Predation by green crab and sand shrimp on settling and recently settled American lobster postlarvae

Abstract

Very little is known about predation on early life stages of the American lobster, Homarus americanus Milne Edwards, 1837, including the identity of predators and the threat they represent. In this laboratory experiment, we investigated the predatory threat that green crabs, Carcinus maenas (Linnaeus, 1758), and sand shrimp, Crangon septemspinosa Say, 1818, represent to settling and recently-settled lobster postlarvae. Lobster survival within 48 hours varied between 80-100% in control aquaria. In contrast, survival was only 40-60% in the presence of sand shrimp and 0-20% in the presence of green crab. Some sand shrimp were observed successfully catching and preying upon lobster as they were exploring the substrate for settlement, whereas green crab seem to have captured lobsters after they had adopted a benthic mode of existence. Since both of these predators commonly inhabit shallow cobble-bottom habitat where lobster settlement occurs, they could be important predators of young lobsters. Given these findings, we believe that future research should undertake the challenging task of confirming predation by green crab and sand shrimp on young lobsters in nature, and we suggest that molecular analysis of predator gut contents is the most promising approach to this question.