Aquatic Sciences Meeting, Albuquerque 2001

SS20 Biological Control of Harmful Algal Blooms: Role of Grazers, Parasites, Viruses and Bacteria

Date: Monday, February 12, 2001, Time: 2:45:00 PM

Location: Cochiti/Taos

Gustafson, Jr., D, E, UMCES Horn Point Laboratory, Cambridge, USA, gustafsn@hpl.umces.edu

Stoecker, D, K, UMCES Horn Point Laboratory, Cambridge, USA, stoecker@hpl.umces.edu

POTENTIAL GRAZING ON PFIESTERIA PISCICIDA BY MICROZOOPLANKTON IN THE POCOMOKE RIVER, MD. USA

The grazing pressure (g /day) of natural assemblages of microzooplankton on cultured non-toxic zoospores (NTZ) was measured in water samples collected from sites of different salinity on the lower Pocomoke River in May and August 2000. NTZ of a non-inducible strain (FDEPMDR23) of P. piscicida were stained with a vital green fluorescent dye, 5-chloromethylfluorescein diacetate (CMFDA), and added to treatments with (< 200 µm) and without (<1.2 µm) the natural microzooplankton assemblage. Grazing coefficient, g, varied from 0 to 8 /day in May and from 0 to 5 /day in August. In 6 of 9 incubations with samples of > 9 psu, g was > 2 /day. In the 6 incubations with < 9 psu samples, g was < 2 /day, and in 3 cases was zero. Potential grazing pressure on NTZ varied with date and site, but in incubations with > 9 psu water, g was usually greater than the maximum potential growth rate of NTZ. Microzooplankton grazing is an important factor that may regulate net growth of Pfiesteria piscicida populations in the plankton.

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Aquatic Sciences Meeting, Albuquerque 2001

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