Under rapidly changing conditions animals have 3 “choices”: migrate, adapt or die. Ocean temperatures are rising rapidly (a byproduct of climate change) and many animals are struggling to keep up. Coral reef animals are especially at risk, with large-scale coral bleaching events occurring in tropical waters around the globe. Recently, a team of researchers found that some coral reef fish are opting to relocate to cooler waters to call home instead of adapting to the changing conditions. Acclimating is energetically costly, and sometimes results in extremely harmful physical consequences.
A team from the University of Texas at Austin examined blue-green damselfish (Chromis viridis), which are commonly found on coral reefs. The research team exposed the damselfish to temperatures 2-4 degrees Celsius above their normal summer temperatures for a period of 27 weeks. The fish that were exposed to the highest temperatures lost 30% of their body weight and some of them died. When given the choice to stay in higher temperature water or relocate, fish preferentially sought out cooler temperatures. This indicates the given a choice, these fish prefer not to sacrifice critical physiological processes.
Given the current state of rising sea surface temperatures, marine fish will need to adapt or move in order to avoid death. Predictions estimate a sea surface temperature increase of 2 to 4 degrees Celsius by the end of the 21st century. While rising sea surface temperatures are nothing new in Earth’s 4.5 billion years of existence, it is the degree and quickness of increase that is the major issue. For adaptation to be successful it requires time and effectiveness; at this point the amount of time for change is not optimal for marine animals. Researchers will continue examining the ability of animals to adapt, but some will also focus on their ability to relocate under such stress. What if ecosystems were able to move to cooler temperatures toward the poles or to deeper waters? Conditions in these areas are not ideal, so it will surely be interesting to see how animals cope with the rapid rise of ocean temperatures.
Journal reference:
Harbury, A., J.L. Johansen, T.J. Nay, J.F. Steffensen and J.L. Rummer. 2016. Adapt, move or die – how will tropical coral reef fishes cope with ocean warming? Global Change Biology. DOI: 10.1111/gcb.13488.
