Together in it

Bleaching and diseases are partners in coral crimes

Published: Sunday 15 November 2009

Brain coral with black band disease an abnormal increase in temperatures around Florida Keys during the summer of 2005 led to Katrinaone of the worst hurricanes in US history. Humans left the coast for shelter further inland. The algae coexisting comfortably with the coral reefs fled the unusually warm waters, too, and 90 per cent of the reefs lost their colour. The algae were their source of food, oxygen and colour.

With time the temperatures decreased, the algae went back home and most of the reefs revived. Yet there were sections that remained bleached. These areas were afflicted by diseases.

Marilyn Brandt and John McManus of National Center for Coral Reef Research at the University of Miami in usa, surveyed colonies in the Florida Keys before, during and after the bleaching of 2005 to establish a link between that and diseases.Till date it was known that at one time only one of the two factors worked to destroy coral reefs.

When a reef loses colour, it stops growing but the tissues remain intact. So if the algae were to return, the reef would recover. If afflicted by diseases, chances of recovery are lost. When pathogens were around, the two worked hand in glove: bleaching made corals vulnerable to diseases and diseases exacerbated the bleaching.

This link depends on the coral and the type of disease though. Montastraea faveolata colonies which bleached more, developed white plague infections. Siderastrea siderea colonies with dark spot disease bleached more extensively than healthy colonies.

Understanding how different stressors interact can explain the mortality pattern after large-scale bleaching events. We can institute control measures that are more specific to the causes, said Brandt. The October issue of Ecology reported the study.

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