easily separated wliile the stomachs were ex- 

 amined because the old stomach is replaced just 

 before ecdysis. A second group included recently 

 molted crabs with very soft shells. The next two 

 groups, moderately soft-shelled and nearly hard- 

 shelled crabs, were separated on the basis of the 

 ease with which the carapace indented under 

 finger pressure. The carapaces of liard-shelled 

 crabs, the fifth grouj^, were rigid and cracked if 

 enough force was exerted. 



The food habits of premolt and recently molted 

 crabs were particularly affected (fig. 10). A few 

 of these crabs contained bits of shell presumably 

 ingested before ecdysis took place. Thus, like otliei' 

 brachyuran crabs (Waterman, 1960), green crabs 

 stop feeding just before and after ecdysis. 



Occurrence of food increased as the shells of 

 molted crabs progressively hardened. Most of the 

 moderately soft-shelled and nearly hard-shelled 

 crabs contained Gemma, Hydrohia, small arthro- 

 pods, and algae, and all of the typical foods were 

 found in both groups. All foods, except those men- 

 tioned for moderately soft -shelled crabs, occurred 

 more often and in larger numbers in nearly hard- 

 shelled crabs than in any other group. This finding 

 suggested that nearly hard-shelled crabs had a 

 greater appetite than hard-shelled crabs. Never- 

 theless, the total predation by hard-shelled crabs 

 was greater than that of nearly hard-shelled crabs 

 because the crabs are in the hard-shelled condi- 

 tion for a longer period of time (Waterman, 1960) . 



MATING 



Stomach analysis of a few male crabs, each 

 caught clasping a female, indicated that they 

 ceased feeding during the mating act. Only 2 of 

 the 10 mated males from Plum Island Kiver con- 

 tained food, and both were nearly empty. No mated 

 pairs were caught at Luf kins Flat. 



THE GENERAL PREDATORY 

 ECOLOGY OF GREEN CRABS 



Green crabs eat other foods than those listed 

 in table 1. I collected stomachs from Maine which 

 contained Anomia sp., whereas Aquipecten it^acli- 

 ans and Zostera iiuirina occurred in some from 

 Rhode Island. Spear = found during a laboratory 



^ Spear, Harlan S. 1955. Notes on laboratory experiments on 

 feeding habits of green crabs. [U.S.] Fish Wildl, Serr., Clam 

 Invest., Boothbay Harbor, Maine, 5th Conf. Clam Res. : 45. 

 [Mimeographed.] 



Study that green crabs ate small hard clams, Mer- 

 cenarla mercenarla (6-10 mm.), in j:) reference to 

 larger ones (20-25 mm.). Green crabs almost de- 

 stroyed small hard clams planted experimentally 

 in Wickford Harbor, R.I., by Warren S. Landers 

 (oral communication). Dearborn'^ found the fol- 

 lowing foods acceptable to green crabs : C rassostrea 

 nirginica, Astarte castanea, Pectin grandis ( = 

 Placopecten magellanicus) , NiKula sp.. Modiolus 

 modiolus, Callocardia {=Pitar) morrhuana, Spis- 

 ula soltdissima, Saxicava {=Hiatella) arctica, 

 Fundulus sp., Laminaria sp., Littorina Uttorea, 

 and L. ohtusata. Such variety in the diet of green 

 crabs is undoubtedly due to their omnivorous feed- 

 ing habits. 



The green crab's ability to grasp, crush, and 

 tear apart food probably permits scavenging for 

 foods such as dead fish; however, they are not 

 exclusi^'ely scavengers because they eat many live 

 foods and may actually prefer fresh food to car- 

 rion. Fishermen replace old decomposed bait be- 

 cause they say fresh bait catches more green crabs. 

 Some fresh, recently killed food is available from 

 natural causes. While using free diving gear, I 

 saw green crabs quickly pick up and eat small 

 herring that sank to the bottom after being killed 

 or stunned by gulls. 



Sami^les of ci-abs taken by traps or dredges or 

 from bank caves indicated that the population of 

 green crabs in Plum Island Sound was large. Evi- 

 dence of intraspecific competition was meager, 

 however, even though the foods eaten by all sizes 

 of crabs were qualitatively similar. The incidence 

 of cannibalism, a possible measure of extreme com- 

 petition, was low. Actually there was more reason 

 to suppo.se that intraspecific comi^etition was cir- 

 cumvented. Small crabs, which would be the most 

 \'ulnerable to cannibalism because of their size, did 

 not mix with the large crabs. Presumably tlie sep- 

 aration of small from large crabs enabled them to 

 grow and develoj^ their food-gathering abilities 

 without the necessity of competing with large 

 crabs. The omni^'orous feeding of green crabs also 

 serves to reduce intraspecific competition and to 

 permit a large population to inhabit an area. 



Predator control methods, developed during in- 

 vestigations of the decline in soft-shell clams, re- 

 duced the effects of green crabs on the clam flats. 

 Fences (Smith, 1954; Smith et al., 1955) and 



» Footnote 1. 



FEEDING HABITS OF GREEN CRAB 



199 



