Coral Ultrastructural Response to Elevated pCO2 and Nutrients During Tissue Repair and Regeneration

Corals and coral reefs have recently experienced widespread decline attributed to anthropogenic pressure on reef systems. Studies have demonstrated that nutrient and pCO ₂ stress effect coral growth and calcification, but study of specific effects on coral tissue is lacking. The objective of this research was to examine wound healing in corals and how it is affected by exposure to elevated nutrients and pCO ₂ . Coral tissue repair and regeneration during wound healing in Montastraea cavernosa and Porites astreoides were assessed histologically and ultrastructurally by examining colony fragments exposed to elevated nitrate, phosphate, and pCO ₂ . In M. cavernosa, tissue repair was facilitated by granular amoebocytes, and the zooxanthellae population size increased under enriched nutrient conditions. In P. astreoides , zooxanthellae chloroplasts were markedly abnormal in phosphate-enriched corals, and the concentration of chromophore cells at the healing tissue front was markedly lower under elevated nutrient conditions. The area of wound healed was higher after 14 days under every experimental condition in M. cavernosa compared to P. astreoides . In both species, phosphate enrichment had the most deleterious effect on repair and regeneration.