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The influence of macroalgae on the proliferation and regulation of the benthic dinoflagellate Ostreopsis cf. ovata blooms

Abstract : Algal blooms can be harmful. The global management and forecasting of benthic harmful algal blooms (BHABs) will be of increasing importance in the years ahead and that is what this study sets out to address. The increase over recent decades, in both frequency and geographical range, of the potentially harmful benthic dinoflagellate Ostreopsis cf. ovata can pose real problems for human health. The French Côte d’Azur, the location for this study, is just one of many Mediterranean areas where harmful algal blooms pose a potential economic threat to a tourist-based economy. A review of the existing literature on Ostreopsis spp. blooms shows a severe lack of information about the ecology of O. cf. ovata in relation to biotic substrates, communities and habitats and thus any possible roles these may play in fostering major Ostreopsis spp. blooms. Through a series of in situ experiments on temperate reefs on the Côte d’Azur over the summers of 2015 and 2016 with follow-up experiments in the laboratory, this study establishes that four distinct macroalgal communities harbour different O. cf. ovata abundances. The results indicated that higher abundances were recorded in sites which were dominated by less complex community structures; Turf and Dicyotales, while sites with Cystoseira spp. communities present did not harbour significant microalgal blooms. These results imply that coastal regions with a dominance of Cystoseira-composed-communities could potentially be less prone to blooms or even inhibit Ostreopsis spp. proliferation. Although, no clear relationship was found between inorganic nutrient concentrations and O. cf. ovata abundances, it was observed that in the bloom onset period, nitrogen compounds were higher than in the rest of the study period (both in 2015 and 2016). Multiple human stressors will continue to impact marine vegetation, understanding these impacts and how they then influence bloom dynamics is imperative for the global management and mitigation of BHABs.
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Daniela Catania. The influence of macroalgae on the proliferation and regulation of the benthic dinoflagellate Ostreopsis cf. ovata blooms. Agricultural sciences. Université Côte d'Azur, 2017. English. ⟨NNT : 2017AZUR4083⟩. ⟨tel-01682210⟩

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