Authors: P. da Silva, Janine; Gonçalves, Duarte Vasconcelos;Lopes-Lima, Manuel;Anastácio, Pedro M.;Banha, Filipe;Emmanuel, Frimpong;Gama, Mafalda;Miranda, Rafael;Reis, Joaquim;Filipe, Ana Filipa;

The freshwater pearl mussel Margaritifera margaritifera has been suffering major population declines in Europe. This endangered species is a host specialist and exclusively requires salmonid species (Salmo trutta and Salmo salar) to complete its life cycle, demanding a special conservation attention, particularly under future climate change. To evaluate the importance of including the occurrence of fish hosts for predicting the current and future distribution of M. margaritifera in Europe, three datasets were used to build species distribution models (SDMs) with a maximum entropy (MaxEnt) approach: (1) environmental variables; (2) probability of fish hosts occurrence; and (3) environmental variables and probability of fish hosts occurrence. Projections were also used to evaluate the adequacy of current networks of European protected areas in covering suitable habitats. Incorporating data about fish hosts into M. margaritifera’s SDMs avoided the overprediction of geographical projections. While predictions indicated large contractions in M. margaritifera's distribution as a result of future climate change, the current European network of protected areas fails to safeguard its habitats. SDMs can inform political decision-making about the likely scenarios for species occurrence in future decades, the requirements needed for an effective conservation strategy, and the regions where conservation should be a priority.