Decadal Distribution and Abundance Trends for the Late Stage Copepodites of Pseudocalanus spp. (Copepoda: Calanoida) in the US Northeast Continental Shelf Ecosystem.

The average annual cycle of abundance and the bimonthly distributions of the copepod Pseudocalanus spp. are described for U.S. Northeast continental shelf waters from samples collected on broad-scale plankton surveys 1977–2012. Population levels begin to increase during January–February, surge in March–April, and peak throughout the region during May–June. The copepod’s population density declines sharply after June and becomes minimal from September–December. Spatially, seasonal high levels persist throughout the year in coastal waters surrounding and adjacent to the Cape Cod peninsula. During late spring, dense concentrations are found in Gulf of Maine coastal waters and in a high abundance band that extends southwestward from Georges Bank into the northern half of Middle Atlantic Bight waters. Pseudocalanus spp. interannual abundance variability was substantial; displaying several extended low and high periods through the time series. In general, numbers were high from the late 1970s through the early 1980s, low in the mid-1980s, elevated in the 1990s, and low again in the 2000s. This pattern was correlated negatively with temperature and positively with phytoplankton abundance trends. It is proposed that the copepods low abundance in the 2000s may have been caused by warmer temperatures that indirectly depressed the abundance of phytoplankton that this copepod uses for food. Survey data also indicate that predation pressure from salps and perhaps some additional species may contribute to the precipitous summer decline of Pseudocalanus spp. The copepod’s abundance was found to be independent from the climatic variation associated with either the North Atlantic or Arctic Oscillation.