The influence of urban pressures on coral physiology on marginal coral reefs of the Mexican Pacific

Coral ecosystems in the central Mexican Pacific inhabit environmental conditions considered as suboptimal for reef development, such as wide ranges in temperature, low pH, and cyclonic activity. In addition, they are facing increasing nutrient and sediment inputs as a consequence of urban growth and tourism. While the global effects of anthropogenic stressors to coral communities have been described, the local response and microscale variations remain unknown. Therefore, the present study evaluates three physiological markers during 2018 (total lipid content, symbiont density, and chlorophyll a concentration) in the main reef-building coral genera ( Pocillopora , Porites , and Pavona ) from two coral communities: one coastal site next to a luxury touristic development with high sedimentation rates and elevated nutrient inputs from golf courses, and one at an insular MPA 6 km distant from the coast and where human activities are regulated. At each coral sampling site, nitrite, nitrate, and phosphate concentrations as well as sedimentation rates were measured. The analyses of the physiological markers showed significant differences in the lipid content and symbiont density between sites, with corals at Isla Larga presenting higher lipid content but lower symbiont density, while pigment concentration only differed across months. When assessing differences among coral genera, Pocillopora colonies presented the highest lipid content, while Pavona showed more symbionts and Porites colonies the uppermost pigment concentrations, with significant differences among genera and across the studied months. Environmental characterization showed significant differences between sites in the nitrate concentration and sedimentation rates. Generalized nonlinear models evidence that lipid concentration is related to sedimentation rates and temperatures, symbiont density to nitrite and phosphate concentrations, and pigment concentrations to nitrate and phosphate concentrations as well as sedimentation rates.