Nearshore coral health is highly influenced by the influx of anthropogenically sourced nutrients into coastal waterways. Excess dissolved organic carbon (DOC) enrichment can weaken the coral-algal symbiosis, resulting in coral stress and bleaching. Recent studies hypothesized that the proliferation of nitrogen-fixing bacteria (diazotrophs) within the coral holobiont plays a crucial role in the maintenance, or contrastingly, the destabilization of the coral-algal symbiosis. Here, we quantify the effects of DOC enrichment on symbiont density, calcification rates, and algal and microbial diversity in the temperate coral, Oculina arbuscula, by exposing symbiotic and aposymbiotic coral fragments to 0, 5, 10, and 20 ppm concentrations of DOC. In fragments exposed to elevated DOC concentrations, we observed reduced symbiont density and calcification rates, and decreases in microbial diversity and a greater relative abundance of diazotrophs. These findings support the hypothesis that DOC enrichment contributes to coral stress and reiterates the importance of reducing nutrient inputs into coastal waterways to protect coral reef ecosystems.Bachelor of Scienc
