Coral bleaching makes fish behave recklessly

Sonali Deshpande
Mr. Mathieu
March 10, 2014
Author: Sandhya Sekar
Published: Feb 14, 2014
Article URL: http://www.newscientist.com/article/dn25059-coral-bleaching-makes-fish-behave-recklessly.html#.Ux5GL_ldWSo

Summary
     Oona Lonnstedt of the Australian Research Council's centre for coral reef studies and her colleagues conducted a study on how the fish known as pallid damselfish behave in the Great Barrier Reef. They were looking to find the difference between the behaviors of the fish that lived in and around live coral versus the fish who lived in dead coral, as coral bleaching is an event that often leaves coral dead. The result was that the death rate of the fish on the dead coral was 75% higher than those on the live coral. They observed that fish on the dead coral seemed to take more risks and branch out, while, unlike those on the live coral, not smelling the injury of a mate. If a fish smelled the injury, they would take cover, which they did in the live coral. Because the fish on the dead coral did not take cover, Lonnstedt suggested that dead coral masks chemical signals, so that the fish would swim farther out to find them. It was agreed, however, that if the rate of coral mortality increases, the diversity of fish will decrease.

Connection
     This article relates to our microbes unit, where we first learned about coral bleaching. Coral often forms a mutualistic relationship with unicellular zooxanthallae algae, which lives in their tissues. The coral polyps provide the algae with a structure to live on, so that they can be closer to the sunlight, and have shelter and protection. Also, the algae provides its products of photosynthesis to the coral in exchange for inorganic materials. When conditions get extreme, such as a temperature increase, the coral expels the algae, making the coral a white color. From bleaching, corals often die.