Effects of two decades of rising sea surface temperatures on sublittoral macrobenthos communities in Northern Ireland, UK

We examined whether two decades of rising sea surface temperatures have resulted in significant changes in the benthic community and frequency of occurrence of Northern and Southern species in three areas of Northern Ireland, using visual census data collected by SCUBA surveys undertaken during two periods: pre-1986 and post-2006. We found little evidence to suggest that rising sea surface temperatures have contributed to the changes in benthic assemblage structure between the pre-1986 and post-2006 surveys. However, there were slight but not significant declines in extreme Northern species at Rathlin Island, and increases in the mean number and frequency of occurrence of extreme Southern species in all three areas. There were also substantial declines in the spatial presence of 7 extreme Northern species and notable increases in distribution of 19 extreme Southern species. In contrast, there were no clear trends in the intermediate to Northern and intermediate to Southern species. These results suggest that rising sea surface temperatures have had significant impacts on the occurrence of rarer marine invertebrate species at the edges of their biogeographic range however the trends differed between areas in Northern Ireland.