REPORT

Cryptofauna of the epilithic algal matrix on an inshore coral reef,Great Barrier Reef

M. J. Kramer • D. R. Bellwood • O. Bellwood

Received: 2 February 2012 / Accepted: 5 June 2012 / Published online: 22 June 2012

� Springer-Verlag 2012

Abstract Composed of a collection of algae, detritus,

sediment and invertebrates, the epilithic algal matrix

(EAM) is an abundant and ubiquitous feature of coral reefs.

Despite its prevalence, there is a paucity of information

regarding its associated invertebrate fauna. The cryptofa-

unal invertebrate community of the EAM was quantita-

tively investigated in Pioneer Bay on Orpheus Island, Great

Barrier Reef. Using a vacuum collection method, a diver-

sity of organisms representing 10 different phyla were

identified. Crustacea dominated the samples, with harpac-

ticoid copepods being particularly abundant (2025 ± 132

100 cm-2; mean density ± SE). The volume of coarse

particulate matter in the EAM was strongly correlated with

the abundance of harpacticoid copepods. The estimated

biomass of harpacticoid copepods (0.48 ± 0.05 g m-2;

wet weight) suggests that this group is likely to be

important for reef trophodynamics and nutrient cycling.

Keywords Crustacea � Harpacticoid copepods �Trophodynamics � Turf algae � Benthic community

Introduction

Coral reefs contain a complex range of microhabitats (Preston

and Doherty 1994; Purcell and Bellwood 2001). The epilithic

algal matrix (EAM) is one such microhabitat, covering dead

coral surfaces, that accounts for 30–80 % of the total surface

area on coral reefs (Klumpp and McKinnon 1992; Goatley and

Bellwood 2011). Prior to 1997, the EAM was referred to as the

‘epilithic algal community’ due to an assumption that the most

important component, in terms of abundance and trophody-

namics, was filamentous turfing algae (Scott and Russ 1987;

Klumpp and McKinnon 1992; Wilson and Bellwood 1997).

However, over the years, our understanding of the

importance of other EAM components has slowly grown

(Wilson 2000; Purcell and Bellwood 2001; Wilson et al.

2003). Major constituents of the EAM are now known to be

individually abundant and collectively diverse, creating a

complex matrix of short turfing algae which contains detri-

tus, microbes, microalgae and an invertebrate cryptofauna

(organisms between 0.06 and 4 mm in size) (Zeller 1988;

Purcell and Bellwood 2001; Wilson et al. 2003). Of these

constituents, the importance of algal turf and detritus is rel-

atively well documented (Choat et al. 2002; Depczynski and

Bellwood 2003; Wilson et al. 2003; Wilson 2004; Fox and

Bellwood 2007; Bonaldo and Bellwood 2011). In contrast,

much less is known regarding the EAM invertebrate cryp-

tofauna (but see Zeller 1988; Logan et al. 2008).

Initial investigations of coral reef cryptofauna have identi-

fied many different taxa, the majority of which are crustaceans

(Alldredge and King 1977; Klumpp et al. 1988; Logan et al.

2008; Enochs and Manzello 2012). Studies suggest that the

most abundant crustaceans on coral reefs are decapods on live

coral (Stella et al. 2010), and harpacticoid copepods and Per-

acarida on dead coral (Peyrot-Clausade 1980; Klumpp et al.

1988; Preston and Doherty 1994; Logan et al. 2008). However,

Communicated by Biology Editor Dr. Mark Vermeij

Electronic supplementary material The online version of thisarticle (doi:10.1007/s00338-012-0924-x) contains supplementarymaterial, which is available to authorized users.

M. J. Kramer (&) � D. R. Bellwood � O. Bellwood

School of Marine and Tropical Biology, James Cook University,

Townsville, QLD 4811, Australia

e-mail: michael.kramer@my.jcu.edu.au

M. J. Kramer � D. R. Bellwood

Australian Research Council Centre of Excellence for Coral

Reef Studies, James Cook University, Townsville, QLD 4811,

Australia

123

Coral Reefs (2012) 31:1007–1015

DOI 10.1007/s00338-012-0924-x

the relative abundance of Crustacea in relation to other resident

taxa in the EAM is largely unknown (but see Logan et al. 2008).

Although the EAM appears to be a relatively uniform,

almost two-dimensional habitat (Fig. 1), previous studies have

documented considerable variation in EAM composition,

especially in terms of particulate loads, amongst reef zones (e.g.

Purcell and Bellwood 2001; Wilson et al. 2003). The effect of

particulate matter on some cryptofaunal groups is well docu-

mented (e.g. Hicks 1980; Logan et al. 2008; Takada et al. 2008).

Nevertheless, the relationship between particulate matter in the

EAM and its crustacean cryptofauna remains unclear.

The ubiquitous presence of the EAM as a coral reef habitat

suggests that its invertebrate cryptofaunal community is likely

to provide a significant food resource for higher trophic levels

(Peyrot-Clausade 1980; Klumpp et al. 1988; Carleton and

McKinnon 2007; Enochs and Manzello 2012). Quantitative

investigation of the EAM cryptofaunal community will

therefore provide a greater understanding of the trophic

importance of these small organisms in fine-scale processes,

such as microherbivory, on coral reefs. It will also establish

their potential contribution to higher trophic levels. This study

aims to investigate the invertebrate cryptofauna of the EAM

on an inshore coral reef system, with particular emphasis on

the crustacean component. The specific objectives are as

follows: (1) to quantify the abundance and biomass of major

taxa present and (2) to evaluate the relationship between the

volume of particulate matter within the EAM and the abun-

dance of harpacticoid copepods in the cryptofauna. The

findings of this study will provide a quantitative indication of

the relative importance of major taxa in the EAM and their

potential implications for coral reef trophodynamics.

Methods

Location

This study was conducted between February and March 2011

in Pioneer Bay, Orpheus Island (18�350S, 146�200E), on the

inner Great Barrier Reef (GBR), Australia (Fig. 2). Orpheus

Island was chosen as a representative inshore reef on the

GBR. The area has moderate sediment loadings and easily

defined EAM surfaces dominated by short turfing algae.

Pioneer Bay has an extensive fringing reef, comprising of a

reef flat that extends approximately 150 m from the shore-

line to the reef crest, where the reef gradually slopes down to

sand at approximately 15 m depth (Fox and Bellwood 2007).

Four sites were selected across the bay. At each site, 5

samples were taken from each of three zones: outer reef flat,

reef crest and reef base. The outer reef flat was defined as the

area approximately 15 m shorewards of the reef crest where

coral cover decreased but turfing algae were predominant over

macroalgae. The greatest coral cover and structural complexity

occurred at the reef crest, where the non-coral substrate was

dominated by algal turf. The reef base at 6–8 m was charac-

terised by high levels of sedimentation covering a dead coral

substrate (for further details see Fox and Bellwood 2007).

Sampling equipment construction

A vacuum sampler (modified after Purcell 1996) was used to

take samples directly from the EAM. The vacuum sampler is

a submersible piece of equipment that consists of three

components: a filter to retain particles greater than 60-lm, a

pump to create current and a collection bag to retain fine

particulate matter that passes through the filter. These com-

ponents were connected in sequence by 15-mm aquarium

tubing. The filter mechanism was constructed from a 250-mL

acrylic sample vial with a 14-mm hole drilled into both the

screw-top lid and the base. Into these holes the flexible

aquarium tubing was inserted. The tubing extended 5-mm

into the filter canister at the base and 30-mm at the lid. A

60-lm plankton mesh bag was secured onto the tubing

inserted through the lid using a rubber band. This mesh bag

retains sediment, large detrital matter and small invertebrates.

A 305 9 455 mm plastic bag was secured to the outflow tube

using a rubber band to collect fine sediments and detritus. The

pump consisted of an electric bilge pump (Rule iL200, 12 V

Slimline submersible pump) that was connected to a 12 V

battery mounted within a waterproof PVC housing.

Sample collection

The sampling areas consisted of flat, horizontal surfaces

covered in an epilithic algal matrix. EAM collection sites were

selected based on the presence of visible turfing algae con-

taining sediment and detritus but no living coral. Samples

were collected on SCUBA during high tide. A PVC ring

(51-mm internal diameter) was haphazardly placed onto the

EAM surface to standardise and constrain the sampling area

(20.43 cm2). Once the plankton mesh bag was secured inside

the filter canister and the plastic bag secured to the outlet tube

Fig. 1 The epilithic algal matrix, containing an abundance of turfing

algae, detritus and a concealed cryptofauna. Scale is in millimetres

1008 Coral Reefs (2012) 31:1007–1015

123

of the vacuum sampler, the PVC ring was pinned against the

substrate. Prior to placing the intake of the vacuum into the

sampling area, care was taken to cover the entrance of the tube

to prevent holoplankton from entering the sample. The intake

tube was then pressed firmly against the substratum within the

sampling area and the flow switched on. All loose items were

drawn into the filter canister. Suction was maintained until all

visible sediment and detritus was removed from the sampling

area. Immediately after the vacuum was turned off, the

plankton mesh bag was removed from the tube and tightly

sealed with a rubber band in a manner that prevented any loss

of contents. Upon returning to shore, the filter bags were

placed into labelled sample vials and preserved in 4 %

phosphate-buffered formaldehyde. The particulate samples

were allowed to stand for approximately 12 h, after which the

upper layer of water was decanted off, following Purcell

(1996). The decanting process was repeated until approxi-

mately 30-mL of water and sediment remained. This solution

was pipetted into labelled 35-mL sample vials, and the fluid

was again left for the particulate material to settle. The

remaining fluid was replaced with 4 % phosphate-buffered

formaldehyde, and the particulate matter was resuspended to

ensure adequate mixing of the preservative.

Laboratory procedures

For analysis, all samples were stained with Young’s eosin–

erythrosin to aid in distinguishing organisms from the par-

ticulates. The samples were analysed using an Olympus

SZ40 binocular microscope under 4 9 magnification, and

all visible organisms were identified to the lowest taxonomic

level (usually order) and counted. In addition, in five ran-

domly selected samples, all identified organisms within

these samples were measured (to the nearest 25-lm) using an

Olympus ocular micrometer.

Particulate samples (detritus and sediments) were placed

into identical 35-mL sample vials and agitated to suspend all

particles to ensure homogenous settling. The samples were

then allowed to settle for 48 h before measuring the depth of

the settled particulate matter using digital vernier calipers.

The depth measurements were then converted into volume

using a regression formula. This was calculated by placing

known volumes of water into the aforementioned 35-mL

sample vials and measuring the depth of the water. This was

repeated five times to obtain a mean depth for each volume.

A linear regression was calculated to obtain a formula for

estimating particulate matter volume based on depth.

The wet-weight biomass of harpacticoid copepods was

calculated using a published length/dry weight regression

(Dumont et al. 1975) in conjunction with dry-weight/wet-

weight conversion ratios (Omori 1969). Care was taken to

ensure that the body morphology of the species used for

calibration was similar to those observed in the present study.

This provided the formula for the conversion of length to wet

weight of an individual harpacticoid copepod, where W is the

wet weight in microgram and L is the length in millimetre.

W ¼ 7:69 � 12:51� L4:40� �

This information was then used to calculate the

approximate biomass of harpacticoid copepods within a

defined area of the EAM.

250 km 20 km

1 km

Queensland

Pioneer Bay

Palm Islands

Na

b

c

Townsville

Orpheus Island

18° 35’ S

146° 20’ EFig. 2 Study site location.

a Queensland, Australia;

b Townsville and the Palm

Islands; c Orpheus Island and

Pioneer Bay. Dashed line

indicates the reef crest of the

fringing reef

Coral Reefs (2012) 31:1007–1015 1009

123

Statistical analysis

Abundant data were visually analysed using a multidimen-

sional scaling (MDS) ordination based on a Manhattan dis-

tance matrix on proportional data. In addition, the

community composition was compared using a permuta-

tional multivariate analysis of variance (PERMANOVA)

based on a Manhattan distance matrix on proportional data.

This distance measure was chosen as it is robust to double

zeros and is appropriate for abundance data. In the PER-

MANOVA design, site was designated as a random factor

and zone as a fixed factor. Similarly, the comparison of

harpacticoid copepod biomass across sites and zones was

analysed using an ANOVA, with site as a random factor and

zone as a fixed factor. Data analysed using the ANOVA were

square root transformed to meet assumptions of normality.

The relationship between the volume of particulate

matter and the abundance of harpacticoid copepods was

analysed using Pearson’s product–moment correlation on

square root-transformed coarse particulate volume and

harpacticoid abundant data, and log-transformed fine par-

ticulate volume data, to meet assumptions of normality.

Results

Cryptofauna in the epilithic algal matrix

From the EAM, 23 major taxonomic groups were identi-

fied. Taxa were derived from a total of 10 phyla, of which

the Arthropoda (Crustacea), Foraminifera, Nematoda,

Mollusca and Annelida were particularly abundant,

regardless of reef zone (Fig. 3a). These phyla were present

in all samples, whereas the organisms classed in ‘other’

were less common, often being absent from a sample.

These included Chaetognatha, non-crustacean Arthropoda,

Echinodermata, Chordata and Gastrotricha.

Crustaceans were particularly abundant in the EAM. A

taxonomic evaluation divided samples into 10 major

groups, the most abundant of which included the Harpac-

ticoida, Ostracoda, Cyclopoida and assorted crustacean

nauplii (Fig. 3b). Other less common taxa included Calan-

oida, Tanaidacea, Amphipoda, Cumacea, Isopoda and

Caridea. The most prominent group of crustaceans observed

in the EAM were harpacticoid copepods, regardless of site

(Fig. 3b), with a maximum density on the reef crest of

2397 ± 254 (mean ± SE) individuals 100 cm-2.

The PERMANOVA analysis found a significant differ-

ence in site (P \ 0.05) and zone (P \ 0.05), with a signifi-

cant interaction term (P \ 0.05). Thus, the differences in

zones are not consistent amongst sites. The data are grouped

into zones for ease of graphical representation, as the sig-

nificant zone and site effects are likely to be driven by a few

rare organisms that were found only on the reef flat (i.e.

Pycnogonida, Gastrotricha and Cephalaspidea). The full

site-level data are presented in the Electronic Supplemental

Material (ESM Fig. S1). The MDS suggests that although a

statistical significance exists, the biological significance may

not be marked as there is an extensive overlap in the com-

munity composition across the three reef zones (Fig. 4a).

A PERMANOVA of the Crustacea across all zones

revealed significant differences in site (P \ 0.05) and zone

(P \ 0.05), but there was no significant interaction between

the two (P [ 0.05). The MDS of Crustacea assemblages

across all zones again displayed a high degree of overlap,

indicating that the statistical significance (possibly driven

by slight differences in abundances on the reef flat) may

again not indicate marked biological significance (Fig. 4b).

Biomass of harpacticoid copepods

The average length of harpacticoid copepods was

0.43 ± 0.0035 lm (mean ± SE, n = 1689). The weight of

an individual harpacticoid copepod, assuming a mean length

of 0.43 ± 0.0035 lm, was found to be 2.37 ± 1.43 9

10-09 lg (wet weight). Because the standard error was small,

it had a negligible influence on the final weight and was not

considered in further calculations. Instead, to calculate error

in harpacticoid copepod weights by reef zone, the error

0

500

1000

1500

2000

2500

3000

3500

4000

Arthropoda (Crustacea)

Foraminifera Nematoda Mollusca Annelidia other

Mea

n a

bun

dan

ce 1

00 c

m-2

± S

E

Phylum (Subphylum)

Base

Crest

Flat

a

b

0

500

1000

1500

2000

2500

3000

Harpacticoida Nauplii Ostracoda Cyclopoida other

Taxonomic Group

Base

Crest

Flat

Fig. 3 Taxonomic groups in vacuumed EAM samples across a reef

profile: a Phyla (Subphyla) and b Crustacea (mean ± SE)

1010 Coral Reefs (2012) 31:1007–1015

123

associated with abundance was used. The wet-weight bio-

mass estimates of harpacticoid copepods amongst zones

ranged between 0.39 ± 0.03, 0.57 ± 0.06 and 0.48 ±

0.06 g m-2 for the base, crest and flat zones, respectively

(ESM, Fig. S2). There was no statistical difference in the

biomass of harpacticoid copepods across sites (F3,6 = 0.75,

P [ 0.05), or zones (F2,6 = 1.13, P [ 0.05). There was,

however, a significant interaction effect (F6,48 = 5.72,

P \ 0.05), which was largely due to the base being signifi-

cantly difference to the crest (Tukey HSD, P \ 0.05) and the

flat (Tukey HSD, P \ 0.05), whereas there was no signifi-

cant difference between the crest and the flat (Tukey HSD,

P [ 0.05).

Particulate matter

The volume of particulate matter less than 60-lm was not

significantly correlated with the abundance of harpacticoid

copepods (Fig. 5a; r = 0.053, df = 58, P [ 0.05). In

contrast, the volume of particulate material greater than

60-lm had a strong positive relationship with the abun-

dances of harpacticoid copepods (Fig. 5b; r = 0.56,

df = 58, P \ 0.001).

Discussion

This study provides a quantitative investigation of the

cryptofauna of the EAM. Although nine phyla were

recorded, harpacticoid copepods were by far the most

abundant organism in the cryptofauna and are thus the

primary focus for further discussion. This study reports the

highest density of harpacticoid copepods on a reef sub-

stratum, to date. This is probably a result of both the

methods used and habitat sampled.

Dimension 1-3 -2 -1 0 1 2 3

Dim

ensi

on 2

-2

-1

0

1

2

BaseCrestFlat

HarpacticoidaNauplii

Cyclopoida

Ostracoda

Stress = 0.100

BaseCrestFlat

Dimension 1

-4 -2 0 2 4

Dim

ensi

on 2

-2

-1

0

1

2

Stress = 0.133

Harpacticoida

Foraminifera

Nematoda

CyclopoidaNauplii

a

b

Fig. 4 Multidimensional scaling analysis of a the total invertebrate

and b the Crustacea community assemblages of the EAM across three

reef zones. Dashed and solid lines indicate zone groupings

Volume of coarse particulate matter ( (mL) )

Num

ber

of h

arpa

ctic

oid

cope

pods

( √

(abu

ndan

ce)

)

5

10

15

20

25

30

35

0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8

Num

ber

of h

arpa

ctic

oid

cope

pods

( √

(abu

ndan

ce)

)

Volume of fine particulate matter ( ln (mL) )

5

10

15

20

25

30

35

-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2

a

b

√

Fig. 5 Scatterplots with line of best fit of the relationship between

harpacticoid copepod abundance and a fine particulate matter

(\ 60 lm) (r = 0.053, df = 58, P [ 0.05) and b coarse particulate

matter ([ 60 lm) (r = 0.56, df = 58, P \ 0.001)

Coral Reefs (2012) 31:1007–1015 1011

123

Abundance of harpacticoid copepods

Although previously published data on harpacticoid abun-

dances on coral reefs revealed a wide range of results

(Table 1), the densities of harpacticoid copepods reported

herein are almost double previous reports. The variability

in harpacticoid copepod density values may reflect habitat

variability, as the sites range from fringing inshore reefs

(e.g. Orpheus Island, present study) to mid-shelf reefs (e.g.

Davies Reef, Klumpp et al. 1988). However, it is most

likely a result of different sampling methods. In the present

study, the sampling equipment was able to remove a high

proportion of organisms and, in conjunction with a small

mesh size, was probably able to collect most cryptofauna

present in the EAM.

The particularly high abundance of harpacticoid

copepods in the EAM is consistent with other studies

where they appear to be numerically dominant across a

variety of benthic habitats (Hicks 1980; Coull and Wells

1983; Gheerardyn et al. 2008; Folkers and George 2011).

These studies suggest that the primary factor determining

the abundance of harpacticoid copepods is the hetero-

geneity of the substratum. Variation in habitat com-

plexity on a macroscale (10 cm–10 m) has been widely

recognised in the literature as an important factor in

determining the diversity and abundance of reef fish

assemblages (e.g. Friedlander and Parrish 1998; Syms

and Jones 2000; Wilson et al. 2006), and more recently,

macroinvertebrates (Vytopil and Willis 2001; Enochs

et al. 2011; Enochs 2012). Superficially, the EAM

appears to have very low macroscale complexity. How-

ever, the results of the present study suggest that the

EAM may exhibit structural complexity on a much

smaller scale (\ 5 mm), providing a habitat for a diverse

cryptofaunal invertebrate assemblage that remains rela-

tively uniform in composition across sites and habitats

(statistical variation notwithstanding).

To support the high abundance of harpacticoids, a cor-

respondingly abundant nutritional source must also occur

to support the population. In this regard, the EAM offers a

rich resource of microalgae (Klumpp and McKinnon 1989;

Wilson et al. 2003). In many ecosystems, the biomass of

benthic microalgae often exceeds that of the phytoplankton

in overlying waters, contributing a significant proportion to

ecosystem productivity (MacIntyre et al. 1996; Buffan-

Dubau and Carman 2000). Indeed, benthic primary pro-

duction is approximately 90 % greater than the produc-

tivity of lagoon waters on the GBR (Roman et al. 1990).

This primary productivity is likely to be the key resource

that supports the population of harpacticoid copepods,

which feed primarily on microalgal films on the substrate

(Carman and Thistle 1985; Klumpp et al. 1988; Buffan-

Dubau et al. 1996).

The numerical dominance of harpacticoids in the EAM

examined in the present study suggests that they are likely

to be major consumers of benthic microalgae. Other studies

have suggested that organisms such as Ostracoda are also

important consumers (Blanchard 1991; Buffan-Dubau and

Carman 2000). However, Montagna et al. (1995) manipu-

lated the biomass of microalgae (measured in concentration

of chlorophyll a) in an intertidal system and observed the

effects on grazing ostracods and harpacticoid copepods. A

390 % increase in chlorophyll a concentration was found

to correspond with a 270 % increase in harpacticoid bio-

mass, but no observable change in ostracod biomass

(Montagna et al. 1995). As harpacticoid copepods are the

most abundant group of organisms in the EAM, their rel-

ative contribution to the consumption of microalgae in

relation to other taxa is likely to be significant, but this

requires confirmation by experimental investigation.

Biomass of harpacticoid copepods

Despite their high abundance, harpacticoid copepods are

rarely acknowledged members of a ‘typical’ coral reef

community. Although the estimated biomass of harpacti-

coid copepods from the present study appears to be rela-

tively small in terms of a standing-stock weight per unit

area, these microscopic organisms are likely to be impor-

tant components of the fauna of both the EAM and coral

reefs as a whole. This importance can be seen when

comparing the mean dry-weight biomass of harpacticoid

copepods in the present study (62.49 ± 6.59 mg m-2) to

pelagic zooplankton dry-weight values on the GBR, which

range from 0.88 to 4.30 mg m-3, with a mean of approx-

imately 1.37 mg m-3 (Roman et al. 1990). Even when

considering the total amount of pelagic zooplankton in, for

Table 1 Published maximum densities of harpacticoid copepods on

coral reefs, using a range of collection methods and mesh sizes

Maximum

Harpacticoida

density ind.

100 cm-2 (± SE)

Location

(All

GBR)

Collection

method

Sieve

mesh

size

(lm)

Source

97.6 (8.5) Orpheus

Island

Settlement

plates

200 Zeller

(1988)

154.2 (168.2) Davies

Reef

Enclosing

dead coral

in sealed

bags

200 Klumpp

et al.

(1988)

1182.4 (523.3) Heron

Island

Venturi

suction

sampler

100 Logan

et al.

(2008)

2397.3 (254.8) Orpheus

Island

Electronic

suction

sampler

60 Present

study

1012 Coral Reefs (2012) 31:1007–1015

123

example, an arbitrary 5-m water column, the mean biomass

(6.85 mg m-2) is still approximately an order of magnitude

lower than that recorded from the benthos, where the

Crustacea are concentrated into a 4–10-mm-thick bed of

EAM.

The generational time, and thus approximate biomass

turnover of harpacticoid copepods, ranges between 8 and

29 days, with most species falling within 12–17 days

(Harris 1977; Cutts 2003; Ajiboye et al. 2011). However,

this information is based largely on temperate species; the

copepods in the present study will probably have much

faster generational times in the warmer tropical waters.

This is very likely to produce an abundant and valuable

trophic resource for small, benthic predatory vertebrates

and invertebrates on coral reefs, as harpacticoid copepods

have been shown to be a valuable resource for fish across a

wide variety of habitats (Bellwood 1988; Tipton and Bell

1988; Coull 1990; Edgar and Shaw 1995). It is common for

small animals to produce, on average, an equal or greater

amount of biomass over time than their larger counterparts,

despite their considerably lower standing biomass. This is

due to the higher relative magnitude of abundance, popu-

lation turnover rates and individual growth rates per unit

weight of small organisms (Damuth 1981; Calder 1984).

Therefore, the abundance of small crustacean grazers (i.e.

harpacticoid copepods) and the subsequent consumption of

primary producers present a potentially important compo-

nent in the trophic transfer of resources in shallow water

systems (Kitting et al. 1984; Fredette et al. 1990; Edgar and

Shaw 1995; Taylor 1998).

Effects of particulate matter

The presence of large detrital particles and carbonate

sediments (particulate materials) on coral reefs has a range

of positive and negative effects on the benthic biota. High

sediment levels adversely affect both the growth and health

of corals (Rogers 1990; Wittenberg and Hunte 1992) and

the feeding of herbivorous fishes (Bellwood and Fulton

2008). Conversely, particulate materials are well docu-

mented to have a positive effect on cryptofaunal densities

(Hicks 1980; Gibbons 1988; Danovaro and Fraschetti

2002; Gheerardyn et al. 2008; Logan et al. 2008, Takada

et al. 2008). This positive interaction is suggested to be due

to increased substrate heterogeneity and thus habitat

availability for benthic organisms such as nematodes and

cumaceans (Hicks 1980; Danovaro and Fraschetti 2002;

Logan et al. 2008).

Particulate matter and sediments are readily trapped

amongst the short turfing algae of the EAM (Purcell and

Bellwood 2001), thereby increasing the spatial heteroge-

neity of this microhabitat. In the present study, the inter-

action between particulate matter and the most abundant

organism in the EAM (harpacticoid copepods) was ana-

lysed. Interestingly, no increase in the abundance of

harpacticoid copepods was seen with increase in the vol-

ume of fine particulate matter (\60 lm). This was sur-

prising, as fine particulate matter is likely to be very rich in

amorphous organic matter, an important food source for

many organisms (Wilson et al. 2003). Instead, an increase

in abundance of harpacticoid copepods was seen with an

increase in the volume of coarse particulate matter. This

suggests that the habitat complexity provided by the coarse

particulate matter is a more influential environmental dri-

ver affecting abundance of harpacticoid copepods. In

addition, the increased surface area provided by the coarse

particulate matter may increase microalgal biomass capa-

ble of supporting a high biomass of micro-grazing crusta-

ceans such as harpacticoid copepods. The process of

microbial stripping, by which organisms ingest particulate

matter but only digest the microbial organisms (Lopez and

Levinton 1987), may be an important activity that is

facilitated by the continual production and consumption of

the EAM microflora, whilst still maintaining the abundance

of particulate matter. The interacting effects of habitat

complexity and nutritional availability may explain the

increase in harpacticoids with the increase in the volume of

coarse particulate matter observed in the present study.

Trophic potential

The high abundance, rapid turnover and fast growth rates

of small organisms such as cryptobenthic fishes underpin

their critical role in ecosystem processes in reef systems

(Depczynski et al. 2007). In this regard, small, highly

productive crustaceans such as harpacticoid copepods may

be important for the same reasons. However, the contri-

bution of EAM cryptofauna as a trophic component of the

diet of other coral reef groups, particularly functionally

important reef fishes, remains to be determined. The

present study provides a quantitative account of the

invertebrate cryptofaunal community of the EAM on coral

reefs. It revealed a surprising range of taxa in the EAM and

a high abundance of harpacticoid copepods. Additionally,

the importance of particulate matter in the EAM is espe-

cially relevant to the cryptofauna, presumably providing a

valuable habitat and facilitating the growth and availability

of microalgae. Current knowledge of the diversity and use

of resources in the EAM is weighted towards algal and

detrital components (Wilson et al. 2003). The information

presented herein highlights the potential importance of

Crustacea and provides a foundation from which the

potential trophic importance of EAM Crustacea to other

members of the wider coral reef community can be

investigated.

Coral Reefs (2012) 31:1007–1015 1013

123

Acknowledgments We wish to thank S Leahy, C Lefevre, J Welsh

and staff of Orpheus Island Research Station for their support in the

field; J Kidgell, J Leonhardt, J Levy, T Sih, K Stegemann and J Welsh

for their valuable assistance in processing samples; J Tanner for

comments and criticisms on final drafts of the manuscript; and five

anonymous reviewers for their helpful suggestions. This work was

supported by the Australian Research Council (D.R.B.).

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