Considering biotic interactions exacerbates the predicted impacts of climate change on coral-dwelling species

Aim: Climate change is affecting the geographic distributions of many species and researchers are increasingly relying on species distribution models (SDMs) to forecast species' redistributions under climate change. Such modelling studies, however, often ignore biotic interactions that shape species' geographic ranges. This is especially problematic for coral reefs, which host a high diversity of species and interactions. We tested how biotic interactions affect the distribution patterns of obligate coral-dwelling Trapezia crabs. Location: Global coastal ocean. Time Period: 2000-2014, 2040-2050, 2090-2100. Major Taxa Studied: Corals and coral-dwelling Trapezia crabs. Methods: We determined the symbiotic relationships between 22 crab species in the genus Trapezia and corals via field survey and extensive literature review. We first developed SDMs for coral and crab species using exclusively abiotic variables (abiotic-only models for corals and crabs). Then we constructed a second set of models where we accounted for coral distributions into crab predictions by combining model predictions for the two taxa a posteriori (abiotic-plus-biotic models for crabs only). Results: We obtained 30 commonly accepted coral-crab symbiotic relationships from nine Trapezia crab and six stony coral species. The abiotic-only model predictions showed that six corals may lose approximately one-sixth of suitable ranges under RCP 8.5 in 2040-2050. The two types of models for crabs yielded largely different habitat suitability predictions and accounting for biotic interactions into SDM predictions exacerbates the predicted impacts of climate change on coral-dwelling crabs. Main Conclusions: Our results show large discrepancies in crab spatial distribution patterns with and without accounting for symbiotic interactions. Our findings highlight the important role of modeller's decision on accounting for biotic interactions when predicting the geographical ranges of coral-dwelling species, with important implications for designing future conservation and management strategies for marine species.