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Use of Subtidal Habitat by the Asian Shore Crab Hemigrapsus sanguineus in Long Island Sound
Michael Gilman and Sean Patrick Grace

Northeastern Naturalist, Volume 16, Issue 3 (2009): 481–487

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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. Literature Cited Ahl, R.S., and S. P. Moss. 1999. Status of the nonindigenous crab, Hemigrapsus sanguineus, at Greenwich Point, Connecticut, Northeastern Naturalist 6:221–224. Brousseau, D.J., and J.A. Baglivo. 2005. Laboratory investigations of food selection by the Asian Shore Crab, Hemigrapsus sanguineus: Algal versus animal preference. Journal of Crustacean Biology 25:130–134. Brousseau, D.J., and R. Goldberg. 2007. Effect of predation by the invasive crab Hemigrapsus sanguineus on recruiting barnacles Semibalanus balanoides in western Long Island Sound, USA. Marine Ecology Progress Series 339:221–228. Brousseau, D.J., A. Filipowicz, J.A. Baglivo. 2001. Laboratory investigations of the effects of predator sex and size on prey selection by the Asian crab, Hemigrapsus sanguineus. Journal of Experimental Marine Biology and Ecology 262:199–210. Brousseau, D.J., J.A. Baglivo, A. Filipowicz, L. Sego, and C. Alt. 2002. An experimental field study of site fidelity and mobility in The Asian Shore Crab (Hemigrapsus sanguineus). Northeastern Naturalist 9:381–390. DeGraaf, J.D., and M.C. Tyrrell. 2004. Comparison of the feeding areates of two introduced crab species, Carcinus maenas and Hemigrapsus sanguineus, on the Blue Mussel, Mytilus edulis. Northeastern Naturalist 11(2):163–167. DeSanto, R.S. 1987. Biogeographical survey and standing crop assessment. The biological diversity, productivity, and environmental compatibility of a small boat marina. Technical Report. DeLeuw, Cather, and Co., East Hartford, CT. 2009 M. Gilman and S.P. Grace 487 Fukui, Y. 1988. Comparative studies on the life history of the grapsid crabs (Crustacea, Brachyura) inhabiting intertidal cobble and boulder shores. Publication of the Seto Marine Biology Laboratory 33:121–162. Jenson, G.C., S.P. McDonald, and D.A. Armstrong. 2002. East meets west: Competitive interactions between Green Crab Carcinus maenas, and native and introduced shore crab Hemigrapsus spp. Marine Ecology Progress Series 225:251–262. Kraemer, G.P, M. Sellberg, A. Gordon, and J. Main. 2007. Eight-year record of Hemigrapsus sanguineus (Asian Shore Crab) invasion in western Long Island Sound Estuary. Northeastern Naturalist 14:207–224. Ledesma, M.E., and N.J. O’ Connor. 2001. Habitat and diet of the non-native crab Hemigrapsus sanguineus in southeastern New England. Northeastern Naturalist 8:63–78. Lohrer, A.M., and R.B. Whitlach. 1997. Ecological studies on the recently introduced Japanese Shore Crab (Hemigrapsus sanguineus), in Eastern Long Island Sound. Pp. 49–60, In N.C. Balcom (Ed.). Proceedings of the 2nd Northeast Conference on Nonindigenous Aquatic Nuisance Species. Connecticut Sea Grant College, University of Connecticut, Groton, CT. McDermott, J.J. 1998. The western Pacific brachyuran (Hemigrapsus sanguineus: Grapsidae) in its new habitat along the Atlantic coast of the United States: Geographic distribution and ecology. ICES Journal of Marine Science 55:289–298. McDermott, J.J. 2007. Ectosymbionts of the non-indigenous Asian Shore Crab, Hemigrapsus sanguineus (Decapoda: Varunidae), in the western North Atlantic, and a search for its parasites. Journal of Natural History 41:2379–2396. Williams, A.B., and J.J. McDermott. 1990. An eastern United States record for the Indo-Pacific crab, Hemigrapsus sanguineus (Crustacea: Decapoda: Grapsidae). Proceedings of the Biological Society of Washington 103:108–109.