Emerging benthic HABs in the Mediterranean: exploring the connection between Ostreopsis blooms and human respiratory disorders

Abstract

Ostreopsis blooms have intensively been studied in Sant Andreu de Llavaneres beach (NW Mediterranean Sea) since 2007. These dinoflagellates were present from late spring to autumn, with the highest abundances usually during the summer months. Molecular identification revealed that the bloom was clearly dominated by the Atlantic/Mediterranean O. cf. ovata genotype, although O. cf. siamensis was occasionally present. Epiphytic O. cf. ovata concentrations above 105 cells/g FW were continuously recorded during the hot season, forming brown mucilage that coated the benthic macrophyte community. In the water column, numbers above 105 cells/L were sporadically recorded. Repeatedly, in the summer period, people spending long time (several hours) nearby the beach were affected by respiratory symptoms. In 2009 and 2010, the EBITOX project tested the eventual link between health problems and Ostreopsis outbreaks. High-volume air pump samplers were installed in the beach to characterize the marine aerosol. SEM observations revealed the presence of some marine microalgae (mainly diatoms), although Ostreopsis was not clearly visualized in the aerosol. However, a new validated qPCR assay revealed up to 102 cells of O. cf. ovata per filter during an outbreak in 2010. Palytoxin-like compounds (PLTX) concentrations in the aerosol filters were below the detection limit. In contrast, PLTX ranged between 0.1 and 1.2 pg/cell in the microepiphytic assemblages. The potential implication of bacterial assemblages on the observed toxic outbreaks is also under study. High bacterial abundances and activity coincided with Ostreopsis blooms. Several bacterial strains (e.g. Vibrio) detected by DGGE might contribute to the toxicity of the bloom