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Cassanova, T., 2001. The Ecology of the Japanese Shore Crab (Hemigrapsus sanguineus De Haan) and its Niche Relationship to the Green Crab (Carcinus maenas Linneus) along the Coast of Connecticut, USA, Cedar Island Marina Research Laboratory. Proceedings of the Second International Conference on Marine Bioinvasions, New Orleans, La., April 9-11, 2001, pp. 16-17. The Ecology of the Japanese Shore Crab (Hemigrapsus sanguineus De Haan) and its Niche Relationship to the Green Crab (Carcinus maenas Linneus) along the Coast of Connecticut, USAThe intentional or accidental introduction of exotic species into North America is a great threat to the integrity of natural communities of plants and animals and to the preservation of endangered species (Carlton 1995). The effects of exotic species in marine systems have not been as well studied, but are potentially of such a magnitude that they may result in profound ecological changes in the structure of ocean communities (Carlton and Geller 1993). Long Island Sound has a long history of maritime commerce and it is likely that its species composition changes yearly because of the release of exotic species that are likely increasing yearly (Carlton 1985). Hemigrapsus sanguineus is now well established and rapidly expanding its range along the Atlantic coast of the United States from Chesapeake Bay to Cape Cod (Carlton 1995). Williams and McDermott (1990) first recorded H. sanguineus in the United States on 24 September 1988 during an invertebrate biology course field trip at Townsends Inlet, Cape May County, New Jersey [39º07'06" N70º43'00"W]. Twenty months later (28 May 1990) an immature female was recovered (McDermott 1991). This second finding suggested that the first record of the species in New Jersey was representative of a population already established in U.S. waters. This discovery provides a unique opportunity to document a major introduction to U.S. waters (McDermott 1991). H. sanguineus is now extremely abundant on the Connecticut coastline. H. sanguineus is thought to exploit different, but overlapping habitats with the green crab (Carcinus maenas Linnaeus) on cobble and boulder shores in rocky inter- tidal habitats (Fukui 1988). In areas where the green crab (C. maenas), used to be abundant, H. sanguineus is the most common observed species. Changes in abundance and/or distribution may be the result of inter-specific competition between the two species for food and habitat. The focus of this study was to determine the relative abundance of H. sanguineus at two specific sites on the Connecticut coastline. The possible inter-specific competition between H. sanguineus and C. maenas was determined through studying each species' population density and distribution along the rocky intertidal zone at eachsite. Two study sites were selected based on their central locality along the Connecticut shore and the large percentage of rocky intertidal shoreline, which C. maenas and H. sanguineus seem to prefer. The two sites chosen were Outer Island, Stony Creek and Hammonasset State Park, Madison Three transects were laid out at each sampling site delineating each tidal zone: the high intertidal zone, middle intertidal zone, and low intertidal zone. Each transect ran parallel to the water line. At Outer Island and Hammonasset State Park each transect was divided into quadrats measuring 1m 2 . The location of these stations was marked with stakes and through marking specific boulders with paint. Five quadrats at each station were randomly selected for each sampling period at Hammonasset State Park; at Outer Island, each quadrant was sampled at each sampling period. At each station, all the boulders within the quadrat to the underlying gravel within a depth of approximately 5 cm were turned over to hand capture both H. sanguineus and other native crab species including C. maenas. Crabs were placed in labeled jars upon capture and field preserved in a 10% buffered formalin solution until analyzed. The number of crabs for each species recovered from each quadrat was determined. Each crab species was identified and measured to the nearest 0.1mm with vernier calipers. Each crab species was recorded as a member of relative size categories determined by Yasuo Fukui (1988): less than 9mm were considered juveniles, 9.1mm-18.0mmÐsmall, and 18.1+mm-large (adult). Crabs were then sexed and ovigerous females were determined. Temperature and salinity for each sampling period at each site were recorded at the beginning of the sampling period using a YSI salinometer. Results presented clearly showed that H. sanguineus was numerically dominant in most areas of the intertidal zone at the sites studied. C. maenas were observed but in extremely low numbers at both sampling sites where historical data indicates they were once abundant. No other crab species were found at either Outer Island or Hammonasset within the sampling areas used for the duration of the study. H. sanguineus were found in areas of very high concentrations of amphipods throughout the mid and low tidal zones, although whether they had been using these amphipods as a food source is unknown. In areas of dense Fucus sp. cover, no medium-to-large male and female size classes of H. sanguineus were found. However, C. maenas were present in Fucus sp. occupied areas. The highest total numbers of H. sanguineus were distributed from the low to the mid tidal zone at both sampling sites for the May and June sampling periods. A spatial shift towards the mid tidal range was observed during July, August and September sampling periods where numbers were extremely high. For the same period, numbers of crabs in the lower tidal zone decreased. If this is a result of the colder water temperatures in September, the largest number of crabs in each size class would shift to higher zones. Male and female crabs of the larger class sizes showed little or no spatial preference for any portion of the intertidal region during any sampling period. There were no differences between larger crab sizes and sex (male vs. female), however in the smaller size classes, males were numerically dominant early in the year with females becoming dominant towards September. There were small correlations between smaller size classes and rock sizes, varying between 80-100mm. Literature Cited: Carlton, J.T. 1995. Marine invasions and the preservation of coastal diversity, endangered species. Update 12:4&5. Carlton, J.T. and J.B. Geller. 1993. Ecological roulette: the global transport of nonindigenous marine organisms. Science 261: 78-82. Fukui, Y. 1988. Comparative studies on the life history of the grapsid crabs (Crustacea, Brachyura) inhabiting intertidal cobble and boulder shores. Publications of the Seto Marine Biological Laboratory, 33: 4/6. McDermott, J.J. 1991. A breeding population of the western pacific crab Hemigrapsus sanguineus (Crustacea:Decapoda:Grapsidae) established on the Atlantic coast of North America. Biological Bulletin 181: 195-198.
Contact: Tara Casanova, Cedar Island Marina Research Laboratory, Clinton, CT 06413, USA |