The relationship between Gulf Stream position and copepod abundance derived from the Continuous Plankton Recorder Survey: separating biological signal from sampling noise

Abstract

The mean annual abundance of copepods was calculated from Continuous Plankton Recorder records for the period 1966-1992, and for an area to the north of the UK bounded by latitudes 58-64°N and longitudes 3°E and 21°W. Spatial heterogeneity of copepod abundance, when combined with changing tow routes, introduced considerable noise as well as an artifactual increasing trend in copepod abundunce into the time series. We therefore defined a more homogeneous subarea spanning ˜270 km either side of the shelf edge between latitudes 59 and 6I°N, within which the noise introduced by changing tow routes was considerably less. There was a significant (P < 0.01) positive linear relationship between the annual copepod abundance for this small homogeneous subarea and the annual Gulf Stream position between longitudes 79 and 65°W. The copepod abundances for the last 4 years of the time series (1989-1992) were, however, significantly (P < 0.01) lower than those predicted from the Gulf Stream position in these years. Evidence suggests that the anomaly of these years was not an artifact caused by poor sampling or changing tow speeds.