Did global warming and alien invasions affect surf zone hyperbenthic communities on sandy beaches in Belgium?

Due to global warming, southern hyperbenthic species were expected, which extend their distribution range northwards. It was also expected that alien species would have invaded the surf zone hyperbenthos. Therefore, the species composition of the hyperbenthos occurring along the Belgian coast was determined, and spatial and temporal patterns in community composition were assessed. The hyperbenthos was sampled with a hand-pushed sledge on 10 sandy beaches during summer 1995, winter 1996, summer 2009 and winter 2010. Neither alien species nor any southern species which recently extended its distribution range northwards were observed during the present study, indicating that alien species and global warming did not yet affect the species composition of the surf zone hyperbenthos along the Belgian coast. The hyperbenthic community was dominated by Mysida, while Amphipoda were the most diverse group. Multivariate analysis revealed that temporal patterns dominated over spatial patterns: winter and summer hyperbenthic communities clearly differed in species composition and different species assemblages were also observed between the first and the recent sampling campaigns. Although for several other groups, a decline in species richness has been observed closer to the mouth of the Westerschelde, no spatial gradient could be recognised for the surf zone hyperbenthos. Instead, it was found that species richness was positively related to beach width. It could be concluded that the species composition and the total abundance of surf zone hyperbenthic communities along sandy beaches of the Belgian coast strongly vary in space, but especially in time.