Northward range expansions are not the full story: A case study of Sabellaria alveolata in Great Britain

Warming oceans are causing changes in the distribution of numerous species. If greenhouse gas production continues to follow current trends, further distribution changes will result. It is often assumed that range shifts into higher latitudes may mitigate threats to susceptible species. Sabellaria alveolata is an important intertidal ecosystem engineer and protected by the UK Biodiversity Action Plan. In this study we created a habitat suitability model for S. alveolata around Great Britain and quantified changes in coastal suitability with increasing sea surface temperatures (SST) using Representative Concentration Pathway (RCP) scenarios modelled by the International Panel on Climate Change. The model included maximum and minimum SST, substrate, slope, kinetic energy due to waves and currents, photosynthetically active radiation, and the coefficient of light attenuation. The model performed very well (AUC = 0.932, 50.2% of deviance explained) and all variables explaining comparable deviance (up to 10%). Recent SST was then combined with predicted SST increases, leading to suitable habitat locations expanding across the southern and western GB coastlines and resulting in larger patches, hence potential for connectivity. Some northern extension was observed; however, this was limited and patchy. The greatest extensions were seen on the south coast, with most of the south coast becoming a continuous network with excellent suitability. With an increase of 1.2 °C, the extent of coast in the excellent suitability class was increased by 5.75% compared to 2020, and by 38.1% with 3.2 °C. Despite the importance of winter temperature in driving S. alveolata distribution, over-riding environmental constraints prevented any major northward migration. The assertion that potential for range shifts to higher latitudes may mitigate the effects of climate change depends on niche availability which may not always be realised. •Sabellaria alveolata is a bioengineer, likely to be impacted by climate change.•We developed a GB wide habitat suitability model for S alveolata.•After substrate, coefficient of light attenuation was the most influential variable.•Warming oceans increased overall suitability of GB coast to S. alveolata.•This demonstrates a sensitivity of sessile marine species to climate change.