Toxicity of benthic dinoflagellates on grazing, behavior and survival of the brine shrimp Artemia salina

Harmful algae may differently affect their primary grazers, causing sub-lethal effects and/or leading to their death. The present study aim to compare the effects of three toxic benthic dinoflagellates on clearance and grazing rates, behavioral changes, and survival of Artemia salina. Feeding assays consisted in 1-h incubations of brine shrimps with the toxic Prorocentrum lima, Gambierdiscus excentricus and Ostreopsis cf. ovata and the non-toxic Tetraselmis sp. Brine shrimps fed unselectively on all toxic and non-toxic algal preys, without significant differences in clearance and ingestion rates. Acute toxicity assays were performed with dinoflagellate cells in two growth phases during 7-h to assess differences in cell toxicity to A. salina. Additionally, exposure to cell-free medium was performed to evaluate its effects on A. salina survival. The behavior of brine shrimps significantly changed during exposure to the toxic dinoflagellates, becoming immobile at the bottom by the end of the trials. Dinoflagellates significantly affected A. salina survival with 100% mortality after 7-h exposure to cells in exponential phase (all treatments) and to P. lima in stationary phase. Mortality rates of brine shrimps exposed to O. cf. ovata and G. excentricus in stationary phase were 91% and 75%, respectively. However, incubations of the brine shrimps with cell-free medium did not affect A. salina survivorship. Significant differences in toxic effects between cell growth phases were only found in the survival rates of A. salina exposed to G. excentricus. Acute exposure to benthic toxic dinoflagellates induced harmful effects on behavior and survival of A. salina. Negative effects related to the toxicity of benthic dinoflagellates are thus expected on their primary grazers making them more vulnerable to predation and vectors of toxins through the marine food webs.