Dichotomy between Regulation of Coral Bacterial Communities and Calcification Physiology under Ocean Acidification Conditions

This study investigates how long-term exposure to ocean acidification (OA) affects the physiological health of three coral species (Pocillopora eydouxi, Porites lobata, and Porites rus). By sampling these corals along a natural pH gradient near a submarine CO2 vent in the Northern Mariana Islands, the researchers aimed to understand two key facets of coral health: the stability of their associated bacterial communities and their ability to regulate the pH of their extracellular calcifying fluid (ECF).

The study reveals a clear dichotomy in how these coral species respond to OA. For Pocillopora eydouxi, the bacterial community destabilized as pH levels dropped, following the Anna Karenina principle where stress leads to increased community variability. However, P. eydouxi maintained its ECF pH, suggesting it prioritized investment in calcification at the expense of its microbiome. Conversely, the Porites species exhibited stabilized bacterial communities, characterized by a significant increase in the abundance of the endosymbiont Endozoicomonas, even as their ECF pH regulation began to decline.

Understanding these divergent responses is crucial for predicting how different coral species will fare in a changing ocean. The findings suggest that corals face energy trade-offs under chronic environmental stress. While some species may sacrifice microbial homeostasis to maintain skeletal growth, others may prioritize symbiotic relationships. Identifying these species-specific strategies helps explain why some corals are more resilient than others and highlights the importance of incorporating both microbial and calcification data to assess coral health.