Algae on the reef

Image: A hard brain coral grows only 1-3 cms a year, if it is covered in algae though this growth rate can slow to zero. 


Throughout our three survey dives today we saw reefs covered in excess amounts of algae. Algae resides right at the bottom of the oceanic food chain and is a necessary organism on a healthy reef. However given the right conditions algae can grow very quickly and overwhelm hard corals which are the building engineers of tropical reefs. Named for their calcium carbonate ‘hard’ skeleton, hard corals, such as brain corals and boulder corals, grow very slowly, only around one to three centimetres each year. If they are smothered by algae, it is difficult for hard corals to grow at all. Also, as algae spreads over the reef, new coral juveniles can’t settle onto a coral surface, preventing the growth of new corals and expansion of the reef.

A solution - bring back the fish.

Algae are found in water with lots of nutrients, often close to the coast. On coral reefs, grazing herbivorous fish (such as parrotfish and surgeonfish) eat a lot of algae, keeping it in check, but many of these fish have been caught in Belizean waters. In April 2009, the Belizean authorities legislated full protection to these ‘cleaners of the reef’. Since then, there are reports that the amount of herbivorous fish in the area is increasing. (Healthy Reefs 2012 Report Card for the Mesoamerican Reef). We have seen abundant fish life on the reefs around Belize so hopefully, in time, we will see less algae in the area.