As Corals Bleach, Fish Species Lose Camouflage, Pushing Predation Losses Higher - Nature

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Fish that usually camouflage themselves among colourful coral reefs are losing their ability to hide from predators as corals are bleached by Earth's acidifying oceans.

Bleaching often leads to coral death, and is a stress response to two key factors: increasing ocean acidity, caused by uptake of carbon dioxide from the atmosphere, and a rise in ocean temperature. It's all too apparent that ecosystems near bleached corals tend to collapse, but the reasons why are not fully understood.

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The team filled aquaria with Pocillopora damicornis corals and added two species of damselfish (Pomacentrus moluccensis and Dascyllus aruanus) that like to hide around them. The corals were either healthy, bleached, recently dead from bleaching or long-dead and covered with thick green algae. After the damselfish had spent an hour acclimatizing to their surroundings, a predatory reef fish, the dottyback (Pseudochromis fuscus), was introduced into each aquarium for 75 hours.

The team report in the journal Behavioral Ecology1 that predation rates — the proportion of damselfish taken by the dottybacks — were 33% on bleached corals, 37% on recently dead corals and 42% on dead corals covered in algae. These figures contrast sharply with the 25% predation rate that took place in aquaria with healthy corals. Coker and his colleagues believe that the increase in predation is linked to both the loss of camouflage and of hiding space for the damselfish. The initial bleaching probably makes the brightly coloured fish easier for the predators to see, explains Coker, so fish populations begin to suffer even before the coral is dead.

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http://www.nature.com/news/2009/091021/full/news.2009.1023.html