Gelatinous phytoplankton detritus aggregates on the Atlantic deep-sea bed

Abstract

Phytoplankton detritus associated with spring and summer blooms of surface phytoplankton rapidly settles to the deepsea bottom at the Porcupine Seabight, North Atlantic, according to earlier descriptions. However, the causes of this large amount of phytodetrital sedimentation to the deep-sea bed were unknown. Detritus material in samples from the bottom and the water column were collected during the Biotrans IV cruise (July to August 1986) on RV “Meteor” to a site more distant from the shelf break (47°N, 20°W) with depths of about 4 500 m. Deposits most often encountered at the bottom were greenish gelatinous aggregates (ca 1 cm) consisting of amorphous mucous substance enclosing single, dispersed algal cells, skeletal elements of protists, and small faecal pellets. Coccolithiphorids (sometimes with preserved cytoplasm and nuclei) were abundant. The most prominent parts in terms of numbers and volumes within the gelatinous aggregates were round faecal pellets having a diameter of 5 to about 80 μm, and consisting of unidentifiable detrital material, folded membranes, and masses of green chlorophyte cells, 3 μm diam. The faecal pellets were identical to those found inside Phaeodaria (Radiolaria), which were collected at the same time in the water column. It is proposed that the loading of drifting phytoplankton-containing mucus flakes with phaeodarian faecal pellets and the entangling of this mucus with spiny phaeodarian cells are important factors in the formation of fast-sinking gelatinous aggregates.