Brown trout, the top predator in many European streams, may be able to survive in warmer waters under global warming. Many current predictions about the effects of global warming suggest top predators will be some of the hardest hit as ecosystems suffer around them. However, a new study looking at brown trout, the largest organisms in many freshwater streams, suggests their response to warming is more complex.
A team of researchers, led by Gísli Már Gíslason, Professor in Limnology at the University of Iceland’s Faculty of Life and Environmental Sciences, and Ólafur Patrick Ólafsson, MS student in Biology at the University of Iceland, investigated a series of geothermally-heated streams in Iceland to see how well brown trout coped at higher temperatures. Scientists from Iceland, the United Kingdom, Norway, France, Denmark and South-Africa participated in the study.
They expected trout populations would get smaller as temperatures rose above their normal optimum, but instead found that populations were even bigger at higher stream temperatures. Their results are published recently in the journal Global Change Biology.
The Hengill valley in southern Iceland contains 14 streams of different temperatures, ranging from 4-25 degrees C. By tagging trout in a range of streams and measuring them five months later, the team were able to map the growth rate of the populations in each stream. They found that the size of trout populations increased with stream temperature, suggesting they could adapt to warmer climates.
The team investigated how the trout were able to adapt, and found that they benefitted from more efficient energy transfer in the food web – more sunshine creating more algae to feed more prey for the trout – but also from eating less ‘junk food’. However, the scientists emphasize that the brown trout has had a long period to adapt to warmer environments, while predators facing a sudden increase in temperature due to climate change may fare worse.
Trout that live in colder streams use less energy to catch prey, relying on what floats by, but in warmer streams they are more selective, picking out the most energy-intensive food. The study suggests that adult trout can grow and thrive at higher stream temperatures, but they still need cooler waters in order to raise their eggs, which die in waters above 16 degrees C.
The team are expanding their study by looking at similar geothermal systems in Greenland, Alaska, Russia and Svalbard to see if the same pattern of adaptation is repeated across the Arctic region.
(Source: Imperial College London)