Heat could kill off fish

Fish that live in the Mediterranean are in danger of being killed off, according to a Greek study seen by Kathimerini which shows that rising sea temperatures could have a devastating effect on sea life. Research released yesterday by the Aristotle University in Thessaloniki suggests that a rise of just a few degrees in the temperature of the sea will cause fish to die in vast numbers. The study was made public on the same day that climate scientists in Britain predicted that 2007 will probably be the hottest year on record. Greek researchers have been conducting tests for the last five years to establish the impact that a rise in sea temperatures and an increase in the amount of carbon dioxide in the water will have on sea organisms. «We are researching the lowest temperature above which the effect on fish will be seen,» the head of the program, Assistant Professor Vassilis Michailidis, told Kathimerini. «It is especially important that the tolerance levels of the organism to changes in their environment be established.» Earth’s average temperature has increased by up to 1 degree Celsius over the last few years and scientists predict that it will increase by some 5 degrees Celsius over the next few decades. The university’s research indicates this could kill off fish in Greek seas. «The fish in the Mediterranean, especially the sea bream that we have studied – as they are the most popular type in fish farms – ideally live in temperatures of 18-22C,» said Michailidis. «Above 26C, fish cannot breath well and do not take in enough oxygen,» he added. «When the temperature rises above 29C their cardiac system does not operate well and there is an increased rate of death.» Scientists have also identified the increasing amount of carbon dioxide in seawater, which makes it more acidic, as a threat to fish. «The constant emissions of carbon dioxide will lead to a fall in the pH value of seawater from 8.2 to 7.4 over the next 90 year,» said Michailidis. «Experiments have shown that organisms should not be exposed to these pH levels.» Even if fish such as the sea bream, which is common in Greek waters, survive these changes, scientists believe that many other organisms on which fish feed will be killed, thereby putting fish at risk as well.