Time series analysis of interrupted long-term data set (1961-1991) of zooplankton abundance in Gulf of Maine (northern Atlantic, USA)

The main interannual and seasonal signals have been extracted from a multi-decadal data set of zooplankton collected with the Continuous Plankton Recorder in the Gulf of Maine, from January 1961 to December 1991. The monthly abundances of seven species or genera of copepods representing the dominant biomass in the area were considered. The presence of a large consecutive gap (35 months) prevented the use of statistical methods for the prediction of missing data. The eigen-vector filtering (EVF) method was then used on the original time series, while retaining the missing values. For each zooplankton taxon, two principal modes of variability (F-1 and F-2) were extracted, representing the interannual and seasonal variations, respectively. Results of EVF allowed the classification of the different genera or species, according to their main type of variability, into taxa 'interannually dominated' (C finmarchicus, Metridia lucens, Oithona spp.), 'seasonally dominated' (Centropages typicus), and taxa characterized by both 'interannual and seasonal variation' (Pseudocalanus spp., Temora longicornis, Acartia spp.). A comparison between the interannual trends of 'interannually dominated species' and sea surface temperature (SST) indicated that all the species were more or less correlated with this important environmental factor. In particular, a strong negative correlation was found between C finmarchicus and SST at a lag of about 0 months, showing that lower values of SST correspond to higher abundances of Calanus finmarchicus at this latitude. (C) 2001 Ifremer/CNRS/IRD/Editions scientifiques et medicales Elsevier SAS.