Coral reef ecological pump for gathering and retaining nutrients and exporting carbon: a review and perspectives

Abstract

How coral reefs with high productivity and biodiversity can flourish in oligotrophic tropical oceans has inspired substantial research on coral reef ecosystems. Increasing evidence shows that similar to water in an oasis in the desert, there are stable nutrient supplies to coral reefs in oligotrophic oceans. Here, with emphasis on the fluxes of organic matter, we summarize at the ecosystem level (1) the multiple input pathways of external nutrients, (2) the storage of nutrients in reef organisms, (3) the efficient retaining and recycling of dissolved and particulate organic matter within coral reef ecosystems, (4) the distinctly high phytoplankton productivity and biomass inside and near oceanic coral reefs, and (5) the export of reef-related organic carbon to adjacent open oceans. These properties enable coral reefs to function as ecological “pumps” for gathering nutrients across ecosystems and space, retaining and recycling nutrients within the ecosystem, supporting high phytoplankton productivity, and exporting organic carbon to adjacent open oceans. Particularly, the high phytoplankton productivity and biomass make waters around coral reefs potential hotspots of carbon export to ocean depths via the biological pump. We demonstrate that organic carbon influx is vital for coral reef ecosystems’ carbon budget and carbon export. The concept of the coral reef ecological pump provides a framework to improve the understanding of the functioning of the coral reef ecosystem and its responses to disturbance. Prospects of the coral reef ecological pump in coral reef studies are discussed in changing oceans driven by human activities and global change in the Anthropocene.