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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 intertidal
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 populations
in the same geography, and their sizes suggest a persistence of 5 or more years.
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 (less than 1–5.6 individuals/
m2) of detached populations, which suggested to them a potential
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 others
from the upper reaches of the Damariscotta River near Newcastle, ME
(Fig. 1). We hope that enhanced knowledge regarding these persistent intertidal
oyster assemblages will encourage future conservation, restoration, and
a better understanding of their ecology.
Our initial studies at Weeks Point, NH (43°03'32"N, 70°51'42"W) were
conducted during October 21, 2005 at which point we visually inspected a
1Jackson Estuarine Laboratory, 85 Adams Point, Durham, NH, 03824. 2Department
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 Program, Richmond,
VA 22901. *Corresponding author - email@example.com.
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 using
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 assumed
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 counted,
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°4'8.98", 70°51'45.68"W) and Woodman Point, Greenland,
NH (43°4'18.55"N, 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 occurrence
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.
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 of 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 Island,
ME. D) Close-up of Goose Rock intertidal oyster community; note barnacles,
mussels, and Ascophyllum.
212 Northeastern Naturalist Vol. 15, No. 2
mudflats. Oyster densities ranged from 10 to 150 individuals/m2, with a
mean density of 57 ± 40.8 individuals/m2 (standard deviation); they extended
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 regression,
oyster shell height was inversely related to tidal height (r2 = 0.62,
p = 0.007). No significant relationships were found between oyster metrics
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 canopies
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 (Linnaeus)
(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 habitats.
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.
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 stories
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 Ascophyllum
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 oysters
(<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 postsettlement
mortality limits their distribution.
The intertidal zone where Ascophyllum and Fucus vesiculosus L. (bladder
wrack) occur within the Great Bay estuarine system is estimated to be
130,000 m2 or 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 subtidal
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 understanding
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.
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 populations
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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