oa Arabian Gulf reef fishes: a valuable but vulnerable asset for climate change research

The Arabian Gulf is one of the most thermally extreme marine environments on earth, representing a unique ‘natural laboratory’ in which to develop an understanding of how reef fishes may respond to future climate change. Recent research comparing fish in the southern Arabian Gulf with those on reefs in the more benign Gulf of Oman and Arabian Sea has provided insights into how reef fish communities, populations and individuals may respond to increasingly extreme temperatures in other regions. Reef fish communities in the southern Arabian Gulf were shown to be low in species diversity, abundance, and biomass compared with those on reefs in less extreme environments. Arabian Gulf reef fish communities were also functionally distinct, with coral-dependent fishes and important functional groups such as parrotfish being relatively rare. Demographic studies of several species have shown that the extreme thermal environment of the southern Gulf is associated with faster growth rates than conspecifics outside of the Gulf, but that these fish mature at significantly smaller sizes, which may have implications for reproduction and population replenishment. Such studies can provide insight into how populations and communities in other regions may respond as sea temperatures increase in the future. While Arabian Gulf reef fish represent a valuable asset for understanding biological responses to extreme temperatures, they are not immune to the growing pressure of climate change in the region itself. Recent experiments have shown that while Arabian Gulf reef fishes may have the capacity to survive higher temperatures than conspecifics in surrounding seas fish in the Gulf are living very near their physiological limits, suggesting that they are likely to be highly susceptible to even modest increases in seawater temperature. Climate change is also likely to have indirect effects on reef fishes in the Gulf through increased habitat loss, with all coral dependent fishes known for the Gulf already classified as vulnerable to extinction as a result of reef degradation in recent decades. There are also considerable gaps in knowledge of how ocean acidification may affect reef fishes, particularly the more vulnerable larval stages, and how this may synergize with thermal and other anthropogenic stressors.