Simpler Marine Life Better Equipped to Survive Climate Change

The simpler a marine organism is structured, the better equipped it is for survival during climate change, according to scientists behind a new meta-study.

Scientists of the Alfred Wegener Institute and Helmholtz Centre for Polar and Marine Research have shown for the first time how the complexity of a life form can limit its ability to adapt to a warming climate.

The study, published in the journal Global Change Biology, found that while simple, unicellular bacteria and archaea are able to live in hot, even oxygen-deficient water, marine creatures like animals and plants cannot. Such complex lifeforms reach their threshold at a water temperature of only 41 degrees Celsius (106 degrees Fahrenheit) - relatively low compared to simple bacteria.

"We now asked ourselves why this is so. Why do bacteria, for example, still grow at temperatures of up to 90 degrees Celsius [194 degrees Fahreneheit,] while animals and plants reach their limits at the latest at a temperature of 41 degrees Celsius," first author Dr. Daniela Storch said in a news release.

The scientists realized that the animals' cardiovascular system is what is holding some of them back. Blood circulation supplies all cells and organs of a living organism with oxygen, but can only do so up to a certain maximum temperature. It is beyond this point that the transport system can no longer perform sufficiently.

"In our study, therefore, we examined the hypothesis that the complexity could be the key that determines the ultimate adaptability of diverse life forms," Storch explained. "That means: the simpler the structure of an organism, the more resistant it should be," to climate change that is.

To test their theory, scientists evaluated over 1,000 studies on the adaptability of marine life, ranging from the simplest archaea lacking a nucleus to the most complex plants and animals. In the end, the results were as predicted, where species complexity was directed correlated with higher temperature tolerance.

And for animal and plant species already surviving at their maximum temperature threshold, this means bad news.

"Today, plants and animals in the warmest marine environments already live at their tolerance limit and will probably not be able to adapt," concluded Prof. Dr. Hans-Otto Pörtner of the Alfred Wegener Institute, who initiated the study. "If warming continues, they will migrate to cooler areas and there are no other tolerant animal and plant species that could repopulate the deserted habitats."