Scientists have developed a model that predicts that six tropical fish species will expand into northern Japan as sea temperatures rise.
A new study predicts how global climate change will affect tropical fish species in Japan. The research, published in the journal Boundaries in the Built Environmentt, predicts that six species of tropical fish will expand northward into the temperate regions of the Japanese coast as sea temperatures rise.
Climate change is causing temperate coastal waters to warm, affecting the abundance, distribution and types of marine species that live there. In Japan, water temperature in coastal regions has risen by 1.16°C degrees over the past 100 years, double the global average of 0.56°C degrees.
Tropicalization – the increase in the number of species native to tropical waters – will affect humans in several ways. For example, the growing number of toxic pest species can be detrimental to fishing and recreation, increasing the risk of food poisoning or injury when swimming. Increasing numbers of herbivorous fish can lead to loss of seagrass beds and algal beds, reducing carbon uptake. On the other hand, the increasing numbers of tropical reef fish may attract tourism and provide opportunities for the aquarium fish trade and environmental education.
“Our current knowledge of how marine ecosystems in Asia will respond to climate change is limited, especially for coastal fish species,” says Kenji Sudo, a marine ecologist at Hokkaido University. “We developed a model to study how tropical fish in Japan might respond to changing environmental conditions.”
The Hokkaido researchers selected six species of tropical fish from among the 4,500 species of fish that inhabit Japanese waters. They chose species that represent a range of different effects on humans and whose numbers are well documented. They studied two poisonous noxious fish (Alterus scriptus and Scarus ovifrons), two herbivorous fish (Cyphosus bigibbus and Siganus fuscescens), and two tropical reef fish (Amphiprion frenatus and Chaetodon auriga).
The researchers used publicly available distribution data and numerical models to estimate how the future habitats of the six species might change under different climate change scenarios. They examined how different environmental variables, such as minimum sea surface temperature, depth, slope, coral reef area and seagrass/seabed areas, affect fish species patterns and used this information to predict future changes.
They found that minimum sea surface temperature was the most important factor affecting distribution patterns for all species. Depth, slope and seagrass/seaweed beds were also important for some species.
The model showed that under two different carbon emission scenarios, the six tropical species were expected to expand into the central and northern regions of Japan. In the 2090s, their range was estimated to expand to about 1.5 times that of 2000-2018 with severe warming. The expansion was expected to be highest along the Pacific coast, which is affected by the warm Kuroshio and Tsushima currents along the Sea of Japan coast. However, the model indicated that changes in habitat range could be minimized by rigorous mitigation measures.
“The results indicate that many human activities along the Japanese coasts, such as fishing, recreation and human health, can be strongly affected by changes in tropical fish patterns without appropriate climate change mitigation measures. “, says co-author Masahiko Fujii, associate professor. at the Faculty of Environmental Earth Sciences, Hokkaido University.
The study suggests that an ambitious commitment to reduce greenhouse gas emissions could prevent future tropicalization. The model could be used by local decision makers to plan appropriate climate adaptation programs.