Influence of Temperature and Nutrients on Coral Community Structure on Lagoonal Reefs in Belize

We surveyed thirteen lagoonal reefs along the Belize Barrier Reef System to assess the influence of both sea surface temperature (SST) and nutrient concentration on coral community structure. A novel metric was developed to identify sites as “Low”, “Moderate”, or “Extreme” based on satellite-derived thermal parameters. Nutrient regime for each site was estimated using chlorophyll-a (chl a) concentration, with Extreme sites having the highest chl a concentrations and Low sites having the lowest. Survey results determined that coral species richness, abundance, diversity, coral density (corals/m²), and percent coral cover were lowest for Extreme sites and did not differ between “Low” and “Moderate” sites. Analysis of dominant life history strategies of extant corals on these lagoonal reefs indicated that Low and Moderate sites contained competitive, generalist, weedy, and stress-tolerant species, whereas “Extreme” sites were dominated by hearty stress-tolerant species, and fast growing weedy species; suggesting that corals utilizing these two life history strategies may be best suited to future ocean conditions. Lack of reef community differences between Low and Moderate site types indicate that nutrient and temperature differences are not significant enough to drive community level coral responses. However, differences between communities at Extreme sites compared to Low and Moderate sites suggest that there is a tipping point at which combined global (temperature) and local (nutrient) stresses cause declines in coral community diversity and structure. Our findings suggest that corals exposed to the stressful environmental conditions at Extreme sites may be most likely to dominate future reefs.