ABSTRACT: The roles of nutrition, predation, and habitat choice were tested as mechanisms for shaping natural distribution of newly settled queen conch in seagrass Thalassia testudinum meadows in the central Bahamas. Small animals from 3 size classes were enclosed at 2 sites in 3 different habitats across a seagrass gradient (bare sand, low-density seagrass, medium-density seagrass) for 3 wk. Medium (11 mm shell length) and large (22 mm) newly settled conch grew faster in both seagrass habitats than on bare sand, but differences were not significant for small (5 mm) conch. Small and medium conch grown on sand, however, weighed more than those of the same length grown in seagrass. In laboratory habitat-choice experiments, newly settled conch preferred living seagrass and seagrass detritus over bare sand. Medium conch tethered in the 3 habitats at both sites suffered very high mortality (50 to 96% killed in 11 d), with those tethered in medium-density seagrass showing an advantage. Juvenile conch over 1 yr old are primarily associated with medium-density seagrass, but younger animals have been observed on sand. Results from this study show that nutrition is adequate on sand for newly settled conch, but an ontogenetic shift from sand into seagrass is unlikely because predation occurs before food becomes limiting or a habitat choice can be made. Nevertheless, post-settlement mortality is high regardless of where conch settle in the seagrass gradient, and predation is the most important mechanism influencing distribution.

KEY WORDS: Strombus gigas . Bahamas . Habitat complexity . Habitat choice . Predation . Seagrass . Tethering

Published in MEPS Vol. 123 (1995) on July 20
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1995