Mangroves and seagrasses as nutrient subsidies for coral reefs in the Red Sea

Tropical seascapes often consist of a mosaic of seagrass, mangrove, and coral reef habitats. These habitats are connected by hydrodynamics and animal movement, with the potential for exchange of organic matter between the habitats. As many corals are found in oligotrophic waters, this transfer of material from primary producers may act as a nutritional subsidy to coral reefs. As mangroves and seagrasses around the world are under threat from coastal development, it is relevant to understand their contributions to coral reef nutrient budgets.

In this study, we explore the magnitude and spatial extent of nutrient subsidies from marine vegetated habitats to coral reefs in a warm, oligotrophic sea. Here, we use stable isotope analysis to investigate the export of nutrients from mangroves and seagrasses to coral reefs in the central Red Sea. By measuring the δ¹³C and δ¹⁵N values of seagrass and mangrove plant material and the tissue of corals, we assess the relative contribution of mangrove- and seagrass-derived carbon and nitrogen to tissues of reef-building corals living at varying distances from this vegetation. Our aim is to understand how corals use exported mangrove and seagrass organic matter, and whether corals closer to these habitats benefit from more nutritional subsidies. Quantification of this exchange provides insight into how seagrasses and mangroves might influence coral reefs at a time when they are under threat from multiple environmental and anthropogenic stressors.