Ostreopsis

Mass appearances of the toxic dinoflagellate genus Ostreopsis are known to cause dangerous respiratory symptoms in humans exposed to aerosols. The outbreaks can appear in shallow marine waters of temperate regions around the globe. We followed a massive bloom event on a public beach on the northern Adriatic coast near Rovinj, Croatia. We identified the responsible species and the produced toxins as well as the
dynamics of the event with respect to environmental conditions. Ostreopsis cf. ovata appeared in masses from September through October 2010 on a public beach near Rovinj, Croatia but stayed undetected by public health organizations. Respiratory symptoms were observed whenever humans were exposed to substrate samples containing large numbers of Ostreopsis cells. During the mass abundance of O. cf. ovata also exposure to the aerosols on the beach evoked respiratory symptoms in humans. Our measurements showed high cell abundances and high toxin contents with a stable relative contribution of putative Palytoxin and Ovatoxins a-e. Artificial beach structures proved to dramatically reduce settling of the observed Ostreopsis biofilm. Blooms like those reported herein have a high potential to happen undetected with a high potential of affecting the health of coastal human populations. Increased monitoring efforts are therefore required to understand the ecology and toxicology of those bloom events and reduce their negative impact on coastal populations.

Blooms of the toxic dinoflagellate Ostreopsis genus are a recurrent phenomenon in tropical and temperate regions worldwide. The most widely distributed species in the Mediterranean Sea, Ostreopsis cf. ovata, produces blooms with increasing intensity, frequency and distribution. These blooms have been associated with respiratory problems and skin irritations in humans, causing health problems along Italian coasts. In addition, palytoxin-like substances produced by this species can be accumulated by various organisms and make the seafood toxic, with further risks to human health. This thesis is based on the analysis of a multiannual dataset gathered at different coastal sites along the Campania region: 1) the area of Posillipo, in the Gulf of Naples, where the most intense blooms of O. cf. ovata for the Campania Region are regularly recorded; 2) the Ischia Island coasts, which are subjected to natural acidification due to the presence of volcanic vents; 3) the sandy littoral of the Gulf of Salerno littoral, where O. cf. ovata has not been found previously, and where structures for the defence from coastal erosion will be built. Results showed that: i) Ostreopsis cf. ovata blooms are a stable phenomenon, occurring at regular frequency over the years in summer months along Posillipo and Ischia Island coasts; ii) the blooms show a marked seasonality, with peaks in the summer months, thus representing a risk for people during the bathing season, either through direct contact and aerosol or following the consumption of contaminated seafood; iii) based on the results from the Ischia island, a lower pH does not affect Ostreopsis blooms, meaning no risk decrease in future scenarios of ocean acidification; iv) Ostreopsis does occur in the Gulf of Salerno, although at low concentrations, probably due to the absence of a suitable substrate; by providing a hard substrate for macroalgae hosting Ostreopsis blooms, artificial structures against coastal erosion might determine an increase of the species in an area where it has not represented a risk so far. The present study highlights the relevance of appropriate strategies for monitoring Ostreopsis blooms. Knowledge and data obtained can be used for a better assessment and interpretation of these phenomena, thus supporting informed management actions to protect the environment, seafood resources and human health.