Distribuição espacial, em microescala, e sazonal das microalgas potencialmente toxígenas Dinophysis spp. (Ehremberg 1839) na ilha Guaíba (Mangaratiba, RJ) e suas possíveis implicações no cultivo de moluscos bivalvos

Abstract

At Guaiba island (Mangaratiba municipality, south coast of Rio de Janeiro) is located the Association of Marine Maricultores of Mangaratiba s farm. The region has excellent conditions for growth of molluscs bivalves: mild water temperatures, mesotrophic and with good sanitary conditions (under bacteriological aspects). The crop is the main shellfish mussel Perna perna, which feeds mainly phytoplanktonic organisms (microalgae). However, the phytoplankton community may be present harmful microalgae such as dinoflagellates Dinophysis spp. that can produce diarrhoetic toxins. The main diarrhoetic phycotoxin produced by these microalgae is okadaic acid (OA), previously detected in the region and associated with D. acuminata. This phycotoxin is implicated in the syndrome Diarrhoetic Shellfish Poisoning, which affects humans, showing the acute effect gastrointestinal symptoms (vomiting, abdominal pain and diarrhea) and chronic promotion of carcinogenesis in the stomach and intestine. Regarding the animal sanity OA affects the immune system of mussels making them susceptible to pathogens and pollutants. In addition is genotoxic and can lead to loss of genetic biodiversity of P. perna. This effect can generate mutations that compromise the future generations of shellfish can lead to disastrous consequences for the mitiliculture. Dinophysis as planktonic organism, has a limited ability to swim. However, under conditions of stability of the water column the dinoflagellate may attach to certain depths, which may become an aggravating factor in the contamination of shellfish if production of OA. This distribution on the microscale is from the interaction between biotic and abiotic factors. Thus the present work to identify and quantify the Dinophysis species present at Guaiba island and verify whether the formation of density along the water column over a year. Were collected monthly, in high tide, over a vertical profile of 8 meters deep. The microalgae were collected with Van-Dorn bottle and fixed with formaldeído for further work on microscopy. We measured temperature, salinity, Secchi depth. Climatological data of rainfall, intensity and direction of winds were released by Vale. We identified 6 species of Dinophysis: D. acuminata, D. caudata, D. fortii, D. ovum, D. tripos and D. rotundata. The Cluster analysis revealed D. acuminata was dominant (Fitopac v1.6, p <0001), besides being the most frequent and abundant throughout the year. Only the species during summer showed higher cell density (average of 297 células.l-1, a low relative abundance according literature) in the stratum of 0-4 meters deep, than in the stratum > 4 meters (160 células.l-1), significantly different from the rest of the year (ANOVA, p <0.0001). D. fortii and D. rotundata were codominant in summer and autumn/winter, respectively. The remaining species occurred as incidental. D. ovum only occurred in summer and this work is the first report of this species in Brazilian waters. Redundancy analysis showed that the hydrological and climatological parameters analyzed only salinity and wind (selected by the Monte Carlo test) explained 11% of the variance of the data distribution of Dinophysis. Although no analysis has been performed for the presence of okadaic acid that all identified species are reported as potential producers of toxins diarrhea. Thus it is necessary for an evaluation of risk for diarrhoetic toxins aimed at animal health and safety to public health in the region.