Long-term comparison of soft bottom macrobenthos in the Bay of Banyuls-sur-Mer (north-western Mediterranean Sea): A reappraisal

Abstract

The macrofauna of the Bay of Banyuls-sur-Mer, initially sampled in 1967–1968 and revisited in 1994, was re-sampled again in 2003, using the same gear and techniques. Results allowed us to overcome some of the flaws of a previous long-term comparison (i.e. between 1967–1968 and 1994). Our data confirm major changes (increase in species richness and changes in macrofauna composition) already observed between 1967–1968 and 1994. The most important changes observed during that period were the increase of the polychaete Ditrupa arietina within the Spisula subtruncata and Nephtys hombergii communities, and the decrease of the polychaetes Scoloplos armiger and Notomastus latericeus in the S. armiger community. Temporal changes in macrofauna composition followed the same general pattern within both the S. subtruncata and the N. hombergii communities. Macrofauna compositions recorded in 1967–1968 and 1994 differed most and the ones recorded in 2003 were intermediate. Temporal changes in abundances of dominant species within these two communities were clearly opposite between 1967–1968 and 1994 compared to 1994 and 2003. Both S. subtruncata and N. hombergii communities are submitted to re-suspension events induced by storms. Strong re-suspension events in the Bay of Banyuls-sur-Mer were hind-casted from 1965 to 2005 based on meteorological data using two procedures calibrated on a one-year time series of wave measurements. Their frequency negatively correlated with the North Atlantic Oscillation (NAO) annual index. The 1994 survey corresponded to a period characterised by a high NAO index and a low number of strong re-suspension events especially during spring, which is the period of recruitment of D. arietina. These observations are consistent with the occurrence of a bottleneck immediately after recruitment, which may account for instability of the population dynamics of this particular species. Temporal changes in macrofauna composition within the deepest S. armiger and Venus ovata communities were characterised by important differences between 1967–1968 and 1994 and almost identical compositions in 1994 and 2003.