BEHAVIOR OF JUVENILE AMERICAN LOBSTERS, HOMARUS-AMERICANUS, UNDER PREDATION RISK

The influence of predation risk and food deprivation on the behavior a nd activity of juvenile American lobsters, Homarus americanus Milne Ed wards, was examined in single and paired individuals in laboratory exp eriments performed during 1988 and in the winter of 1991/92. In the pr esence of a predator (the tautog Tautoga onitis Linnaeus) restrained b ehind a barrier, single lobsters significantly reduced the time spent feeding at night, consumed fewer mussels, and quickly brought them bac k to shelter. Single lobsters did not forage during the day in any tre atment. If deprived of food for 60 h, they consumed more mussels and s pent more time walking than recently fed (12-h food-deprived) lobsters . Paired lobsters did forage during the day in the presence of a preda tor. The smaller lobsters (subdominant) in the pairs foraged for a lon ger time in the presence than in the absence of a predator and signifi cantly longer than single individuals. Shelter occupancy was significa ntly shorter in single? recently fed lobsters in the presence of a pre dator compared to time spent sheltering in its absence. Among food-dep rived lobsters? paired individuals spent a significantly shorter time within the shelter than single lobsters in the absence of a predator. Larger (dominant) lobsters, however, spent more time than subdominant lobsters within the shelter during all periods of the day. Without a p redator, paired lobsters spent significantly more time than single one s in shelter-related activities. Under predation risk, subdominant lob sters concentrated shelter-building time during the day and built a hi gher percent of alternative shelters than either single or dominant lo bsters. In the absence of a predator, paired lobsters walked in the op en area for a significantly longer time than single ones in the absenc e of a predator. This apparently was associated with fighting between dominant and subdominant lobsters and the attempts of the larger lobst er to drive the smaller one from its shelter. During the day, lobsters fought for a significantly longer time in the presence than in the ab sence of a predator. When the tautog was not constrained, mortality ra te was similar in both single and paired lobsters. Mortality rate amon g subdominant lobsters, however, was seven times higher than among dom inant lobsters. We suggest that the risk of predation interferes with the ability of single juvenile lobsters to acquire and consume food. T hey appear to trade off energetic consideration against risk of predat ion when foraging away from the shelter. The introduction of a conspec ific competitor to the system may further increase risk (of the subdom inant) to the predator. Intraspecific interactions tend to increase th e risk of predation to smaller lobsters but increase the survival rate among larger lobsters.