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Effects of the toxic dinoflagellate Karlodinium sp. (cultured at different N/P ratios) on micro and mesozooplankton
Dolors Vaqué, Jordi Felipe, M. Montserrat Sala, Albert Calbet, Marta Estrada and Miquel Alcaraz

An experimental study was carried out to investigate whether two potential predators such as Oxyrrhis marina (phagotrophic dinoflagellate) and Acartia margalefi (Copepoda: Calanoida) had different responses when feeding on toxic (Karlodinium sp.-strain CSIC1-) or non-toxic (Gymnodinium sp1) dinoflagellates with a similar shape and size. Both prey were cultured at different N/P ratios (balanced N/P = 15, and P-limited N/P > 15) to test whether P-limitation conditions could lead to depressed grazing rates or have other effects on the predators. Both predators ingested the non-toxic Gymnodinium sp1, and low or non-ingestion rates were observed when incubated with Karlodinium sp. The dinoflagellate O. marina did not graze at all on Karlodinium sp. at N/P > 15 and very little at NP = 15, as its net growth rates were always negative when feeding on Karlodinium sp. cultured under P-limitation conditions. A. margalefi had lower ingestion rates when feeding on Karlodinium sp. grown at N/P = 15 than when feeding on Gymnodinium sp1, and did not graze on P-limited Karlodinium sp. Nevertheless, feeding on Karlodinium sp. grown under N/P =15 or N/P > 15 did not have any paralyzing or lethal effect on A. margalefi after 24 h. Finally, a direct effect on the viability of A. margalefi eggs was detected when healthy eggs were incubated for 5 days in the presence of Karlodinium sp. grown under N/P =15 or N/P > 15, producing a decrease in viability of 20% and 60% respectively.

Keywords: micro- and mesozooplankton (Oxyrrhis marina and Acartia margalefi), toxic and non-toxic dinoflagellate (Karlodinium sp., Gymnodinium sp1) grazing rates, P-limitation, predator mortality, Karlodinium sp., egg viability.
Contents of this volume Sci. Mar. 70(1) : 59-65 Back PDF
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