Fucoid assemblages on the north coast of Spain: past and present (1977-2007)

Fucoid assemblages dominated by Pelvetia canaliculata, Fucus spiralis, F. vesiculosus, and Ascophyllum nodosum located at two sites on the central coast of Asturias (northern Spain) were sampled monthly in 1977. Repeating the same sampling methodology, a resurvey was done in 2007 to detect changes in the abundances of the species using the previous data as a baseline. Annual net primary production was lower for all the species in 2007, and there were differences in the timing of maximum biomass for P. canaliculata and F. vesiculosus, as well as a shortening of the growth period in 2007. Associated fauna also differed between dates. Higher abundances of Gibbula spp. occurred in 2007, whereas littorinid species densities in the upper intertidal were reduced in that year. As a result, the fucoid-grazers balance changed, with P. canaliculata and particularly F. vesiculosus, being the assemblages most sensitive to change. Observed modifications were not merely fluctuations in the biomass patterns of these species, but also responses to increases in air temperature and sea surface temperature and to a shift in the frequency and seasonality of upwelling episodes. Other long-term abiotic fluctuations not directly related to global warming should also be considered as possible drivers for these changes.