Abstract
Zooplankton community analyses in Massachusetts Bay (Gulf of Maine, USA) from 1998 to 2008 with 102 mu m mesh nets revealed seasonal and interannual variability in zooplankton abundance, with maxima in summer and minima in winter. Zooplankton was dominated by copepod nauplii, copepodites and adults, mostly of the small cyclopoid copepod Oithona similis. Time-series analyses revealed a multi-year decline in total zooplankton abundance from 2000 to 2008, especially due to declines in Oithona similis and Pseudocalanus spp. This decline was not exhibited by barnacle nauplii and Calanus finmarchicus. There were no significant relationships between surface or mean water column temperature and salinity for any zooplankton group except for significantly higher abundances of C. finmarchicus at higher surface salinity. There was a significant positive correlation between total zooplankton abundance and integrated chlorophyll. The decline in zooplankton abundance since 2000 was not obviously related to diversion of sewage effluent from the Boston Harbor outfall to Massachusetts Bay, or to natural hydrographic variability. The zooplankton decline in Massachusetts Bay highlights the importance of multi-year sampling to characterize interannual variability. Comparisons of our results with those of other programs in the Gulf of Maine are complicated by differences in sampling net meshes, but our results shared some similarities with other studies during years when these studies overlapped with ours. In particular, small copepods declined in abundance beginning around 2000-2001, Calanus finmarchicus was abundant and salinities were high during 2002 through 2004, and zooplankton and chlorophyll levels declined from 2000 through 2004.