FISHERY BULLETIN: VOL. 87, NO. 1 



arthropods were found most frequently (64%) and 

 were predominantly (61%) small crustacean re- 

 mains. The occurrence of the blue mussels, crab 

 remains, and foraminifera in 2% of the stomachs in- 

 dicated that these were minor dietary components. 

 Algae was the dominant (69%) plant food; Spartina 

 occurred in only 4% of the stomachs. Unidentified 

 remains were found in 39% of the stomachs. Most 

 stomachs (75%) contained food, although 6% of 

 these were nearly empty. 



Lady Crab 



Animal foods were found in 94% of the lady crab 

 stomachs; none contained plant foods (Table 2). This 

 indicated a strictly carnivorous food habit. Of the 

 animal foods, moUusks were encountered more often 

 (78%) than arthropods (50%) or annelids (11%). Pele- 

 cypods occurred much more often (72%) than gas- 

 tropods (6%). Blue mussels found in 56% of the 

 stomachs were usually shell fragments; gem clams 

 were found in 17% of the stomachs, and one stom- 

 ach contained as many as 17. Other pelecypods 

 found in 22% of the stomachs were glossy-white 

 fragments (possibly Tellina sp.). Arthropod foods 

 encountered were crab (28%) and small crustacean 

 (17%) remains. The jaws of Nereis were found in 

 11% of the stomachs. Unidentified tissues occurred 

 in 22% of the stomachs. Although 58% of the lady 

 crab stomachs contained food, 6% of these were 

 nearly empty. 



Mud Crab 



Animal foods were found in 42% of the mud crab 

 stomachs; plant foods were in 21% (Table 2). This 

 indicated a predominantly carnivorous food habit 

 with herbivorous tendencies. Of the animal foods, 

 arthropods were more frequently (34%) encountered 

 than mollusks (3%) or annelids (3%). Small crusta- 

 ceans were found in 32% of the stomachs, and crabs 

 in 3%. Blue mussels were found in only 3% of the 

 stomachs and none contained gastropods. Fish re- 

 mains were found in only 3% of the stomachs. Of 

 the plant foods, algae was found in 16% of the 

 stomachs and Spartina in 8%. All of the stomachs 

 with food contained unidentified tissues. Although 

 69% of the mud crab stomachs contained food, only 

 8% of these were nearly empty. 



Spider Crab 



Animal foods were found in 42% of the spider crab 

 stomachs and plant foods in 75% (Table 2). This in- 



dicated a predominantly herbivorous food habit with 

 carnivorous tendencies. Of the animal foods, mol- 

 lusks occurred more often (25%) than arthropods 

 (8%). Pelecypods were found more often (25%) 

 than gastropods (8%). Blue mussels occurred in 

 17% of the stomachs. None of the stomachs con- 

 tained annelids. Of the plant foods, algae was found 

 in 67%, and Spartina was found in 25% of the 

 stomachs. Unidentified tissues were found in 58% 

 of the stomachs. Although 67% of the spider crab 

 stomachs contained food, 25% of these were near- 

 ly empty. 



DISCUSSION 



Food habits of the five crab species were generally 

 similar, a probable reflection of prey availability. 

 Blue, green, and mud crabs tended to be carnivorous 

 and spider crabs tended to be herbivorous, while 

 lady crabs were observed to be exclusively carniv- 

 orous. However, neither of the latter two species 

 was well represented (Table 2). Mollusks and arthro- 

 pods were frequent dietary components of the blue 

 and lady crab specimens (50% to 78%); such foods 

 were in 43% and 35% of the green crab stomachs 

 (Table 2). Many of the lady crabs (72%) and blue 

 crabs (49%) contained pelecypods, but only 31% of 

 the green crabs had eaten this food. 



Green crabs are the sole portunid in the decapod 

 fauna of Plum Island Sound, and Ropes (1968) found 

 mollusks in 75% of the stomachs examined, with 

 pelecypods (68%) the most frequent type of moUusk 

 eaten. At Pettaquamscutt River, the low occurrence 

 of pelecypods in green crab stomachs suggested that 

 interaction between portunid species may have been 

 affecting their feeding habits. Blue and lady crabs 

 are adept at swimming and may use this ability in 

 obtaining food and avoiding conflicts over food 

 items; green crabs may be at a disadvantage in com- 

 peting for food by their relatively poor swimming 

 abOities. Many blue crabs were larger than the green 

 or lady crabs taken, and their powerful claws may 

 have been of positive advantage in encounters with 

 other crabs. The high occurrence (40%) of crab re- 

 mains in blue crab stomachs suggests inter- or intra- 

 specific predation occurred, although the frag- 

 mented remains did not allow identification to 

 species. Lady crabs may also have exerted predator 

 pressure because 28% of their stomachs contained 

 crab remains. Crab predation by green crabs was 

 the lowest (4%) for the portunids examined and was 

 lower than reported by Ropes (1968) at Plum Island 

 Sound (13%). 



Small green crabs caught on 6 September 1955 



202 



