Settlement-driven, multiscale demographic patterns of large benthic decapods in the Gulf of Maine

Three decapod species in the Gulf of Maine (American lobster Homarus americ anus Milne Edwards, 1837, rock crab Cancer irroratus Say, 1817, and Jonah c rab Cancer borealis Stimpson, 1859) were investigated to determine how thei r patterns of settlement and post-settlement abundance varied at different spatial and temporal scales. Spatial scales ranged. from centimeters to hun dreds of kilometers. Abundances of newly settled and older (sum of several cohorts) individuals were measured at different substrata, depths, sites wi thin and among widely spaced regions, and along estuarine gradients. Tempor al scales ranged from weekly censuses of new settlers within a season to in ter-annual comparisons of settlement strengths. Over the scales considered here, only lobsters and rock crabs were consistently abundant in their earl y post-settlement stages. Compared to rock crabs, lobsters settled at lower densities but in specific habitats and over a narrower range of conditions . The abundance and distribution of older individuals of both species were, however, similar at all scales. This is consistent with previous observati ons that, by virtue of high fecundity, rock crabs have high rates of settle ment, but do not discriminate among habitats, and suffer high levels of pos t-settlement mortality relative to lobsters. At settlement, large, habitat- scale differences exist for lobsters but not for rock crabs; these are prob ably the result of larval settling behavior. In contrast, patterns at the l argest, inter-regional, spatial scales suggest oceanographic control of lar val delivery. Increased mobility and vagility with greater body size for bo th species reduces demographic differences among older individuals over a r ange of spatial scales. (C) 1999 Elsevier Science B.V. All rights reserved.