MECHANISMS OF PREDATION AMONG LARGE DECAPOD CRUSTACEANS OF THE GULF OF MAINE COAST - FUNCTIONAL VS PHYLOGENETIC PATTERNS

Diversity of form and function among phylogenetically related species causes us to question the widespread assumption that these species are likely to be ecologically similar. We studied four syntopic species of large decapod crustaceans which live in the shallow subtidal zones of the Gulf of Maine and feed on (among other things) the blue mussel, Mytilus edulis (Linnaeus). The decapods included an astacid lobster (Homarus americanus (Milne Edwards)) and three species of brachyuran crabs distributed between cancrid (Cancer irroratus (Say) and Cancer borealis (Stimpson)) and portunid (Carcinus maenas (Linnaeus)) families. Pair-wise multiple comparisons made across and within mussel size range treatments revealed that the two smaller species, (Carcinus maenas and Cancer irroratus) are similarly quicker, more dexterous, and capable of a greater diversity of shell opening tactics than the two larger species (Homarus americanus and Cancer borealis), which utilize only crushing tactics. These results and field observations suggest that a functional dichotomy exists between the smaller and larger pairs of decapods, which corresponds more to morphological and behavioral characteristics of the species than to their phylogenetic relationships.