MACROFAUNAL COMMUNITIES WITHIN AND ADJACENT TO A DETRITUS-RICH SUBMARINE-CANYON SYSTEM

Macrofaunal abundance, biomass, diversity and species assemblages with in Scripps and La Jolla Submarine Canyons are compared with those on t he nearby continental shelf and slope. Our primary objective was to ex amine the effect of detrital aggregates on infaunal communities within canyons, Two submarines, a remotely operated vehicle (ROV), and a Sou tar box-corer were used to collect samples. Within the canyons, organi c enrichment by macrophyte detritus was evident from canyon heads down to 550 m, and evidence of strong currents (coarse sediment) was found down to 700 m, Infaunal density and biomass were higher in the canyon s than outside at all depths where comparative data were available (10 0-500m). Infaunal assemblages in canyons were distinct from those at r eference stations. Both the canyon and non-canyons samples showed comm unity differentiation with depth. Species diversity was generally high , but decreased with depth outside of canyons and increased with depth within the canyons. Low diversity at shallow depths within the canyon is attributed to a combination of organic enrichment and physical dis turbance. Submarine canyons are commonly found to contain distinct spe cies assemblages or higher faunal densities and/or biomass than nearby non-canyon regions at similar depths. Canyons are regular features al ong most ocean margins and appear to be important as sites of enhanced secondary production, provide diverse habitats, and act as conduits o f coastal detritus to the deep-sea. (C) 1998 Elsevier Science Ltd. All rights reserved.