Meeting Abstract
A functional symbiotic association between cnidarians and photosynthetic dinoflagellates is widespread in shallow-water corals. Photosynthesis reaches up to 98% of energetic requirements in corals from oligotrophic environments; heterotrophy contributes up to 60% of the energy demand in eutrophic or turbid waters. Bermuda and Brazilian reefs illustrate such opposing water physicochemistry concerning nutrient status and light availability. We evaluated symbiont density and chlorophyll a content in 18 coral species from both sites under natural conditions and simulated climate changes (-0.3 pH/+2.5 oC), followed by phylogenetic comparisons. We tested for higher symbiont density and chlorophyll a content in Bermuda corals; higher tolerance to bleaching in the Brazilian ones; and an environmentally driven evolution of coral-dinoflagellate symbiosis. Under natural conditions, symbiont density was greater in Bermuda; chlorophyll a content did not differ between sites. After treatment, mean symbiont density reduced ≈30% in corals from both sites. However, despite that mean chlorophyll a content reduced 10% in the northern corals, the Brazilian species increased it in 90%, meaning up to a 7-fold boost in the amount of chlorophyll a per symbiont. These results reveal strong plasticity in the Brazilian corals, a resilience without phylogenetic effect and potentially driven by the greater water nutrient status, suggesting higher energy budget to the holobiont during bleaching.
