Streams in the Mediterranean Region are not for mussels: Predicting extinctions and range contractions under future climate change

Climate change is becoming the leading driver of biodiversity loss. The Mediterranean region, particularly southwest-ern Europe, is already confronting the consequences of ongoing global warming. Unprecedented biodiversity declines have been recorded, particularly within freshwater ecosystems. Freshwater mussels contribute to essential ecosystem services but are among the most threatened faunal groups on Earth. Their poor conservation status is related to the de-pendence on fish hosts to complete the life cycle, which also makes them particularly vulnerable to climate change. Species Distribution Models (SDMs) are commonly used to predict species distributions, but often disregard the poten-tial effect of biotic interactions. This study investigated the potential impact of future climate on the distribution of freshwater mussel species while considering their obligatory interaction with fish hosts. Specifically, ensemble models were used to forecast the current and future distribution of six mussel species in the Iberian Peninsula, including envi-ronmental conditions and the distribution of fish hosts as predictors. We found that climate change is expected to se-verely impact the future distribution of Iberian mussels. Species with narrow ranges, namely Margaritifera margaritifera and Unio tumidiformis, were predicted to have their suitable habitats nearly lost and could potentially be facing regional and global extinctions, respectively. Anodonta anatina, Potomida littoralis, and particularly Unio delphinus and Unio mancus, are expected to suffer distributional losses but may gain new suitable habitats. A shift in their distribution to new suitable areas is only possible if fish hosts are able to disperse while carrying larvae. We also found that includ-ing the distribution of fish hosts in the mussels' models avoided the underprediction of habitat loss under climate change. This study warns of the imminent loss of mussel species and populations and the urgent need of management actions to reverse current trends and mitigate irreversible damage to species and ecosystems in Mediterranean regions.

Automated summary

Climate change is the leading cause of biodiversity loss, especially in the Mediterranean region. Freshwater mussels, important for ecosystem services, are highly threatened due to their dependence on fish hosts and their vulnerability to climate change. This study predicts severe impacts on the distribution of mussel species in the Iberian Peninsula, with some species facing regional and global extinctions.