A Three-Year Time Series of Toxic Ostreopsis Blooming In A NW Mediterranean Coastal Site: Preliminary Results

Abstract

Epiphytic dinoflagellates of the genus Ostreopsis have been related to harmful episodes in many Mediterranean coastal areas since 1998: respiratory difficulties, fever, and skin irritations affected people exposed to marine aerosols by recreational activities on the beach. Although this genus is widespread in most of the Mediterranean coasts, harmful events have been recorded only in some localities and periods. One of those sites has been studied for 3 years in a high frequency monitoring (EBITOX project) in order to elucidate the relationship between the microalgal community and their toxicity. 1) Bloom dynamics: the epiphytic Ostreopsis bloom starts in late May-early July, and few weeks later is detected in the water, where it reaches maximum concentrations of 104-105 cells·l-1 in July-August; maximum epiphytic concentrations (above 106 cells·g-1 FW) are detected from mid July to mid November. Between December and April, Ostreopsis is not detected in the water, but low epiphytic concentrations are detected sporadically. 2) Species composition: two Ostreopsis species have been identified to bloom together by a molecular PCR-based assay; Ostreopsis cf. siamensis and O. cf. ovata. 3) Toxicity: the bloom is toxic; palytoxin, analyzed by haemolysis assay and HPLC-FLD is detected in epiphytic samples taken during bloom-period. 4) Resting stages: short-dormancy pellicle and thin-walled cysts were observed in bloom-incubated samples, which germinated even after 6 months. Resting cysts have not been detected during the sampling of macroalgae and sediment during no-bloom season