ABSTRACT: Ultraplankton, heterotrophic and autotrophic plankton <5 µm, are the most abundant food source in the world's oceans, yet their role as a food source for macroinvertebrates is largely unexamined. We quantified in situ feeding on heterotrophic and autotrophic plankton <10 µm by the boreal sponge Mycale lingua using measurements that quantified sponge feeding efficiencies, pumping rates, and abundance to determine the contribution of plankton <10 µm to sponge carbon intake. Using dual-beam flow cytometry we identified 5 populations of plankton <10 µm: heterotrophic bacteria, Prochlorococcus, Synechococcus-type cyanobacteria, autotrophic eucaryotes <3 µm, and autotrophic eucaryotes 3 to 10 µm. Mycale lingua nonselectively grazed on all types of plankton <10 µm. Prochlorococcus was filtered with the highest efficiency (93%), followed by Synechococcus-type cyanobacteria (89%), autotrophic eucaryotes 3 to 10 µm (86%), heterotrophic bacteria (74%), and autotrophic eucaryotes <3 µm (72%). We conservatively estimate that M. lingua at naturally occurring densities can obtain 29 mg C d^-1 m^-2 feeding on plankton <10 µm, with 74% resulting from ultraplankton, suggesting that ultraplankton are an important overlooked component of benthic-pelagic coupling.

KEY WORDS: Ultraplankton · Sponges · Suspension feeding · Benthic-pelagic coupling · Mycale lingua · Gulf of Maine

Published in MEPS Vol. 141 (1996) on October 3
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 1996