Nutrient and sediment loading affect multiple facets of functionality in a tropical branching coral

Area of Science:

• Marine Biology
• Ecology
• Coral Reef Science

Background:

• Coral reefs are vital ecosystems threatened by anthropogenic stressors like warming, sedimentation, and nutrient loading.
• A comprehensive understanding of how these stressors impact coral functionality is essential for effective conservation.

Purpose of the Study:

• To investigate the effects of a natural nutrient and sedimentation gradient on coral functionality in Mo'orea, French Polynesia.
• To quantify the relationship between metabolic rates and temperature using thermal performance curves along this gradient.

Main Methods:

• Measured endosymbiont and coral host responses, holobiont metabolism, and coral cover of *Pocillopora acuta*.
• Utilized thermal performance curves to assess metabolic responses to temperature variations.
• Analyzed nutrient and sediment impacts across a natural environmental gradient.

Main Results:

• Increased nutrient input led to higher endosymbiont density and chlorophyll *a*, but lower nitrogen content per cell.
• Nutrient and sediment loading reduced coral metabolic performance under thermal stress, decreasing respiration, photosynthesis, and calcification rates.
• *Pocillopora acuta* colony cover declined significantly along the nutrient gradient.

Conclusions:

• Nutrient and sediment pollution negatively affect multiple coral functions, from symbiont dynamics to overall colony health.
• Local stressors impair coral's ability to cope with thermal stress, highlighting the need for managing land-based inputs.
• Findings provide critical insights for coral reef management, emphasizing the mitigation of coastal pollution.