We know that acidic conditions can cause damage to sensitive corals on our reefs but a recent study on clownfish has shown that increased acidity in water can cause them to lose their hearing. The study used sounds of predators to see if the clownfish responded the same in water with a higher acidity than in normal seawater finding that at levels of acidity that may be common by the end of the century, the fish did not respond to the sounds of predators.
As oceans face increaced acidity from absorption of CO2 from the atmosphere, the higher acidity and loss of hearing can put the survival of fish in danger notes the scientific team that conducted the study published in the journal Biology Letter.
“Avoiding coral reefs during the day is very typical behaviour of fish in open water,” said research leader Steve Simpson from the School of Biological Sciences at the UK’s Bristol University. “They do this by monitoring the sounds of animals on the reef, most of which are predators to something just a centimetre in length. But sounds are also important for mate detection, pack hunting, foraging – so if any or all of those capacities are gone, you’d have a very lost fish..”
Earlier research has shown that fish also tend to lose their ability to scent danger in slightly more acidic seawater and now two major senses and modes of defense are being nullified by rising acidity in oceans.
The team raised baby clownfish in tanks containing water at different levels of acidity with one tank mimicking the seawater of today, with the atmosphere containing about 390 parts per million (ppm) of carbon dioxide. The The other tanks were set at levels that could be reached later this century — 600, 700 and 900 ppm. An increase in atmospheric CO2 means the more CO2 is absorbed by the seas and in turn, increasing the acidity of the water.
The team used an underwater speaker that played sounds of predators recorded in their natural habitat to see if the fish would swim towards or away from the sounds. In the tank with acid levels of today’s oceans, 75% of the time the clownfish fled to the other side of the aquarium away from the loudspeaker.
At higher levels of CO2, the fish showed no preference suggesting to the team that they cannot hear or decipher the noises as a potential danger.
“The reef has been described as ‘a wall of mouths’ waiting to receive the clownfish,” said Dr Simpson. “What we have done here is put today’s fish in tomorrow’s environment, and the effects are potentially devastating.”
The team postulates that if it takes several decades for the oceans to reach these more acidic levels, there is a chance that fish could adapt also if other species of fish will be similarly affected. A major question the teams hopes to answer is why these fish are affected by increased acid levels.
With no apparent physical damage to their ears the team suggests there could be some effect on nerves, or maybe they are stressed by the higher acidity and do not behave as they otherwise would. As increased awareness over increased levels of CO2 in the atmosphere and global warming, we are seeing more and more data showing this increase in acidity and temperature causing havoc with the delicate reef ecosystem.
Thanks to Jonathan Dooley for the heads up!
[via BBC, image courtesy of “Nemo’s great uncle” on Flickr]
