■,.'>. . 



ve 







The gastropod, Polinices duplicatus (shell approximately 8 cm in width), bulldozing 

 through the sediments in search of molluscan prey. Photo by P. Auster, University of 

 Connecticut. 



This species is found in estuaries and its 

 distributional pattern varies seasonally, 

 with the sexes, and with the stage of 

 development of the crab (Van Engel 1958). 

 Virnstein (1977) has documented the impact 

 of this species on the benthic infauna of 

 Chesapeake Bay. Blue crabs are voracious 

 predators as well as active diggers in the 

 sediment and can significantly alter both 

 species composition and abundance of the 

 infauna. The rock ( Cancer i rroratus ) and 

 Jonah (C^. boreal is ) crabs, commonly found 

 in estuaries on mud bottoms and rocky out- 

 crops respectively, are more often found 

 intertidally in northern New England than 

 in southern New England (MacKay 1943) and 

 probably have similar effects upon the 

 infauna as the blue crab. 



In spring, Li mulus po lyphemus , the 

 horseshoe crab, appears intertidally to 

 initiate spawning activities. These crabs 

 dig distinctive pits about 3 to 6 cm (1 to 

 2 inches) deep on the sediment surface 



while searching for bivalves and polychae- 

 tes. VJoodin (1978) demonstrated that this 

 digging activity reduced the abundance of 

 several infaunal invertebrates on a Mary- 

 land tidal flat. She noted that high 

 spring-summer densities of Limulus re- 

 sulted in feeding pits that covered 50% to 

 70% of her study site. New England popu- 

 lations of Limulus are not as large and 

 tend to be more spatially variable than 

 those described in Maryland. Occasionally 

 this species is used as bait for eel fish- 

 eries and uncontrolled harvesting may have 

 led to reduced population levels in some 

 New England areas. 



Several other species of 

 also frequent tidal flats, 

 shrimp, Palaemonetes pugio, 

 found in southern than in 

 England eelgrass beds. The 

 Crangon s eptemspinosus , i n 

 the only common shallow-water 



crustaceans 



The grass 



is more often 



northern New 



sand shrimp, 



contrast, is 



species 



between Cape Ann and the Bay of Fundy. 



24 



