Ocorrence of dinoflagellate cysts in the sediment close to the Patos Lagoon entrance (RS) with emphasis on potentially harmful species

Abstract

Microalgae can from resting cysts under unfavorable environmental conditions for the vegetative cell, through sexual reproduction. The main functions of the cysts are the ability to survive under unfavorable conditions, allow the dispersion of the population to other areas and genetic recombination through sexual reproduction. Many harmful dinoflagellate species produce cysts during their life cycle, which sink to the bottom during the latest stage of a bloom. In order to detect dinoflagellate cysts, samplings were carried out in muddy sediment, close to the Pats Lagoon entrance, approximately from 32º04’ to 32º30’ S and 52º10’ to 51º49’W on the Southern Brazilian coast. Cysts of the potentially harmful dinoflagellates Alexandrium tamarense (up to 180 cysts.cm-3), Scriosiella trochoidea (up to 117 cysts.cm-3) and Gymnodinium cf. catenatum (up to 25 cysts.cm-3) were detected in the samples. Besides these species, other dinoflagellate cysts frequently detected in low concentrations were Protoperidinium cf. compressum, Protoperidinium cf. oblongum, Protoperidinium cf. claudicans, Protoperidinium cf. pentagonum, Protoperidinium cf. minutum, Polykrikos cf. schwartzii e Gonyaulax verior. Although relatively low cysts concentrations were found in the present work, under optimal growing conditions they could germinate and start microalgae blooms. However, deeper and muddy areas, more favorable to cysts settlement, were not sampled at this time and should be included in the next studies about these cysts in south Brazil.