Warming-related shifts in the distribution of two competing coastal wrasses

• We investigated how temperature may affect the distribution of two antagonist wrasses.
• We compiled an extensive database of patterns of distribution at 346 Mediterranean sites.
• Thalassoma pavo dominates shallow waters at warmest sites, where Coris julis locates deeper.
• Northernmost shallow sites are dominated by C. julis, where T. pavo is scarce.
• C. julis progressively will restrict its distribution range.

Warming induces organisms to adapt or to move to track thermal optima, driving novel interspecific interactions or altering pre-existing ones. We investigated how rising temperatures can affect the distribution of two antagonist Mediterranean wrasses: the ‘warm-water’ Thalassoma pavo and the ‘cool-water’ Coris julis. Using field surveys and an extensive database of depth-related patterns of distribution of wrasses across 346 sites, last-decade and projected patterns of distribution for the middle (2040–2059) and the end of century (2080–2099) were analysed by a multivariate model-based framework. Results show that T. pavo dominates shallow waters at warmest locations, where C. julis locates deeper. The northernmost shallow locations are dominated by C. julis where T. pavo abundance is low. Projections suggest that the W-Mediterranean will become more suitable for T. pavo whilst large sectors of the E-Mediterranean will be unsuitable for C. julis, progressively restricting its distribution range. These shifts might result in fish communities’ re-arrangement and novel functional responses throughout the food-web.