Labile dissolved organic carbon (DOC) is a major pollutant in coastal marine environments affected by anthropogenic impacts. DOC can indirectly impact coral health through the rapid proliferation of pathogenic bacteria, but may also directly affect coral physiology.
A controlled aquarium experiment was conducted at the Centre Scientifique de Monaco to investigate the effects of DOC pollution on the physiology of the tropical reef-building coral Stylophora pistillata.
The results show that excess DOC availability significantly decreased the photosynthetic functioning of the symbionts followed by bleaching (i.e. the loss of symbionts from the host tissue). In contrast, symbiont physiology quickly recovered once the DOC enrichment ceased indicating a reversible shift between autotrophic and heterotrophic metabolism. Interestingly, increased ammonium availability delayed DOC-induced bleaching likely by keeping symbionts in a photosynthetically competent state, which is crucial for symbiosis maintenance and coral survival.
Overall, the present study provides further insights into how coastal pollution can de-stabilize the coral-algal symbiosis and cause coral bleaching. Therefore, reducing coastal pollution and sustaining ecological integrity are critical to strengthen the resilience of coral reefs facing climate change.