Corals worldwide are threatened by global warming, in turn threatening fish species that rely on them to provide food, habitat and shelter from predators. A study published in Proceedings of the Royal Society B: Biological Sciences suggests that in many areas fish biodiversity could be halved as a consequence of coral decline.
Giovanni Strona, from the University of Helsinki, led an international team including Italian researchers from L’Aquila, Naples and Milan, in a study1 to assess to what extent fish diversity really depends on coral diversity. The researchers took maps of the world’s main reef regions, and divided them into a grid of cells measuring one latitudinal per one longitudinal degree. They mapped fish and coral diversity inside each cell, by collating data from online databases compiled by the International Union for the Conservation of Nature, an NGO. They looked at 6964 coral-reef-fish species and 119 coral genera.
The scientists created a mathematical model to investigate how fish diversity varies in relation to coral diversity, taking into account factors such as salinity, temperature, and reef isolation. With this model, they looked at three of the scenarios described in the latest Intergovernmental Panel on Climate Change (IPCC) assessment to understand how, in relation to climate change, the expected future loss of corals would affect fish biodiversity.
Rising water temperatures are known to cause bleaching, the expulsion of symbiotic algae by coral polyps which results in starvation. The scientists assumed a substantial coral mortality in a given reef locality at a given time if the projected temperature was two degrees higher than the historical average.
Under the most pessimistic climate scenario, all reefs on a global scale will be affected by at least one mass mortality event by 2060. Under the most optimistic one, the share would still be above 60%. The study concludes that in the pessimistic scenario local fish diversity would decline by 40% by 2060. This represents more than the fish that actually live on reefs, indicating that many other species would be indirectly affected.
One limitation of the model is that it does not reveal much about which fish species will be more affected, and the team is now focusing on this aspect. “Unraveling such complexity may be vital for preventing future biodiversity loss” says Strona.
"This study describes a refined theoretical framework on the link between community and habitat which could be used in other contexts,” says Stefano Aliani, a marine biology researcher at the ISMAR-CNR Institute of Marine Sciences, in Venice, who did not take part in the research.
Strona G et al., Proc. R. Soc. B 288 (2021).