Bacteria and cyanobacteria associated with phytodetritus in the deep sea

Abstract

Sedimentation of phytodetrital aggregates from euphotic waters to the deep sea has been recognized in recent years as probably the most important source of energy for the deep-sea ecosystem^1–3. Little is known, however, of the processes by which the detritus is degraded. We report here on phytodetrital aggregates collected from the sediment surface 4,500 m deep in a mid-oceanic area of the northeastern Atlantic. The aggregates contained a rich community of active bacteria and cyanobacteria. The abundance of intact cyanobacteria indicates that the phytodetritus is sedimented rapidly and that picoplankton, which form a significant fraction of primary production during summer months, can be transported from surface waters to the deep sea by attachment to aggregates. Rapid bacterial growth occurred on the detrital material when incubated under deep-sea conditions and similar growth rates were found under surface-water incubation conditions. The results show that phytodetritus is rapidly used by deep-sea adapted bacterial populations and that the biological degradation and transformation of sedimented detrital material in the deep sea is faster than hitherto assumed.