AME 28:79-85 (2002)  -  doi:10.3354/ame028079

ABSTRACT: Susceptibility of actively toxic (TOX-A) zoospores, temporarily non-toxic (TOX-B) zoospores, and zoospores non-inducible to toxicity (NON-IND) of Pfiesteria piscicida to microzooplankton grazing was compared in a laboratory experiment. Zoospores from all cultures were ingested by microzooplankton, but community grazing coefficients for TOX-A were <20% of those for TOX-B or NON-IND zoospores in 6 h incubations. Tintinnids and strobilidiid ciliates that fed on P. piscicida declined in incubations containing TOX-A zoospores. There was no decline in a strombidiid ciliate or heterotrophic dinoflagellate populations that fed on TOX-A zoospores. These data suggest that, although microzooplankton grazing on non-toxic zoospores can be a significant source of mortality to planktonic populations of P. piscicida, grazing on toxic or very recently toxic zoospores is relatively low.

KEY WORDS: Pfiesteria piscicida · Zoospores · Toxicity · Microzooplankton · Grazing