RESUMEN
Fast environmental changes and high coastal human pressures and impacts threaten the Mediterranean Sea. Over the last decade, recurrent blooms of the harmful dinoflagellate Ostreopsis cf. ovata have been recorded in many Mediterranean beaches. These microalgae produce toxins that affect marine organisms and human health. Understanding the environmental conditions that influence the appearance and magnitude of O. cf. ovata blooms, as well as how climate change will modify its future distribution and dynamics, is crucial for predicting and managing their effects. This study investigates whether the spatio-temporal distribution of this microalga and the frequency of its blooms could be altered in future climate change scenarios in the Mediterranean Western basin. For the first time, an ecological habitat model (EHM) is forced by physico-chemical climate change simulations at high-resolution, under the strong greenhouse gas emission trajectory (RCP8.5). It allows to characterize how O. cf. ovata may respond to projected conditions and how its distribution could shift over a wide spatial scale, in this plausible future. Before being applied to the EHM, future climate simulations are further refined by using a statistical adaptation method (Cumulative Distribution Function transform) to improve the predictions robustness. Temperature (optimum 23-26 °C), high salinity (>38 psu) and high inorganic nutrient concentrations (nitrate >0.25 mmol N·m-3 and phosphate >0.035 mmol P·m-3) drive O. cf. ovata abundances. High spatial disparities in future abundances are observed. Namely, O. cf. ovata abundances could increase on the Mediterranean coasts of France, Spain and the Adriatic Sea while a decrease is expected in the Tyrrhenian Sea. The bloom period could be extended, starting earlier and continuing later in the year. From a methodological point of view, this study highlights best practices of EHMs in the context of climate change to identify sensitive areas for current and future harmful algal blooms.
Asunto(s)
Cambio Climático , Dinoflagelados , Mar Mediterráneo , Floraciones de Algas Nocivas , Monitoreo del Ambiente , EcosistemaRESUMEN
Blooms of the toxic benthic dinoflagellate Ostreopsis cf. ovata can induce ecological and human health issues in certain temperate areas. In order to prevent these negative effects, long-term monitoring studies of O. cf. ovata blooms have been conducted in several impacted areas to have a comprehensive understanding of bloom dynamics and efficient tools for risk management. O. cf. ovata blooms were monitored every summer (from mid-June to the end of August) on five identified sites in Larvotto beach (Monaco, NW Mediterranean Sea), between 2007 and 2019. This time-series represents one of the largest time-series in the world describing blooms of this species. Bloom phenological features (timing, duration, maximum cell abundance and growth rate), were found to be highly variable throughout the studied period, and were analyzed as a function of different hydroclimatic parameters, including sea surface temperature (SST). The highest net growth rates were related to temperatures ranging between 21°C and 25°C, and did not coincide with maximal temperature records (27.5°C). Such results suggest that, although global warming possibly influences the expansion of O. cf. ovata from tropical to temperate waters, the definite impact of temperature on bloom dynamics might be more complex than a simple facilitation factor for algal growth, at least in NW Mediterranean waters. Furthermore, monthly SST anomalies calculated over this 13-year survey showed a strong positive correlation between spring SST positive anomalies and the bloom starting date, indicating that blooms occurred earlier in the season when spring SSTs were warmer than usual. Overall results provide tools to modelers and managers who are facing crucial challenges to predict the distribution and phenology of O. cf. ovata blooms in European coastal waters, moreover in a context of global warming.