Grazing of the free-living filamentous brown seaweed,Pilayella littoralis, by the amphipodGammarus tigrinis

Abstract

AbstractPilayella littoralisis a common brown alga with a cosmopolitan distribution. A distinct form of the alga is found free-living in Nahant Bay, Massachusetts. Characteristics that distinguish the free-living form include radial branching that results in a ball-like morphology, reproduction by fragmentation of filaments rather than by spores, and year-round persistence of the population. The amphipodGammarus tigrinisis frequently found within the floating drifts ofP. littoralis. We conducted gut content analyses to document thatG. tigrinisconsumesP. littoralis. Culture studies revealed that ingestedP. littoraliscould survive and grow from fecal pellets produced byG. tigrinis. In addition, inefficient grazing produces vegetative fragments (propagules) that can increase numbers within the free-living population. δ13C values for the amphipods andP. littoralisaveraged -17.4 o/oo and -17.7 o/oo, respectively, suggesting thatG. tigrinisacquires most of its carbon fromP. littoralis.