Benthic community response to experimental additions of the polychaete Nereis virens

Abstract

Previous field manipulations with the predatory polychaete Nereis virens have indicated the existence of a 3-level interactive system within the infauna in Maine, USA (N. virens — Corophium volutator — other infauna). The purpose of this investigation, carried out in 1980, was to test the hypothesis that the addition of N. virens to a community where the intermediate predator/disturber C. volutator is absent should cause infaunal densities to decrease. Experimental results did not support this hypothesis. In N. virens addition treatments there was a sharp increase in the density of the infauna. Three taxa which accounted for 95% of the individuals in controls (tubificid oligochaetes, Streblospio benedicti, Capitella capitata) were also most abundant in addition treatments. Their rank orders and relative proportions were the same in addition treatments and controls; there was no evidence of a differential response to the addition of N. virens. Mechanisms which explain the rise in infaunal desnity include: reduction of an intermediate predator by N. virens (in this case Nephtys incisa); nutrient enrichment from N. virens fecal material; and sediment modification caused by N. virens burrowing and surface activities. The explanation most consistent with the data is the intermediate predator hypothesis. The results of this and other experiments suggest the importance of complex trophic interactions within the infauna.