Warming Ocean Forces Coral Reef Fish to Relocate to Cooler Waters

A new study revealed that the rapid warming of oceans are forcing coral reef fishes that are not capable of adapting to the increasing temperatures to relocate to the cooler parts of the ocean, sometimes ending up in a areas with less than ideal living conditions.

The study, published in the journal Global Change Biology, highlighted the fish's ability to adapt to the increasing temperature and move to the cooler parts of the ocean the mitigate the negative effects of warmer waters.

"When given the slightest chance, fish can seek out temperatures that they've evolved to be in over thousands of years, to mitigate the impact of increasing temperatures and not sacrifice critical physiological processes," explained lead author Adam Habary of the University of Copenhagen, in a press release.

For the study, the researchers conducted experiments on the common coral reef fish blue-green damselfish. The fish was acclimated to two to four degrees Celsius above their normal summer temperature over a 27-week period.

The researchers observed that the fish, if given a choice to stay in a habitat reflecting their acclimation temperatures or relocate, chose to move to cooler waters. Additionally, fishes that need to deal with higher temperatures needs more energy to cope and may not handle the stress, reproduce or grow. The researchers also noted that some of the fish acclimated to the highest temperatures loses about 30 percent of their body weight and some even died.

Their findings might provide mechanistic explanation for the polar migration of many coral reef fish and pelagic fish such as tuna. However, researchers noted that there some coral reef fish that are highly dependent on reefs for habitat. Due to the this, corals and coral reef fish will have to adapt or move to deeper waters where living conditions are less than ideal.

Furthermore, the researchers observed that the steady increase of temperatures is not the one causing the most damage. The ocean warming that often occurs as severe and increasingly frequent events are responsible for the most of the damages in marine ecosystem. As an example, the researchers cited the widespread coral bleaching in the Great Barrier Reef earlier this year, when temperatures rose as much as four degrees Celsius for several weeks.