Inter-decadal Variability of Zooplankton Abundance in the Middle Atlantic Bight

Abstract

Interannual zooplankton abundance trends in the Middle Atlantic Bight region of the US Northeast continental shelf are described and related to variations in environmental variables for the years 1977 to 2009. Depth integrated plankton samples were collected on bimonthly broad-scale surveys of the region. Abundance information indicates that the region’s zooplankton population is flourishing. Total counts and biomass levels have been mostly above average in the second-half of the sampling period. Multivariate analysis of abundance data supported these findings by classifying the time series into three consecutive groups of years defined by varying abundance levels: 1) average in the late 1970s, 2) low in the 1980s, and 3) above average from 1993 to 2009. This analysis identified eleven taxa that had similar increasing interannual abundance patterns during the time series. Evidence is presented that these changes may be related to warming temperatures in the Northwest Atlantic. The increasing abundance levels of the eleven taxa was positively correlated (p<0.01) to surface temperature measurements and the recent trends of the Atlantic Multidecadal Oscillation index. A second, smaller group of six taxa had correlated abundance trends that were variable through the years, with peak production associated with low salinity in the late 1990s.