Effects of the toxic dinoflagellate Karlodinium sp. (cultured at different N/P ratios) on micro and mesozooplankton

Abstract

An experimental study was carried out to investigate whether two potential predators such as Oxyrrhis marina (phagotropic 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.