During its annual Coral Reef Monitoring activities the Sint Maarten Nature Foundation has recorded incidents of coral bleaching both inside and outside of the Man of War Shoal Marine Protected Area. The Foundation started it’s monitoring dives on Tuesday and discovered numerous coral colonies showing signs of coral bleaching.
Coral bleaching occurs when coral polyps expel algae that live inside their tissues. Normally, coral polyps live in an endosymbiotic relationship with this algae crucial for the health of the coral and the reef. The algae provides up to 90% of the coral’s energy. Bleached corals continue to live but begin to starve after bleaching. Some corals recover.
Above-average sea water temperatures caused by global warming is the leading cause of coral bleaching. However the Foundation does not rule out increased coastal pollution and the impacts of Hurricane Irma and Maria a year ago as contributing to the bleaching; “We have been recording coral bleaching unfortunately. This has us worried since our corals have already suffered quite a bit because of last year’s hurricanes. The Nature Foundation has a coral bleaching response plan and we will monitor the situation and decide whether or not to put the plan into effect. Coral reefs provide approximately 50 million dollars to our economy, and the continued stress on the ecosystem is giving us some concern,” commented Nature Foundation’s Tadzio Bervoets.
The corals that form the great reef ecosystems of tropical seas depend upon a symbiotic relationship with algae-like single-celled flagellate protozoa called zooxanthellae that live within their tissues and give the coral its coloration. The zooxanthellae provide the coral with nutrients through photosynthesis, a crucial factor in the clear and nutrient-poor tropical waters. In exchange, the coral provide the zooxanthellae with the carbon dioxide and ammonium needed for photosynthesis. Negative environmental conditions thwart the coral’s ability to provide for the zooxanthellae’s needs. To ensure short-term survival, the coral-polyp then expels the zooxanthellae. This leads to a lighter or completely white appearance, hence the term “bleached”. As the zooxanthellae provide up to 90% of the coral’s energy needs through products of photosynthesis, after expelling, the coral may begin to starve.
Coral can survive short-term disturbances, but if the conditions that lead to the expulsion of the zooxanthellae persist, the coral’s chances of survival diminish. In order to recover from bleaching, the zooxanthellae have to re-enter the tissues of the coral polyps and restart photosynthesis to sustain the coral as a whole and the ecosystem that depends on it. If the coral polyps die of starvation after bleaching, they will decay. The hard coral species will then leave behind their calcium carbonate skeletons, which will be taken over by algae, effectively blocking coral re-growth. Eventually, the coral skeletons will erode, causing the reef structure to collapse.