DIFFERENT EARLY POSTSETTLEMENT STRATEGIES BETWEEN AMERICAN LOBSTERS HOMARUS-AMERICANUS AND ROCK CRABS CANCER IRRORATUS IN THE GULF-OF-MAINE

The abundance of many invertebrates with planktonic larval stages can be determined shortly after they reach the benthos. In this study, we quantified patterns of abundance and habitat utilization of early bent hic phases of the American lobster Homarus americanus and the rock cra b Cancer irroratus. These 2 decapods are among the most common and abu ndant macroinvertebrates in coastal zones of the Gulf of Maine, with s imilar densities of larger individuals. Settlement and early postsettl ement survival indicate that lobsters are highly substrate-specific ea rly in life, settling predominantly in cobble beds. Crabs appear to be less selective, setting both in cobble and sand. Cumulative settlemen t of crabs, inferred from weekly censuses over the summer, was an orde r of magnitude greater than that of lobsters over the same time period . However, only crabs showed significant postsettlement losses. Althou gh the identity of specific predators is unknown, predator exclusion e xperiments and placement of vacant uninhabited nursery habitat suggest ed that post-settlement mortality rather than emigration was responsib le for these losses. The selective habitat-seeking behavior and lower post-settlement mortality of lobsters is consistent with their lower f ecundity and later onset of reproductive maturity. The patterns observ ed for crabs, however, suggest a different strategy which is more in a ccordance with their higher fecundity and earlier onset of maturity. I t is possible that lower fecundity but greater per-egg investment, alo ng with strict habitat selection at settlement and lower post-settleme nt mortality, allows adult lobster populations to equal adult populati ons of crabs. This occurs despite crabs being more fecund and less hab itat-selective settlers but sustaining higher postsettlement mortality .