Aquatic Sciences Meeting, Albuquerque 2001

PC01 Harmful Algal Blooms

Date: Tuesday, February 13, 2001

Location: Southwest Hall

Tang, K, W, Danish Institute for Fisheries Research, Charlottenlund, Denmark, kta@dfu.min.dk

TROPHIC INTERACTIONS BETWEEN PHAEOCYSTIS AND GRAZERS: CAN THE LACK OF TOP-DOWN CONTROL EXPLAIN THE SUCCESS OF PHAEOCYSTIS IN THE OCEAN?

Massive blooms of Phaeocystis frequently create nuisance in coastal waters. Here I tested the idea that the lack of top-down control may contribute to the success of Phaeocystis in the ocean. The feeding and physiological responses of micrograzers (ciliates) and mesograzers (copepods) to Phaeocystis globosa were studied. The planktonic ciliate Lohmanneilla oviformis fed on Phaeocystis single cells at a low rate, but the resultant growth efficiency was near optimal at 37%. The copepod Acartia tonsa fed on single cells at a rate of less than 20% body C/d, and the resultant growth efficiency was near zero. Although A. tonsa could perceive and attack Phaeocystis colonies, ingestion of the colonies was rare. Nauplii of A. tonsa maintained a survival rate of less than 10% on a Phaeocystis diet, and never reached copepodite stage. Low survival and arrested naupliar development were also observed in another copepod species, Temora longicornis. I suggest that low feeding rates by micro- and mesograzers, plus poor recruitment success by mesograzers feeding on Phaeocystis may reduce the top-down control and allow Phaeocystis bloom to develop.

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Aquatic Sciences Meeting, Albuquerque 2001

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