THE FOOD HABITS OF FIVE CRAB SPECIES AT PETTAQUAMSCUTT 



RIVER, RHODE ISLAND 



John W. Ropes^ 



ABSTRACT 



The stomach contents of five crab species— green crab, Carcinus maenas; blue crab, Callinectes sapidity; 

 lady crab, Ovalipes oceilatus; mud crab, Neopanope texana; and spider crab, Libinia emarginata—viere 

 examined from collections made in the Pettaquamscutt River, Rhode Island, during 1955-57. A car- 

 nivorous food habit characterized all species, although spider crabs contained plant foods more often 

 than animal foods. Mollusks (especially pelecypods) and arthropods were frequent dietary components 

 of the green, blue, and lady crabs. Intense predation on small, recently set pelecypods was indicated. 

 The three species of portunid crabs (green, blue, and lady) appeared to have similar food habits, sug- 

 gestive of potential interspecific competition for food. Crab remains were most frequently encountered 

 in blue crab stomachs; lady crabs contained this food more often than green crabs. Small Crustacea and 

 plant foods occurred more often than hard-shelled foods and with equal frequency in the stomachs of 

 small green crabs (<20 mm carapace width). 



Predation by crabs has been identified as a serious 

 threat to successful management of commercial 

 bivalve resources (Carriker 1967; R. N. Hanks 1963; 

 R. E. Hanks 1969). Many studies have concentrated 

 on the green crab, Carcinus maenas, because of its 

 abundance, its extensive distribution in the coastal 

 zone of northeastern United States and Canada and 

 Europe, and its predation on bivalves, especially the 

 soft-shelled clam, Mya arenaria. Ropes (1968) and 

 Welch (1968) have provided extensive reviews of the 

 U.S. literature on this species; Davies (1966) and 

 Kitching et al. (1959) have reported on its effects 

 on European or blue mussel, Mytiltcs edulis, culture. 

 Blue crabs, Callinectes sapidus; lady crabs, Ovalipes 

 oceilatus; and mud crabs, Neopanopeus texana, have 

 also been found to be predators of bivalves (Ryder 

 1884; Hay 1905; Fowler 1911; Belding 1930; Anon. 

 1941; Lunz 1947; Turner 1948; Bulter 1954; Landers 

 1954; Dunnington 1956; Darnell 1958, 1959; McDer- 

 mott 1960; Galtsoff 1964; Loosanoff 1965). Many 

 of these studies described the relationship between 

 a particular predator and prey. 



After completing collection and examination of 

 green crab stomachs from Plum Island Sound, MA, 

 I foimd that four of the species mentioned above and 

 the spider crab, Libinia emarginata, could be col- 

 lected from a fairly restricted area at the mouth of 

 the Pettaquamscutt River, RI. This was an oppor- 



'Northeast Fisheries Center Woods Hole Laboratory, National 

 Marine Fisheries Service, NOAA, Woods Hole, MA 

 02543. [Deceased September 1988.] 



Manuscript accepted October 1988. 

 Fishery Bulletin 87:197-204. 



tunity to examine possible inter- and intraspecific 

 feeding habits by sympatric decapod crustaceans. 

 The taxonomic relationship and morphological dif- 

 ferences of the three portunid crabs (blue, green, 

 and lady crabs) suggested making comparisons of 

 stomach contents with each other and the two other 

 crab species to determine the potential for preda- 

 tion on bivalves and to observe possible similarities 

 and differences in their diets. The impact of such 

 predation on bivalves of commercial importance has 

 practical implications for resource management. 



METHODS 



From 1955 through 1957, crabs were collected 

 during daylight hours from three subtidal areas of 

 Pettaquamscutt River, RI, (Fig. 1) by towing a scal- 

 lop dredge from a 12 ft aluminum boat powered by 

 an 18 hp outboard motor (see Ropes [1968] for a 

 description of the dredge). Intertidal areas were 

 limited by the sharply sloping marsh banks which 

 could not be sampled by the dredge. Thus, tows were 

 made subtidally over shoal bars, along the edges of 

 bars in the channel, and near the banks of the river. 

 All samples were taken during ebb tide and before 

 low water because experience at Plum Island Sound 

 had shown that green crabs were actively moving 

 about at that time. In 1955, five collection trips were 

 made in July, September, and October; in 1956, six 

 trips were made from May through August; and in 

 1957, nine trips were made in August through Oc- 

 tober (Table 1). At the laboratory, the species and 



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