Abyssal benthos of the Venezuela Basin, Caribbean Sea: standing stock considerations

Abstract

Standing stocks of four size classes of benthic organisms were compared among three sedimentary provinces in the Venezuela Basin. Total biomass was dominated by microbiota and filter-feeding glass sponges that were abundant in both macrofaunal and megafaunal size classes. The remaingng biomass was divided among predominantly deposit-feeding meiofauna, macrofauna and megafauna. The concentration of biomass in smaller sized classes in the Venezuela Basin was in general agreement with the results of other deep-sea investigations. By contrast, biomass in shallow-water benthic assemblages is concentrated in the larger sized classes. We postulate that these differences in the distribution of biomass among benthic size classes results, in part, from differences in the quality and quantity of organic matter available to shallow-water and deep-sea communities. Most of the labile organic matter that reaches the deep-sea bottom in the Venezuela Basin is consumed at or near the sediment-water interface by surface deposit-feeding and filter-feeding benthos. Transformation of refractory organic matter into utilizable substrate by bacteria in the upper 10–20 cm of sediment provides a source of food for subsurface deposit feeders. Biological mixing may also play a role in the transfer of recently deposited organic matter to subsurface deposit feeders.