Researchers in the United Kingdom have published a study that says an imbalance in nutrients in waters where coral reefs are located can increase coral bleaching. The University of Southhampton study, published in the journal Nature Climate Change states that corals and zooxanthellae, an algae that lives in coral polyps and which the corals are dependent for survival can suffer when high water temperatures block photosynthesis in the zooxanthellae, which can cause a buildup of oxygen compounds that are toxic to corals. The toxic compounds can lead to an algae die off, which in turn causes the corals to bleach, or turn white. When bleaching occurs, it often kills the corals.
In their study, the researchers say that when dissolved nitrogen compounds increase and the availability of phosphate decreases, this results in phosphate starvation of the algae. This in turn reduces the ability of the algae to photosynthesize, which exposes the coral to temperature and light-induced bleaching.
“Our findings suggest that the most severe impact on coral health might actually not arise from the over-enrichment with one group of nutrients, for example, nitrogen, but from the resulting relative depletion of other types such as phosphate that is caused by the increased demand of the growing zooxanthellae populations,” said Dr. Jörg Wiedenmann, senior lecturer of Biological Oceanography at the University of Southampton and head of the Coral Reef Laboratory, who led the study.
“Our results have strong implications for coastal management. The findings suggest that a balanced reduction of the nutrient input in coastal waters could help to mitigate the effects of increasing seawater temperatures on coral reefs. However, such measures will be effective only for a short period of time, so it is important to stop the warming of the oceans, which will otherwise destroy most of the reefs in their present form in the near future.”