| Congresso Brasileiro de Microbiologia 2023 | Resumo: 667-2 | ||||
Resumo:Coral reefs are diverse ecosystems, primarily structured by scleractinian corals, often engaging in symbiotic relationships with Symbiodiniaceae dinoflagellates. Yet, they face decline due to anthropogenic pressures, both acute (like pollutants) and chronic (such as increased ocean temperature due to climate change), evidenced by species succession, reduced diversity, or sudden coral mortality. A key indicator of this decline is coral bleaching, denoting the disintegration of coral-zooxanthellae symbiosis. This study investigates the changes in the pigment profile of Symbiodinium sp., a zooxanthellae residing in Pocillopora damicornis, under thermal stress, exposure to the pathogen Vibrio coralliilyticus, and the influence of a Beneficial Microorganisms for Corals (BMC) consortium. The experiment was carried out in a controlled environment using HPLC for pigment analysis, supplemented by genetic analysis, and density and cell area measurements of Symbiodinium sp. Distinct pigment profiles were identified across different acclimatization and stress conditions. For example, a shift from artificial to natural light during acclimatization elevated the [(diadinoxanthin + diatoxanthin) / chlorophyll a] ratio, indicating a loss of diversity and an altered dominance of zooxanthellae as per genetic data. Thermal stress, both in isolation and combined with the pathogen, resulted in biomass loss, increased pigment ratios [beta-carotene / chlorophyll a], and augmented presence and concentration of pigments from other taxonomic groups. The BMC consortium effectively minimized these effects, suggesting its protective role for the coral. The study of cellular zooxanthellae area further signified pathogenic action under thermal stress. Diagnostic pigment analysis and size approximation modelling were instrumental in estimating the relative contribution to total chlorophyll a biomass by different microorganisms, including diatoms, dinoflagellates, nanoplankton, green algae, and cyanobacteria. Cyanobacteria were identified as part of the coral's microbiota, while green algae and diatoms, as opportunistic microalgae potentially increasing their biomass in response to coral weakening. Nanoplankton, preferentially occupying the coral's endolithic part, were revealed to have limited influence on living tissue but potential importance in biogeochemical cycles. This research underscores the utility of long-term monitoring and pigment profile study in illuminating the complex coral-microalgae relationship, aiding in the understanding and mitigation of coral reef decline. Palavras-chave: bleaching, zooxanthellae, carotenoids, chlorophylls, HPLC Agência de fomento:CNPq | |||||