Excessive nutrients from land can cause coral bleaching: Study

A recent study has identified new causes for coral bleaching, namely excessive nutrients from fertilisers and storm-water runoff.

Coral reefs are among the most diverse ecosystems in the world. They provide shelter and nourishment to fish and other marine organisms. Vibrant and healthy reefs form when a coral and an algae — zooxanthellae — start a symbiotic relationship.

The coral provides protection and compounds zooxanthellae’s need for photosynthesis. The algae produces carbohydrates and helps remove the coral’s waste.

But when the corals are stressed due to change in temperature, light and nutrients, they expel the algae and turn white. Corals will die if such bleaching extends.

The ARC Centre of Excellence for Coral Reef Studies in Australia, examined skeletal cores of long-living corals in the Red Sea. The Red Sea was chosen as a study area because it is one of the only marine environments where the effects of summertime nutrients and heat stress are independent of each other.

Corals bleach only when high sea surface temperatures couple with high nutrient levels. Nutrient stress on corals is difficult to measure though. Hence, only temperature-based stress was considered to predict coral bleaching.

Incorporating nutrient-supplying ocean currents into coral bleaching forecasts can enhance the predictions, the researchers said.

According to the National Oceanic and Atmospheric Administration(NOAA), the US lost half of its coral reefs in the Caribbean in one year (2005) due to a massive bleaching event. 

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