The significance of macroscopic aggregates (marine snow) as sites for heterotrophic bacterial production in the mesopelagic zone of the subtropical Atlantic

Abstract

Macroscopic detrital aggregates (known as marine snow) harbor greatly enriched populations of bacteria and protozoans, suggesting that they may be an important site of heterotrophic activity in the deep sea. We collected flocculent marine snow larger than 3 mm in diameter in the mesopelagic zone of the subtropical Atlantic from the submersible, Johnson-Sea-Link. Although the bacteria inhabiting these aggregates incorporated as much or more [ 3H]-thymidine per bacterium than free-living forms, were up to 2 orders of magnitude more abundant on marine snow than in the surrounding seawater, and were twice as large as unattached bacteria, the marine snow itself was rare, ranging from 0.5 to 4 aggregates m −3. Thus the contribution of bacteria inhabiting flocculent marine snow to total bacterial production in the mesopelagic zone was insignificant, ranging from 0.01 to 0.39% over depths of 130 to 650 m.