Toxicity of three benthic dinoflagellates isolated from the Gulf of Taranto (northern Ionian Sea)

Harmful Algal Blooms (HABs) due to the abundant proliferation of microalgae have spread worldwide and become a global problem causing enormous economic loss and serious impacts on human health. This algal proliferation can causes negative impacts to other organisms via production of natural toxins. Indeed, HABs are often associated with large-scale marine mortality events and various types of shellfish poisonings. The phenomenon is more frequent than in the past, also in temperate waters, so it is very important not only to survey the presence of potential harmful algae but also to further investigate their toxicity. In this work we report on the occurrence and toxicity of three harmful microalgae (Amphidinium carterae, Coolia cfr. monotis and Ostreopsis cfr. ovata) isolated from the Gulf of Taranto (northern Ionian Sea). Our findings confirmed the association of the three dinoflagellates both in benthic and planktonic assemblages, already observed in other temperate and tropical areas. Amphidinium and Coolia abundances did not reach high values during the sampling period while Ostreopsis abundances were lower than those reported by other authors for the north western Mediterranean Sea and the northern Adriatic Sea, both on macroalgae and in the water column. The toxicity of the three cultured strains was tested by Artemia salina and hemolysis tests as well as by the observation of their effects on the first stages of the sea urchin development. The sea urchin embryonic development in vitro was completely inhibited by the contemporary presence of the three species. But this action could be ascribed to the sole Ostreopsis as the addition of the single species to the sea urchins embryos evidenced no effects in presence of Amphidinium or Coolia cells, and an irregular segmentation in presence of the sole Ostreopsis. In particular, this latter species exerted a cytotoxic effect in a dose-dependent manner with a production of deformed embryos even at very low cell concentration. Besides, we evaluated the effect of each dinoflagellate cell lysate on the sea urchin development. Also in this case Ostreopsis has proved to be the most toxic species. However, the A. salina test evidenced that only Amphidinium and Ostreopsis lysate were able to strongly affect Artemia nauplii vitality. Furthermore, Ostreopsis exerted a very strong hemolytic activity in contrast with that observed with Amphidinium and Coolia lysates which was very low. Our results highlight the importance to monitoring the presence of these dinoflagellates whose effects may also be reflected on the early life stages of marine organisms, especially those species, as the sea urchins, important from both an ecological and economic point of view.