A global overview of climate change impacts on freshwater decapods: substantial research gaps across taxa and biogeographic regions

Freshwater decapod crustaceans, with representatives from four main taxonomic groups (Anomura, Astacidea, Brachyura, Caridea), form a large and prominent functional group distributed globally across all types of freshwater habitats. Freshwater decapods play critical ecological roles in aquatic communities and ecosystems, and at the same time have widespread cultural and economic significance. A large proportion of freshwater decapods are imperilled by threats including pollution, habitat loss, invasive species, and importantly, climate change. Direct impacts of climate change, as well as its synergistic effects with other threats, pose a substantial but potentially understudied and possibly even underestimated risk to the conservation of freshwater decapod crustaceans. We assessed patterns of climate change impacts on freshwater decapods, as well as the extent of related research, at a global scale. Based on a comprehensive literature survey of all years up to November 2019, we found that only 49 publications, starting from the first relevant article in 2003, contained empirical evidence of climate change effects on freshwater decapods, with a total of 145 native and 11 non-native freshwater decapod species studied in relation to climate change. Climate-change research has also been increasing for all four groups, but more than half of the literature included the freshwater crayfishes Astacidea. We also found a strong bias towards the Australasian region in climate-change research in freshwater decapods, while no published studies were recorded in the Oceania biogeographic region. Importantly, almost three-quarters of native freshwater decapod species studied were projected/reported to be significantly affected by climate change, while more than 90% of the non-native freshwater decapod species studied were projected/reported to be significantly affected by climate change. Considering the severe impacts demonstrated for several species, and coupled with the notable taxonomic and geographic gaps in research into the rest of the freshwater decapods, there is an urgent need for greater representation in climate-change research across species and in regions of high diversity (such as the Neotropical, Afrotropical, and Indomalayan regions), in order for conservation interventions and measures to be beneficial to the most threatened groups.