Time lags between the deposition and meiobenthic assimilation of phytodetritus

Abstract

The importance of freshly produced phytoplankton detritus in the diet of marine meiobenthos in a soft-bottom community was examined in a 14m3 microcosm. Radiolabelled phytodetritus was continuously produced in the water column from January to June by the addition of ^C-bicarbonate. The specific activity of organic carbon in plankton, sediment and meiobenthos was measured during this time. All meiobenthos reached specific activities higher than that of the sediment; recently produced, labelled detritus was more readily assimilated than older sedimentary carbon. However, the proportion of assimilated carbon that was apparently derived from labelled detritus differed greatly between 2 distinct faunal groups found in the top 5mm of sediment. One group, dominated by harpacticoid copepods, reached specific activities identical to that of the phytoplankton. These fauna thus almost exclusively assimilated labelled detritus, and for harpacticoids there was a lag of less than 2mo between detrital deposition and assimilation. The second group included most other meiobenthic taxa and, by late May, still had remarkably low specific activities -from 10 to 30 Oh of phytoplankton values. It appears that most of the organic carbon in the diet of these fauna had been produced prior to January. I suggest that these 2 meiobenthic groupings were segregated by depth in the surface millimeters and that the low specific activity fauna utilized a large, buried reservoir of older detritus.