A team of scientists from the University of Adelaide discovered that when fishes interact in groups, they are exhibiting signs of distress caused by ocean acidification and global warming.
Fish show gregarious behavior and cluster in shoals which helps them to acquire food and for protection against predators. Many gregarious tropical species are shifting poleward under current ocean warming and interacting in new ways with fish in more temperate areas.
Ivan Nagelkerken, Professor and Project Leader, Environment Institute and Southern Seas Ecology Laboratories, University of Adelaide
The scientists conducted controlled laboratory experiments to study how species interacted and behaved under changing temperatures and acidification conditions.
Ocean acidification and an increase in ocean surface temperatures are caused by rising atmospheric carbon dioxide concentrations. While warming and acidification are two different phenomena, their interaction negatively affects marine ecosystems.
We found that tropical and temperate fish species tend to move to the right when coordinating together in a shoal especially when spooked by a predator, but this bias significantly diminished under ocean acidification.
Angus Mitchell, PhD Student, University of Adelaide
Mitchell carried out the experiments as part of this study.
“Mixed shoals of tropical and temperate species became less cohesive under future climate conditions and showed slower escape responses from potential threats,” added Professor Nagelkerken.
Professor David Booth from the University of Technology, Sydney also contributed to the study.
Our findings highlight the direct effect of climate stressors on fish behavior and the interplay with the indirect effects of new species interactions.
David Booth, Professor, University of Technology
The researchers published the results of the study in the journal Global Change Biology.
“Strong shoal cohesion and coordinated movement affect the survival of a species: whether to acquire food or evade predators. If the ability for fish to work together is detrimentally affected it could determine the survival of particular species in the oceans of the future. Tropical species may initially fare poorly when moving into new temperate areas,” concluded Professor Nagelkerken.
Mitchell, A., et al. (2021) Ocean warming and acidification degrade shoaling performance and lateralization of novel tropical–temperate fish shoals. Global Change Biology. doi.org/10.1111/gcb.16022.