Shifts in neritic copepod communities off the Basque coast (southeastern Bay of Biscay) between 1998 and 2015

The interannual variations in absolute and relative densities of copepods from the neritic waters of the southeastern Bay of Biscay and their relationship to climate teleconnections and local environmental factors were assessed using time series for the 1998-2015 period. Opposite patterns of variation of the absolute densities of spring Acartia clausi and Centropages typicusspecies vs. summer/autumn species, mainly Oncaea media, but also Ditrichocorycaeus anglicus, Oithona nana, Temora stylifera, and Oithona plumifera were detected. This type of opposite patterns were also observed between the relative densities of the spring A. clausi and summer Paracalanus parvus species. These opposite density patterns were positively correlated to all seasons North Atlantic Oscillation (NAO), spring East Atlantic pattern (EA), summer and autumn water temperature and summer chlorophyll a. They were negatively correlated to summer EA pattern, the winter and spring Atlantic Multidecadal Oscillation (AMO) and water temperature, and the upwelling index of all seasons. In these patterns of copepod variation two regime shifts were detected, one in 2008 towards an increase in the spring species and the other one in 2014-2015 towards an increase of summer species. This latter regime shift coincides in time with the abrupt community shifts predicted in the literature for 2014.