intertidal oysters in northern new england

Eagle Hill Institute

Intertidal Oysters in Northern New EnglandAuthor(s): Mark Capone, Ray Grizzle, Arthur C. Mathieson and Jay OdellSource: Northeastern Naturalist, Vol. 15, No. 2 (2008), pp. 209-214Published by: Eagle Hill InstituteStable URL: http://www.jstor.org/stable/25177100 .

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2008 NORTHEASTERN NATURALIST 15(2):209-214

Intertidal Oysters in Northern New England

Mark Capone1,2*, Ray Grizzle1'2, Arthur C. Mathieson1'3, and Jay Odell4

Abstract - Little is known about the distribution and ecology of intertidal oysters in northeastern North America. North of Chesapeake Bay, intertidal oysters have either

been previously reported as non-existent or only occurring as single oysters or sparse

clusters. In the present study, we report the occurrence of dense populations of inter

tidal oysters at several estuarine sites within New Hampshire and mid-coastal Maine,

with these growing under dense canopies of the long-lived Ascophyllum nodosum

(fucoid alga). The densities of these northern intertidal oysters rival subtidal popula tions in the same geography, and their sizes suggest a persistence of 5 or more years.

Introduction

Crassostrea virginica (Gmelin) (eastern oyster) inhabits coastal and

estuarine waters from the Gulf of Saint Lawrence to the Gulf of Mexico

(Carriker and Gaffney 1996), occurring subtidally, intertidally, or in both

habitats. Intertidal populations are common in the South Atlantic (Bahr and Lanier 1981, Burrell 1986), limited in the mid-Atlantic (DeAlteris

1988), and are often described as non-existent in the Northeast (Kennedy and Sanford 1999, Whitlach 1982), presumably because extreme winter

temperatures and ice-scour cause high mortalities of oyster sets. In one

of the few studies of intertidal oysters in New England (i.e., Great Bay,

NH), Hardwick-Witman and Mathieson (1983) found low densities (<1?5.6

individuals/m2) of detached populations, which suggested to them a poten tial subtidal origin and ephemeral nature. By contrast, recent observations in New Hampshire and Maine have shown that intertidal oyster populations are more prevalent than previously suggested. In order to better characterize

these intertidal populations, we sampled oyster assemblages from six New

England estuarine sites, including three from Great Bay, NH and three oth ers from the upper reaches of the Damariscotta River near Newcastle, ME

(Fig. 1). We hope that enhanced knowledge regarding these persistent inter

tidal oyster assemblages will encourage future conservation, restoration, and a better understanding of their ecology.

Methods

Our initial studies at Weeks Point, NH (43o03'32"N, 70?51'42"W) were

conducted during October 21, 2005 at which point we visually inspected a

Jackson Estuarine Laboratory, 85 Adams Point, Durham, NH, 03824. depart ment of Zoology, Spaulding Life Sciences, University of New Hampshire, Durham, NH 03824. 3Plant Biology Department, Spaulding Life Sciences, University of New Hampshire, Durham, NH 03824. 4The Nature Conservancy, Virginia Pro

gram, Richmond, VA 22901. "Corresponding author - [email protected].



210 Northeastern Naturalist Vol. 15, No. 2

300-m length of shoreline for the occurrence of intertidal oysters, as well as

for general ecological conditions. Ten haphazardly placed quadrats (0.1 m2) were sampled within the Ascophyllum nodosum (L.) Le Jolis (knobbed wrack) zone of the intertidal zone. The elevation of each quadrat was determined us

ing a line level and a surveying rod (Dawes 1998, Mathieson et al. 1998), with

vertical heights above or below mean low water (MLW) calculated based on

predicted tidal levels (Harbor Master Program, Version 3, Zihua Software,

Marlboro, CT). Non-destructive sampling methods were used to determine

density, frond length (to nearest cm), annual growth rates, age, and amount of

apical pruning for ten Ascophyllum plants within each quadrat. Annual (i.e.,

total) growth rates for A. nodosum during the past year were determined by

measuring the mean length of intact apical tips that had originated from the

last terminal bladder (cf. Baardseth 1970). Age was determined by counting the number of bladders per frond, with the formation of the initial bladder as

sumed to have taken 4 years and additional bladders added yearly thereafter

(Baardseth 1970, Mathieson and Guo 1992). Canopies of Ascophyllum were

lifted and all bivalves present within each quadrat were identified and count

ed, and their shell heights, beak to lip, were measured to the nearest millimeter

with Vernier calipers. The remaining five sites included two locations within Great Bay, NH

and three on the upper reaches of the Damariscotta River, in Newcastle, ME:

Figure 1. Map of New England and Gulf of Maine. Arrows show the locations of

Great Bay, NH and Damariscota River, ME study sites.



2008 M. Capone, R. Grizzle, A.C. Mathieson, and J. Odell 211

Nannie Island (43?4'8.98M, 70?51,45.68"W) and Woodman Point, Green

land, NH (4304'18.55MN, 70?51,37.00"W), plus Goose Rocks (44?00'51"N,

69?32'56"W), the shoreline just west of this location (44?00'46"N,

69?32'56"W), and Hog Island (44?00,46"N, 69?32,35"W) within Newcastle, ME. The presence of oysters at each of these sites was noted, plus their oc

currence relative to fucoid algal coverage. Canopies of the fucoid alga A.

nodosum were lifted, and the presence or absence of oysters noted, as well as any additional understory organisms present. In addition, at Goose Rocks

only, haphazard samples of intertidal oysters were measured for shell height with Vernier calipers.

Results

Weeks Point

Oysters were present on rock outcrops along the entire 300-m section

of shoreline inspected, with nearly all live populations occurring under

Ascophyllum canopies (Fig. 2B). Rare single oysters or small clusters grew on some cobbles at the base o? Ascophyllum communities or on adjacent

Figure 2. A) Hog Island, ME intertidal zone illustrating typical habitat where oysters were found; note extent of rockweed covering rocks. B) Weeks Point, NH intertidal

oysters beneath rockweed. C) Ascophyllum and Fucus covering oysters at Hog Is

land, ME. D) Close-up of Goose Rock intertidal oyster community; note barnacles,

mussels, and Ascophyllum.




mudflats. Oyster densities ranged from 10 to 150 individuals/m2, with a

mean density of 57 ? 40.8 individuals/m2 (standard deviation); they ex

tended from 0.0 to +1.2 m. The mean oyster shell height was 60.1 ? 8.3

mm, with a maximum height of 89.5 mm. The ribbed mussel, Geukensia

demissa (Dillwyn), was also common amongst oysters, occurring with a

mean density and shell height of 11 ? 11.0 individuals/m2 and 35.1 ? 11.7

mm, respectively. The mean age of Ascophyllum plants was 7.2 ? 1.2 years, with a maximum age of 13 years. Ascophyllum densities ranged from 60 to

180 individuals/m2, with a mean density of 96? 35.5 individuals/m2; their mean frond length was 55.4 ? 16.6 cm. As determined by simple linear re

gression, oyster shell height was inversely related to tidal height (r2= 0.62,

p =

0.007). No significant relationships were found between oyster met

rics and plant metrics. Oyster size was not related to Ascophyllum length

(r2= 0.035, p =

0.29) nor density (r2 =

0.0011, p =

0.93), while oyster

density was also not related to Ascophyllum length (r2 =

0.17, p =

0.24) or

density (r2 =

0.029, p =

0.63).

Other New Hampshire/Maine sites

Similar intertidal oyster populations were found under Ascophyllum can

opies at the other five sites, with their densities being consistent with those

at Weeks Point. At Nannie Island and Woodman Point (i.e., New Hampshire)

oysters were rarely found on bare substrata, while newly settled oyster spat

(<30 mm shell height) were present in some areas. Ribbed mussels were

present at all three New Hampshire sites.

Mytilus edulis (Linnaeus) (blue mussels), Semibalanus balanoides (Lin

naeus) (acorn barnacles), and Littorina littorea (Linnaeus) (periwinkles) were present with oysters at all Maine sites. Attached oysters were present at 0.0 MLW on exposed bare substrata on the shoreline west of Goose Rock,

while above this elevation, they were restricted to subcanopy fucoid habi

tats. The mean shell height for oysters at the Goose Rock site was 63 ? 21.5

mm, with a maximum shell height of 109.5 mm.

Discussion

We are unaware of any previous reports of relatively high densities of

persistent intertidal oysters in the northeastern North America. This absence

suggests that historically they either did not persist or that their abundances

were so low that they did not warrant attention or detection. Anecdotal sto

ries from local New Hampshire oystermen support the first hypothesis, as

they are unable to recall the occurrence of intertidal oysters prior to the past ten years. Commercial oystermen in Maine also believe that the intertidal

expansion of oysters reported here is a recent phenomenon. It is possible,

given the cryptic nature of algal-covered intertidal oysters that they may have escaped detection; however, the alternative hypothesis (i.e., recent

expansion) deserves further attention.



2008 M. Capone, R. Grizzle, A.C. Mathieson, and J. Odell 213

High densities of intertidal oysters, up to 150 individuals/m2, were

found in New Hampshire and Maine under canopies of long-lived Asco

phyllum nodosum and attached to rocky substrata. Intertidal oysters provide a complex structure for the attachment of additional epifauna, such as ribbed mussels and barnacles. At low tide, the extensive rockweed cover

in these geographies can completely cover oysters (Fig. 2), protecting them

from environmental extremes (Bertness et al. 1999). As noted above, oysters were extremely rare on bare rocky substrata at

all study sites. Bare rock outcrops of equal size and tidal height compared to

those covered by Ascophyllum typically had no attached oysters. Small oys ters (<30 mm) were present on bare substrata at Nannie Island and Woodman

Point, showing that larval supply did not necessarily limit intertidal oyster distribution. While they can reach 109.5 mm under extensive Ascophyllum coverage, the absence of large oysters on bare substrata suggests that post

settlement mortality limits their distribution.

The intertidal zone where Ascophyllum and Fucus vesiculosus L. (blad der wrack) occur within the Great Bay estuarine system is estimated to be

130,000 m2or 32.12 acres (Josselyn 1978). If the entirety of this zone were

inhabited by oysters at densities found in this study, there could be 7.4 x

106 ? 5.3 x 106 intertidal oysters or roughly 36% of Great Bay's known sub tidal oyster population (Trowbridge 2005) presently unaccounted for in the

management of this resource.

In summary, northern intertidal oysters require further examination. Have these populations recently expanded due to climate-related shift in habitat utilization caused by global warming (Sagarin et al. 1999) or have

they simply been missed during previous studies? Further, why do oysters not occur in high densities on bare substrata in the northeastern United States as found in the Southeast? These and other questions require a broader un

derstanding of oyster ecology in the Northeast, as the extension of oysters into the intertidal has implications on oyster harvesting, restoration, and

management, especially relative to climate change.

Acknowledgments

We thank the Weeks family for allowing us access to the shoreline at Weeks

Point and for providing a variety of ancillary information regarding oyster popula tions at this site. We also thank Chris Davis for helping us sample intertidal oyster populations near Newcastle, ME, and Dr. Roger Mann and an anonymous reviewer

for valuable comments on the manuscript. Funding for this research was provided in

part by a National Estuarine Research Reserve System Fellowship # NOS-OCRM

2006-2000469. The paper is issued as Contribution Number 448 from the Jackson Estuarine Laboratory and the Center for Marine Biology.

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