 15 em of sand due to reduced oxygen
tension. The absence of benthic invertebrates at any sand-influenced station suggests their
intense intolerance even moderate sand accumulation. However, as previously noted, areas
with elevated sand levels were not cleared to determine the presence of live animals beneath
sediments. The relative lack of grazers in my results also indicates that herbivory exerted
little or no influence on the structure of the algal community of these sand-influenced
habitats. However, it is important to note that completely different invertebrate
communities may exist at these sites during high tide, and that these communities may be
influencing algal community patterns.
Sand may have a negative effect on the larval or juvenile stages of invertebrates,
and may dramatically inhibit recruitment in habitats that accumulate a sediment layer
(D'Antonio 1986; Barry 1988). The presence of young barnacles at Waddell and Scott
Creek (Table 5) suggests that although the potential for recruitment may be high, the sand
disturbance inhibits settlement or results in high juvenile mortality or both. The presence of
sand in the intertidal can also modify vertical zonation and the distribution of some
barnacles and mussels has been set by the physical smothering action of sand (Littler 1983)
rather than by biological factors. Frank (1966), Daly and Mathieson (1977), and Littler
(1983) have also noted that the lower limits of limpets, mussels and barnacles have been set
by the seasonal level of sand burial.
Rocky Shore-Sandy Beach Ecotone
Results of my study provide some additional insight into the association between intertidal
31
community mosaics and sand burial. Although direct evidence of the influence of sand on
biotic distribution is limited in this and other studies, and many conclusions about its affect
on community structure are speculative; these data effectively illustrate the attributes
comprised by inhabitants of areas disturbed by seasonal sedimentation. Species within
sand-swept rocky intertidal. environments cap be defined as ruderal strategists or species
adapted to make use of disturbed habitats (Grime 1977). Plants and animals in sand
impacted habitats must have adaptations, such as abrasion-resistant morphologies,
opportunistic life histories, and rapid growth that allow them to outcompete other species
for resources in these areas. Results of experimental clearings and natural seasonal patterns
support these notions, where opportunistic and, seemingly, psammophyllic species
dominated. Opportunistic forms have been defined as rapid colonizers, ephemerals, or
perennials with vegetative short-cuts to their life history. However, some species
considered to be late successional, (e.g., red and brown algae), have young thalli
possessing characteristics that parallel opportunistic forms (e.g., Mastocarpus papillatus:
Littler and Littler 1980). Persistence of these communities require specialized growth and
morphological characteristics and/or reproductive patterns that allow recolonization
following seasonal disturbance by sand inundation. The rapid appearance of small red
thalli in study areas following seasonal sand subsidence suggests that these habitats may be
occupied by algal species which utilize an asexual (vegetative) form of colonization. Patch
occupancy will be detem1ined at least initially over ecological time scales by the season of
disturbance [birth of the space] and the local availability of propagules (Paine and Levin
1981). The reverse, that reproductive strategy and season are determined by the probability
of space being available for recruitment (Whittaker and Levin 1977; Emerson and Zedler
1978; Sousa 1979; Littler et al. 1980; Hoffmann and Ugarte 1985), also appears to be true
and likely develops over evolutionary time scales. In habitats studied here, the ability to
dominate areas where other species cannot tolerate the intensity of the disturbance can be
quite beneficial. Perhaps this is supported, in part, by the results of reciprocal transplant
32
experiment where high survival was determined by position within the sediment gradient.
Species' persistence may be controlled by both limited dispersal (short-term) and tolerance
to burial depth creating different microhabitat characteristics (long-term). Daly and
Mathieson (1977) suggest that the historical sequences of sand inundation determine the
zonation of species, and that reproduction and growth are necessarily synchronized with
seasonal sediment subsidence. Do the distributional patterns of biota in this study reflect
the response of species to variation in sediment distribution? Although speculative, a
simple answer may be, if microhabitats differ in physical properties, such as sand depth,
then sand can define the areas in which the microhabitats, and subsequent associated biota,
may be dispersed. Variation in sediment depth differs according to microhabitat variation
in physical processes, leading to physically defined patch boundaries that are later occupied
(e.g., colonized and/or tolerated) by appropriate species.
33
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39
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40
Table 1 Time table showing duration of observations and experiments.
41
SEDihfENT DEPTH • D B a B
I I
R I .I ALGAUANB.fONE COVER .I I
I .jO>. BEAG! INFAUNALCORES m • a • 1-J pilot 1 I I CLEARING EXPERIMENT
-~- I .I BEACH PRORLES I I I I I
r GRAIN SIZE ANALYSES
I I B
REOPROCALTRANSPLANT
J A J 0 J A J 0 J A J 0 J A J 0 J A J 0 J A J 0
1987 1988 1989 1990 1991 1992
Table 2 Summary of sand deposition at rocky intertidal stations from Waddell
Bluffs and Scott Creek based on monthly samples for 14 months (July 1988 to August 1989). Assemblage type was named for the dominant species characterizing that station. nd=no data.
43
Sand measurements
Station Distance to Elevation mean sand Std. rum~. min. percent Std. ma"'c rum. months
~ IlQ. shore (m) (ml assemblaoc type n depth fcml D.!;L ...d£J2lh ...d£J2lh £Q.Y.tl D.!;L %cover %cover w/o sand
Waddell Bluffs 70.7 0.7 A. elegantissima 14 3.1 1.3 9.2 0.9 4.8 3.8 15.2 0.0 0 2 42.0 -0.2 U/va sp. 14 24.8 2.5 65.7 0.4 30.1 17.9 100.0 0.0 2 6 53.6 1.0 Ulva sp. 12 54.8 5.1 76.3 0.0 58.4 13.1 100.0 0.0 3 3 54.5 0.2 ?.pacifica 14 4.0 1.2 12.7 1.0 63.3 14.7 88.8 16.0 0 9 0.7 P. pacifica 14 2.0 0.6 6.3 0.9 53.1 8.8 100.0 5.6 0 4 55.5 1.3 Brown and Red algae 14 35.0 3.7 82.3 0.0 50.6 6.8 100.0 0.0 4 5 59.1 0.6 Brown and Red algae 14 38.3 6.2 101.5 0.0 51.8 25.9 100.0 0.0 4
Scott.<; Creek 2 nd 0.3 P. pacifica 14 2.8 1.3 10.2 0.5 23.1 12.8 47.1 7.6 0 3 nd 0.6 Ulva sp. 14 28.1 2.3 49.8 0.3 31.1 14.6 71.2 0.8 4 4 nd 0.2 A. elegantissima 14 2.0 1.0 6.8 0.7 24.2 6.5 100.0 2.8 0
Table 3 Single factor analysis of vmiance (ANOVA) results are shown for seasonal
sand depth versus assemblage (n=14). Student-Neuman-Keuls (SNK) test was used for pairwise multiple comparisons (Zar 1984). *p<0.05, ns=non significant (p>0.05) ..
45
Source
Total Assemblage Error
DEPTH VS ASSEMBLAGE
AN OVA
df
55
MS F p Comparison
561.980 10.635 0.001 mi.xed>Ulva* 3 3917.610
52 368.380 mixed>Polysiphonia* Ulva>Polysiphonia* Polysiphonia~Antlzopleura
Table 4 Colonization of algal removal plots in the Ulva, Polysiphonia and Red
Brown Algal habitat. Plots were cleared February 1, 1990 and sampled periodically until April 5, April 29 and May 13, respectively. Each data point represents the mean cover (±1 SE) of 4-6 plots. Entero-diatom refers to an Enteromorphal filamentous diatom mix found in the shallow depressions of the rocky bench.
47
Date Febl Feb 8 Feb22 Mar9 Mar23 Apr5 Apr29 MayS I May 13 Cleared plot n (initial)
IDva sp. 4 Ulva 98 ±1.7 1.6 ±21 14 ±5.7 42 ±15.9 86 ±21.1 100- 100- 100-Polysiphonia pacifica 1.5 ±23 2.3 ±3.8 8.7 ±5.7 4.7 ±5.3 0 Entero-diatom 2.5 ±0.7 8.7 ±5.2 1.0 ±2.2 0.3 ±1.6 0 . diatoms 8.5 ±20.8 0
Polysiphonia 6 Uh•a 0.7 ±1.5 1.2 ±1.4 4.5 ±3.7 3.7 ±3.7 0.8 ±1.6 0.2 ±0.9 0.1 ±1.1 0
Polysiphonia pacifica 98 ±5.3 10.0 ±1.1 19.0 ±1.7 45 ±9.7 67 ±10.8 100- 100-
mixed alg!l~ 6 diatoms 8.0 ±4.6 7.5 ±4.3 0.8 ±1.5 0
Entero-diatom 7.0 ±4.3 0 Mastocarpus papillatus 50 ±4.2 Mastocarpusjardinii 13 ±5.3 Pelvetiafastigiata 14 ±3.6
Fucus distichus 4.5 ±10.6 Iridaea splendens 9.8 ±4.0
small red blades 5.8 ±4.6 11 ±5.3 32 ±9.7 34 ±6.6 no data 43.0 ±15.1 juv. browns 4.3 ±3.3 9.1 ±4.6 14 ±4.6 no data 14.1 ±4.3
Table Sa Results of reciprocal transplant experiments. Data are the mean number
(±SE) of thalli and percent cover of transplants over time for Mastocarpus and Polysiplwnia, respectively. Comparison of transplants with a cleared border and nonborder are shown. In the field, transplants were marked with coded PVC to indicate patch type (Mastocarpus {M} or Polysiplwnia {P}), treatment replicate number (1-5), and treatment type (species and border). Catagories for qualitative observations of unmanipulated plants within recipient patches are as follows: no change (NC), healthy appearance(+), tissue loss(-), disintigrated (D), orange, white or bleached appearance (B), gone (G).
49
~ ~Q }3Q[d~( Comrnl Qllalitativ~ r;Qntrnl lG.m~Qlant~Q s12eci~s ~ n (10 em clearing) ~into different sgecies) (into same sgecies) (unmaniEulated E:lants)
[mean± SE)
?.pacifica Ml MZ ll:ll Ml M2 ll:ll fl .E2. £>. fl .E2. £>. percent cover (SE) t=O 5 38.8 (6.2) 43.4 (9.1) 34.6 (6.3) 46.8 (9.7) 35.4 (5.7) 40.0 (10.3) 42.2 (11.6) 46.2 (9.1) 40.2 (10.0)
t=3 8 9 6 10 7 12 32 55 37 + + +
lfl t=l2 2 0 3.5 (0.7) 1.0 (1.4) 3.5 (3.5) 2.5 (3.5) 1.5 (1.2) 35.5 (4.9) 50.5 (6.4) 29.0 (1.4) NC NC NC
0 t=25 5 0 0 0 0 0 0 40.6 (11.1) 45.2 (8.1) 37.4 (9.8) NC NC
M. papilla/us fl .E2. £>. fl .E2. £>. Ml MZ ll:ll Ml MZ ll:ll number of thalli (SE) t=O 5 17.8 (7.8) 17.0 (5.5) 19.6 (5.4) 14.2 (2.9) 16.6 (6.2) 17.2 (5.8) 16.6 (5.5) 14.8 (4.5) 13.8 (3.9)
t=3 9 12 0 11 20 14 15 20 18 + + + t=12 2 14.5 (9.2) 16.0 (5.7) 11.5 (16.3) 13.5 (3.5) 14.5 (6.4) 11.0 (4.2) 17.5 (3.5) 18.0 (2.8) 15.5 (0.7) .+,- .+,B,+ t=25 5 17.0 (4.6) 16.0 (4.6) 15.2 (8.7) 14.2 (2.9) 13.4 (3.6) 14.0 (4.5) 0 0 0 G G G
Table Sb Results of reciprocal transplant experiments. Data are mean sand depth over
time in recipient patches (n=lO). Measurements were made at 3, 12, and 25 weeks.
51
duration of
sampling date sand burial average depth in centimeters (+1SE)
n Ml M2. Ml fl 1:2. N
June 14, 1991 3 weeks 10 38.5 (5.09) 23.6 (4.92) 26.9 (5.77) 6.6 (0.49) 6.7 (1.09) 6.1 (0.24)
lJl August 12, 1991 3 months 10 64.6 (10.46) 54.6 (2.18) 62.6 (8.31) 6.6 (0.23) 7.3 (0.74) 6.5 (0.89), t-.J November 6, 1991 6 months 10 0.65 (0.55) 1.6 (1.58) 0 3.8 (0.16) 5.0 (1.84) 3.2 (0.27)
Table 6a Single factor analysis of variance CANOVA) results are shown for transplant
experiment recipient site (n=6) versus treatmentborder (n=3). AN OVA results demonstrating significance were analyzed with Student-Neuman-Keuls (SNK) test for multiple comparisons (Zar !984). *p<O.OS, ns=non significant (p>0.05).
53
TRANSPLANTEXPER~NTS
SITE VS BORDER ANOVA
Source df MS F p
Sit~ (MJ-M2-M3l cleared 2 33.500 1.779 ns different 2 56.368 2.034 ns control (same) 2 16.037 0.44 OS
Sit~ a:J-E2-E1l cleared 2 0.007 0.283 OS
different 2 0.007 0.38 ns control (same) 2 0.016 0.391 OS
54
Table 6b Repeated measures ANOVAs {model Ill} were used on pooled data to
detect differences in transplant border effect over time. AN OVA results demonstrating significance were analyzed with Student-Neuman-Keuls (SNK) test for multiple comparisons (Zar 1984). *p<0.05, **p<O.Ol, ns=non significant (p>0.05).
55
TIME VS BORDER REPEATED MEASURES ANOV A
Source df MS F p Comparison
E.Kti H-Q IQ !-3 mQnlb~l Fronds (time) 35 0.279 0.53 ns Ho: J.l1=J.l2 reject; different<control Border 2 6.281 17.334 • Ho: J.l1=113 accept; different=clearcd Residual 70 0.362 Ho: 112=113 reject; control>cleared
113 =J.l1 ;t).l2
EXU {t-Q tQ t-3monthsl Cover (time) 35 95.12 0.291 ** Ho: J.l1=J,l2 reject; different<<control Border 2 8005.07 74.649 * Ho: J.l1=113 reject; different>clearcd Residual 70 107.24 Ho: J.l2=113 reject; control>>eleared
(EXP. 2) {t-Q to 1-2 monUJll Cover (time) 53 114.20 0.522 ** Ho: J.l1=J.l2 reject; different<<control Border 2 4831.23 36.72 * Ho: J.l1=113 reject; differcnt>clearcd Residual 106 131.57 Ho: J.l2=113 reject; control>>eleared
113 "111 "112
56
Table 7 Relative abundance (per m2) of benthic invertebmtes living in rocl.:y
intertidal habitats with and without seasonal sand cover. Quadmts (0.10m2) were sampled at random locations along 50m horizontal tmnsects at 3 elevations mnging from -0.1 to 2.5m. Areas were san1pled in summer and winter of 1990. Numbers indicate mean and ±1 standard deviation (n=60). *Balanus glandula are recorded as percent cover and are not included in the category All Species.
57
l1l 00
Waddell Bluffs
Rocky benches Y.ith no sand burial
All elevations
Rocky benches with sand burial
11.88 2.28 1.72 0.0 (5.20) (138) (1.20)
Summer
1.32 0.68 22.12 0.40 26.12 5.05 (1.00) (0.80) (932) (0.68) (9.60) (7.90)
All elevations nd nd nd nd nd nd 2.80 nd nd
Scott Creek
Rod.')' benches with no sand burial
All elevations
Rock-y benches with sand burial
All elevations
21.76 132 2.80 1.60 1.28 6.68 (732) (0.40) (1.20) (0.68) (1.08) (0.28)
nd nd nd nd nd nd
(2.00)
8.68 0.52 27.04 5.58 (4.12) (6.68) (10.80) (7.16)
2.53 nd nd (2.12)
16,60 132 1.00 (0.68) (0.12) (0.12)
0 0 0
Winter
o.o 0.80 0.52 38.52 032 24.12 {0.68) (0.12) (332) (0.12) (2.12)
7.39 (13.77)
0 0 0 11.60 0 (1.72)
16.91 1.45 (1.24) (·UO)
19.08 1.88 2.52 1.60 132 1.08 532 0.52 19.72 4.16 (1.56) (1.20) (0.20) (0.28} (0.40) (1.08) (0.52) (0.80) (3.72) (6.20)
0 0 0 0 0 0 6.00 0 (1.48)
27.96 0.75 (0.88) (2.11)
Table 8 Seasonal differences in invertebrate density were analyzed with two-tailed
independent t-tests between selected seasons, habitats and sites (n=60). *p<0.05, **p<O.Ol, ns=non significant (p>0.05). Summer/sand comparisons were not made due to limited data
59
INVERTEBRATE DENSITillS
Comparison t p
Waddell Bluffs
sand vs non-sand winter 16.83 **
winter vs summer non-sand 2.73 *
Scott Creek sand vs non-sand
winter 0.71 ns winter vs summer
non-sand 5.42 *
60
Table 9 Grain size analysis of sediment from algal habitats and Waddell Creek
beach. Values indicate percentages from total size distribution or sorting value. Balded values indicate dominant gmin sizes. Sediment class size divisions are: coarse gmin= 2.0-1.0 mm, medium gmin= 0.354-0.177 mm, fine gmin= 0.125-0.088 mm, and silt= <0.088 mm. N=3. Silty sediment was <1 o/o for both seasons at all areas.
61
Summer 1221 Winter 1222 (sieve diameter in mm) (sieve diameter in mm)
¢ 1.0 0.354 0.250 0.177 0.125 1.0 0.354 0.250 0.177 0.125 0.088
Polysiplzonia pacifica 0.07 0.02 0.781 0.17 <I 0.01 0.71 0.2 0.04 An tho pleura elegantissima 0.03 0.91 0.02 0.02 <I 0.04 0.70 0.06 0.16 <I
0\ Plzyl/ospadix sp. 0.05 0.72 0.18 <I <I 0.51 0.27 0.2 0.'01 t.J
Ulva sp. 0.04 0.47 0.31 0.08 0.05 0.06 0.54 0.09 0.25 0.04
Waddell beach 0.08 0.79 0.03 0.01 0.12 0.68 0.09 0.06 <I Waddell seasonal beach <I 0.66 0.26 0.03 0.03 0.09 0.73 0.08 0.08 <I
Figure 1 Map of pcm1ancnt sampling stations at Waddell Bluffs and Scott Creek in
central California. Numbers indicate station reference markers on rod.)' shale bench outlines.
63
l ~
~ : 0 0
64
Figure 2 Winter (top) and summer (bottom) cover of beach sand over the rocky shale
benches under Waddell Bluffs. Arrow indicates natural boulder reference mark. Distance between the 2 boulders in the forefront is 36 meters.
65
66
Figure 3 Field design for the reciprocal tmnsplant experiment Factors include sand
depth (low, high), and border effect (none, 10 em). Three treatment levels (reciprocal transplant, reciprocal tmnsplant with a 10 em clearing, and a control tmnslocation) were used to test the response of transplanted algae to different sand habitats (n=5). Qualitative "natural" controls of unmanipulated plants within each recipient patch were also examined (not shown). Recipient patches (n=6) in high and low sand habitats dominated by Mastocarpus papillalils and Polysiplwnia pacifica, respectively, were chosen mndomly. Percent cover and number of thalli were measured over a 6 month interval for P. pacifica and M. papilla/us, respectively.
67
DIAGRAM OF RECIPROCAL TRANSPL4.NT EXPERIMENT
Recipient Patches
00 80
M3
Polysiphonia patch
Mastocarpus patch
~ ~--E--1-- translocation control
n-5 in each recipient patcH
~ Mastocarpus papilla/us
~ Mastocarpus papilla/us ~ with !Ocm border
Polysiphonia pacifica
Polysiphonia pacifica with 10 em border
low sand habitat= Po/ysiphonia
high sand habitat= A1astocarpus
Figure 4 Seasonal change in sand depth in rocky intertidal habitats at Waddell Bluffs
and Scott Creek sites. Data were collected monthly for 14 months from May 1988 through August 1989. Each point represents the mean (±1 standard error) of measurements from random locations (n=lO).
69
120 U/va sp. habitat
120 Red and Brown Algal habitat
--o- Waddeii-Sta. - o<~-- Waddcli-Sb, 4
_ -co _ Waddeii-Sta. 6 --o--- Waddeii-Sta. 5
100 -- Scott-Sta, 3 100
E' 80 E' 80 ~ .s .s _c
_c I o_ o_ 60 I ru 60 u ru u
u u 2 c ~ nl c I w nl 40 w 40 \ I 0 I I 1 I \
20 20 \ / •
/ .S~i.
0 0 J A s 0 N D F M A M J J A J A s 0 N D J F M A M J J A
1988 1989 1988 1989 ...-J 0
Po/ysiphonia pacifica habitat 20 Anthopleura elegantissima habitat
20
----o-- Waddeii-Sta. 3 -o-- Waddeii-Sta. 1
- i;>· - Waddeii-Sta, 9 ---- Scott-Sta. 4
_.._ Scott-Sta. 2 15 15
E E .s .s _c _c o_ o_
10 ru 10 ru u '0 u '0 c c nl nl w w
5 5
JASONDJFMAM J A 1988 1989 1988 1989
Figure 5 Tree diagram resulting from average linkage clustering using Ward
Minimum Variance Method on percent cover data. Euclidean distance was used to measure similarity, demonstrated by clustering of independent stations (and replicates) into 4 distinct groupings characterized by taxonomic relationship. Labels indicate site (Waddell Bluffs, w, and Scott Creek, s), station number, and replicate number (1-5).
71
r ~ ~
1-1-1-. r
y lr ~
1 1-1-1-1-
L.
~ r
II-1'-lr-II-
' L. t.c r
'--~ ~ 1'-'--~
~ l[
L.
3:JNV .LS 10 NV30 11;)03 0
72
Figure 6 Percent cover of Ulva spp. and sand depth for intertidal sites dominated by
Ulva spp. Data were collected monthly from July 1988 through August 1989. Sand depths and percent algal cover are the mean (±1 standard deviation) of 10 and 5 measurements from random locations, respectively. nd=no data for percentage algal cover. Note scale change from a, c to b. Areas indicating an unknown percent cover due to sand are designated with [?] followed by a dashed line.
73
Waddell Bluffs-st. 2 Waddell Bluffs-st. 6 Scott Creek-st. 3 80 100 100 100 80 100
•
1'1 sand---
~ U/va-80 80
/I
80 80 60 60
~ ~ I . "' I I > E" I II
~ 0
60 I I I l 0
I I . 60 u ~ I 60
" .c I I I I l "' a. 40 I I I 40 I I I l " .._J <U I I I \ I I l c "0 iH .p.
"0 I 40 40
\~ ~ j \ 40 I 40 <U c:
' ? p I I I [!
"' I j \ <U "' I I I 1 0. 20 I
I 20 } I 20 20 \ 1 l I 0
d I 20 .l I I ? r ~..,\; ,Jl..} • 1-o "'0 "'0 ~· ' '"" f"'O'C-.::J "O"':::!'C"O "'"""""" ' ' ~"8 c c c 1::: ~ = 0 = 1::: = = 1::: = ......... c c c ' 0 0 0 0 0 J A 8 0 N D J M J J A J A 8 0 N D J F M A M J J A J A S D J F M A M J J A
1988 1989 1988 1989 1988 1989
Figure 7 Percent cover (n=5) of brown and red macroalgae and sand depth (n=lO)
for intertidal sites dominated by this mixed assemblage. Only species which held an average of>5% cover at some sampling date are included. nd=no data for percentage algal cover.
75
Waddell Blufls-sl. 4 Waddell Bluffs-sf. 5 120 100 120 100
sand ---
ri~ 100 algae-- 100 80 80
I I ft )l I I
80 "- 80 I I I ~
E I '£' I I If m
I > ~ I I 60 I I 60 0
I I "
.r:: I I I I ro -.J 0. 60 I I 60 I I I 0>
0\ m d I ro "0 I p I "0 I
I q ~ 40 I I <: c: I I
T 40 m
"' II I 9 fe "' 40 ~ I I I I 40 I m
J I I a.
\h I \
I I I I \ I I
20 fl I b' 20
? ~ I 20 I 20
I I I I ., I
I I I ~ ~ ~ ~ 0.. ~ ~ ~ 1l 1l 1l ~ ~ ~ ~ 1l ~
" • • . • " " . . • 0 0 0 • 0 J A s 0 N D J F M A M J J A J A s 0 N D J F M A M J J A
1988 1989 1988 1989
Figure 8 Percent cover (n=S) of Polysiplwnia pacifica and sand depth (n=lO) for
intertidal sites dominated by Polysiphonia.
77
Waddell Bluffs-st. 3 Waddell Bluffs-st. 9 Scott Creek-st. 2 60 100 60 100 60 100
50 50 50 80 80 80
E' 40 "' •10 :;; > -2- 6D 0
" _c m li 30 30 30 0> "' m "' --l
"' 40 40 40 c 00 c: 20 "' Ill 20 20 sand ~ "' Polysiphonfa "' 20 CL
20 1 20 10 "\
10 10
'~~...-a" .f A. I I \ )'-.~.._ o-o-a"' \ -- .. I .._t'l""'.a-11--.n....
0 0 0 0 ~-~ • 0 0 J A A S ON D J F M AM J J A J A S ON D J F M A M J J A
1988 1989 1988 1989 1988 1989
Figure 9 Percent cover (n=S) of Allllwpleura elegantissima and sand depth (n=lO)
for intertidal sites dominated by the sea anemone.
79
Waddell Bluffs-st. 1 Scotts Creek-st. 4
10 100 10 100
sand ---Anthop/eura --
8 80 8 ;:; 80 I
I I I ~
ID
I I I >
E" 0
I I 6
I u
-'!. 6 I I 60 I 60 ID
.c I I I c: 0
00 0. I I E 0 "' I I "' "0
f~\ I ·~ "0 4 I I 40 4 I 40
c:
f\ kt 1~\ I~ I ;:
::l I I ID
I J "' I
\ IL2 "' t 'tl 1~1 I I
o_
2 I I 20 2 20
II r \ .h- I f !'--£'
I I /
'd I 0 0 0 0
J A S 0 N D J F M A M J J A J A s 0 N D J F M A M J J A 1988 1989 1988 1989
