2009 NORTHEASTERN NATURALIST 16(3):481–487
Use of Subtidal Habitat by the Asian Shore Crab
Hemigrapsus sanguineus in Long Island Sound
Michael Gilman1,2,* and Sean Patrick Grace2
Abstract - Hemigrapsus sanguineus Asian Shore Crab is an introduced but now
common crab found intertidally along the Connecticut coastline. Little is known of
its subtidal occurrence. This species was found to be seasonally abundant subtidally,
at depths varying from 1.3–3.9 m, during a 2-year study conducted within a commercial
marina in Clinton Harbor, CT. Hemigrapsus sanguineus was trapped at three
subtidal locations, with highest concentrations observed during the winter. A total of
2020 crabs were caught: 1255 males, 741 females, and 24 crabs that were 9 mm or
smaller and sexually indistinguishable. Large males with carapace widths between
45–48 mm were captured at all three locations. These sizes are among the largest
reported for this species. This work documents year-round use of subtidal habitat by
Asian Shore Crab in Long Island Sound.
Introduction
Hemigrapsus sanguineus (Varunidae) (de Haan) (Asian Shore Crab) was
first reported on the east coast of North America in September 1988, in Cape
May County, NJ (Williams and McDermott 1990). Since its introduction,
Asian Shore Crab has become the dominant intertidal crab species along
the shores of Connecticut and southern New England (Ahl and Moss 1999,
Brousseau et al. 2002, Kraemer et al. 2007, Ledesma and O’Connor 2001,
Lohrer and Whitlach 1997).
Past studies on the intertidal behavior of Asian Shore Crab have demonstrated
that this species can exploit different, but overlapping habitats on
cobble or boulder shores in rocky intertidal habitats (Fukui 1988). In addition,
Asian Shore Crab has managed to overpopulate and displace the earlier invasive
Carcinus maenas (L.) (Green Crab), from Long Island Sound intertidal
zones (Ahl and Moss 1999, Kraemer et al. 2007, Lohrer and Whitlach 1997).
Very little literature exists that describes the use of any subtidal habitat
by Asian Shore Crab. However, McDermott (1998, 2007) and Kraemer et al.
(2007) have speculated about Asian Shore Crab subtidal migration during the
winter months. McDermott (2007) identified various species of subtidally occurring
epibionts recruiting on Asian Shore Crab carapaces, while Kraemer
et al. (2007) observed the disappearance in winter and sudden reappearance
in summer of larger adult Asian Shore Crabs in the intertidal. These findings
indicate that Asian Shore Crab does spend periods of time subtidally. The goal
of this study was to determine if Asian Shore Crab was a member of the subtidal
community within Cedar Island Marina, Clinton Harbor, CT.
1Cedar Island Marina Research Lab, PO Box 181, Clinton, CT 06413. 2Southern
Connecticut State University, 501 Crescent Street, New Haven, CT 06513.
*Corresponding author - gilmanm2@southernct.edu.
482 Northeastern Naturalist Vol. 16, No. 3
Methods
Three unbaited 0.75-m2 traps with 4-cm mesh (Fig. 1) were placed at
three sites (1 trap/site) within Cedar Island Marina (41°16'N, 72°32'W).
Traps were not baited so as to not attract predatory species that could possibly
dissuade Asian Shore Crabs from entering. All trap sites were accessible
by marina docks and were labeled corresponding to their locations within
Clinton Harbor. These were Inner Harbor (IH), Middle Harbor (MH), and
Outer Harbor (OH) (Fig. 2). Mean depth (m) of each site was measured to
the closest 0.5 m with a weighted line and calculated once throughout the
study period during a single spring high and low tide. Each value is the mean
of one high and one low tide measurement. Mean depths were 2.45 m (OH),
3.13 m (MH), and 2.29 m (IH). The substrate around Cedar Island Marina is
mostly silt-clay (43–95%), with little solid substrate present due to the semiannual
dredging (DeSanto 1987).
Data were collected weekly from January 2005 through October 2006,
except for September and October of 2005, when sampling was not possible.
All traps were checked consecutively on the same day. On every
sampling day, each trap was emptied of all organisms. Asian Shore Crabs
were sexed, and carapace width (CW) measured to the nearest millimeter.
Sexual maturity was based on previous findings by Fukui (1988) and Lohrer
and Whitlach (1997). These studies found that male Asian Shore Crabs reach
sexual maturity at approximately 19.0 mm CW (Fukui 1988) and females at
Figure 1. Photograph of the trap used to capture Hemigrapsus sanguineus (Asian
Shore Crab).
2009 M. Gilman and S.P. Grace 483
12 mm (Lohrer and Whitlach 1997). Traps were regularly power-washed to
remove all sessile fouling organisms.
Results
During the two-year duration of this study, a total of 2020 Asian Shore
Crabs were caught. The number of crabs caught per month varied throughout
the seasons (Fig. 3). However, there was never a month where no crabs were
captured. When combined, February, March, and April of both years account
for 64% (n = 1297) of the total catch, while the summer months of June,
July, and August account for only 7% (n = 137) of the total catch. The total
number of Asian Shore Crabs caught differed between sites, with the greatest
number corresponding with the deepest site. The total numbers of crabs
caught per site were: Inner Harbor (n = 245), Middle Harbor (n = 1231), and
Outer Harbor (n = 545).
Sixty-two percent (n = 1255) of the total catch were male, while 37% (n =
741) were female. Due to the inability to distinguish between sexes of Asian
Shore Crabs 9 mm and below, 24 crabs were not sexed. The overall ratio of
males to females was 1.7:1 (n = 1996), while the IH (n = 245) and MH (n =
1231) traps both had a male to female ratio of 1.5:1, and OH (n = 545) had
a 2:1 male to female ratio.
Eighty-eight percent (n = 1127) of the males were sexually mature at
19.0 mm CW or above (Fukui 1988), while 98% (n = 733) of the females
caught were mature, at 12.0 mm CW or above (Lohrer and Whitlach 1997).
Twenty-six ovigerous females were caught during this study with the smallest
at 16 mm CW. All ovigerous females were recorded between the months
of April and September during both years.
Figure 2. Map of Clinton Harbor, Long Island Sound (41°16'N, 72°32'W). Traps (1 trap/
site) were located at Inner Harbor (IH), Middle Harbor (MH), and Outer Harbor (OH).
484 Northeastern Naturalist Vol. 16, No. 3
The majority of the total catch (n = 1745) were larger than 18 mm CW
and considered to be sexually mature. A smaller number (n = 64) were ≥40
mm CW, and the largest crab was a male with 48 mm CW. The largest female
captured was 40mm CW. Each of these crabs have carapace widths among
the largest reported for both genders. In fact, they are larger than what was
previously considered to be the maximum size for each sex reported by Fukui
(1988): 42 mm (male) and 39 mm (female).
Other crab species caught during the study period were Carcinus maenas
(L.) Green Crab (n = 1369), Panopeus herbstii (H. Milne Edwards)
(Mud Crab; n = 45), Libinia emarginata (Leach) (Spider Crab; n = 250),
Eurypanopeus depressus (S.I. Smith) (Mud Crab; n = 175), and Callinectes
sapidus (M.J. Rathbun) (Blue Crab) (n = 94). Green Crab was the secondmost
abundant species of crab (n = 1369). As with Asian Shore Crab, the
Figure 3. Total catch of Asian Shore Crab around Cedar Island Marina separated by
gender into three size classes (0–18 mm, 19–30 mm, and ≥31 mm CW).
2009 M. Gilman and S.P. Grace 485
number of Green Crabs caught differed with location: Inner Harbor (n =
513), Middle Harbor (n = 279), and Outer Harbor (n = 577).
Discussion
This study documents the subtidal occurrence of the Asian Shore Crab
within a marina in Clinton Harbor, CT, Long Island Sound. Abundance varied
seasonally, with the fewest crabs caught during June through August, and most
caught during February through April. McDermott (1998, 2007) and Kraemer
et al. (2007) have both speculated that Asian Shore Crab migrates to the subtidal
during the winter months and back to the intertidal during the summer
months. Data from this study support this idea.
Many factors may contribute to why Asian Shore Crab was captured in
highest numbers at the deepest depth of the study site during the winter. The
Cedar Island Marina is a basin, reaching its deepest point in a man-made
channel running parallel to the marina. Depth range of the channel is 8.5 m
at low tide to 13.5 m at high tide. In this study site, the Middle Harbor trap
was the closest in relation to the channel. It is possible that Asian Shore
Crab were moving into these subtidal depths for winter refuge and protection
against the elements.
The source of the population of Asian Shore Crab is not known. There are
no rocky intertidal sites in close proximity to the subtidal area where the study
was conducted. The closest intertidal area is approximately 0.4 km (0.25 mi)
away and devoid of a rocky habitat. The closest rocky intertidal zone is approximately
3.2 km (2 mi) away from the study site. The possibility does exist,
however, that Asian Shore Crabs are traveling large distances to this subtidal
habitat. Brousseau et al. (2002) demonstrated that the Asian Shore Crab is a
highly mobile species with very low site fidelity in the intertidal.
The occurrence of Asian Shore Crabs at Cedar Island Marina is unexpected
given what is known about the shelter requirements of this species.
Asian Shore Crabs on both US coasts do not inhabit flat, open areas of
sand or mud that lack suitable shelters (Jenson et al. 2002). Although the
seabed within Cedar Island Marina is a predominately flat, silt/clay habitat
(DeSanto 1987), the docking structures of the marina may act as shelter for
these crabs. These structures attract motile and sessile organisms that could
also serve as a food source. Asian Shore Crabs consume many recruiting
species observed growing on the marina structures. These include Mytilus
edulis L. (Blue Mussel; DeGraaf and Tyrrell 2004), Crassostrea virginica
(Gmelin) (Eastern Oyster; Brousseau et al 2001), Semibalanus balanoides
(L.) (Barnacle; Brousseau and Goldberg 2007), and macroalgal species such
as Enteromorpha spp. and Chondrus crispus (L.) J. Stackhouse (Brousseau
and Baglivo 2005).
Five other species of crab were caught during this study; Green Crab,
Mud Crab, Flatback Mud Crab, Spider Crab, and Blue Crab share the same
subtidal habitat within this study site. How these species affect each other’s
abundance is unknown. Perhaps Asian Shore Crab has the same affect on
486 Northeastern Naturalist Vol. 16, No. 3
Green Crab in the subtidal as has been well documented in the intertidal
(Jenson et al. 2002). Interestingly, the abundance of Green Crab differed in
inverse proportion to the Asian Shore Crab. The Asian Shore Crab was most
abundant in the Middle Harbor (n = 1231) followed by the Outer Harbor (n =
545) and the Inner Harbor (n = 245). In contrast, the Green Crab was most
abundant in the Outer Harbor (n = 577) and the Inner Harbor (n = 513), while
the lowest abundance was recorded in the Middle Harbor (n = 279).
Our study documents the presence of the invasive Asian Shore Crab in a
subtidal site in Long Island Sound. In addition, we have documented crabs of
each gender that represent some of the largest carapace widths ever recorded
for the species. Asian Shore Crab has been well documented in the intertidal
zones of Long Island Sound (Ahl and Moss 1999, Brousseau et al. 2002, Kraemer
et al. 2007, Ledesma and O’Connor 2001, Lohrer and Whitlach 1997);
however, until now, their subtidal existence has been only speculation. Numerous
studies are needed in order to gauge the full subtidal range of Asian
Shore Crab and the effects it may be having on other benthic organisms.
Acknowledgments
We thank Jeffrey Shapiro along with all other employees of Cedar Island Marina
for providing all needed dock space, materials, and encouragement. H. Craig, B.
Patrizzi, and T. Massari were extremely helpful in analyzing and collecting data. We
also thank R. Goldberg, K. Heinonen, T. Trott, G. Kraemer, and all anonymous reviewers
for recommendations and commentary on earlier drafts of this manuscript.
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