Zooplankton trends: US north-east shelf ecosystem and adjacent regions differ from north-east Atlantic and North Sea

A multidecadal time series of zooplankton collected with the continuous plankton recorder from six subareas within the US north-east shelf ecosystem, and adjacent regions, was examined. The methods of data collection and analyses were identical to those used by the Sir Alister Hardy Foundation for Ocean Science (Foundation), Plymouth, England. Researchers at the Foundation reported long-term declines in zooplankton abundance for the north-east Atlantic as shown by principal component analyses. Using identical analytical methods, we find an increasing trend in Calanus finmarchicus (Gunner, 1765) abundance between 1961 and 1989. Other taxonomic groups showed no consistent, long-term trend in abundance. It appears that zooplankton of the north-east Atlantic and the US north-east shelf ecosystem are responding to different environmental forcing functions during the past decades.