Foraging and shelter behavior of juvenile American lobster ( Homarus americanus): the influence of a non-indigenous crab

Adult green crabs are highly aggressive predators that exhibit fast population growth in newly invaded areas and potentially compete with juvenile lobsters for limited resources. Previous studies suggest that juvenile lobsters utilize shelter to avoid predation but shelter dependence decreases as they mature and develop predator defense mechanisms. Smaller lobsters must therefore trade-off energetic needs with predation risk. In laboratory experiments we examined how the presence of an adult green crab affects foraging and shelter behavior of juvenile lobsters (25–51 mm CL) by offering juvenile lobsters protective shelter and an adjacent food patch in the presence or absence of a green crab. For each trial we monitored lobster behavior over 8 h. Our results indicate that in the presence of a green crab, small juvenile lobsters (< 35 mm CL) spent significantly less time foraging and more time within the shelter. These small juveniles also spent significantly less time feeding and/or handling the food but took longer to actually locate the food source. In contrast, the presence or absence of a green crab did not have any influence on the results of trials that used juvenile lobsters over 35 mm CL. Thus, green crabs can significantly influence foraging and shelter usage of small (< 35 mm CL) juvenile lobsters and re-affirm the idea that this early stage represents the most vulnerable in the benthic life cycle of lobsters. ► Juvenile lobsters changed forage and shelter behavior in the presence of green crab. ► Lobsters foraged less and made fewer trips from it's shelter to the resource. ► Lobsters (< 35 mm CL) spent more time in shelter than larger sized juveniles. ► At 36 mm CL appears to be a shift from shelter use to increased foraging.