Bertuccio C., Palombieri D., Giacobbe M.G., Manganaro A., Lanteri G., Marino F.

Dinoflagellates belonging to the (family Ostreopsidaceae) genus Ostreopsis are common members of benthic microalgal communities in both tropical and temperate areas. Several Ostreopsis species produce palytoxin (PLTX) and its analogues, a class of highly potent toxins occurring in nature. The dangerous consequences of natural marine toxins can occur through phenomena of bioaccumulation along the food chain. PLTX targets membrane sodium-potassium pumps (Na+/K+- ATPase) responsible for maintaining ionic gradients. Since the last few years, blooms of Ostreopsis ovata have been occurring in the Mediterranean region with increasing frequency, intensity and distribution causing, sometimes, mortality of benthic organisms and human health problems. In order to improve our knowledge about the effects of O. ovata toxicity, directly on vertebrate marine organisms such as Sparus aurata, Dicentrarchus labrax and Argyrosomus regius, we performed an ecotoxicological screening by using a cultured strain of O. ovata, isolated from Isolabella (Ionian coast of Sicily) during a 2009-2010 study. Toxic effects on target tissues and organs (gills) and the survivability of the organisms exposed to O. ovata cells were investigated, in experimental conditions at two different temperatures (20 and 25° C) and two different cell concentrations (500 mL-1 and 1.000 cells mL-1). The results indicated that the effects of O. ovata on the marine organisms tested in this study depends on the concentration of Ostreopsis living cells used for the experimental contamination, the higher temperature amplifying the fish responses. In all exposed fishes, a mechanical damage to the gills and a consequent death by hypoxia was observed. Haemocyte aggregates surrounding both vegetative and encysted forms of O. ovata were evidenced in histological observations of gills. Epithelial hyperplasia, secondary lamellar fusion and sometimes lamellar necrosis have also been documented.