Seasonal variations in a deep aggregation of Calanus pacificus in the Santa Barbara Basin

Abstract

A deep aggregation of fifth copepodid (C5) Calanuspacificus in the Santa Barbara Basln (SBB) was mapped over yr w ~t h zooplankton net tows, a n optical plankton counter, and a moored acoushc Doppler current profller Hlgh concentrations of diapausing C5 C pacificus bullt up in the deep waters of the SBB dunng the summer and into the fall Dunng the buddup the deep aggregation moved up from the bottom as oxygen became depleted In the basin S deep waters The deep aggregatlon apparently bullds u p due to the basin trapping C5s that migrate below the sill depth from water advected over the basin C5s are retalned within the basln until they swim or are forced above the sill depth Possible mechanisms responsible for the dispersal of the deep aggregation are mlgratlon to the surface waters with subsequent dispersal by surface currents advection over the basin s sill due to the buildup of oxygen-deficient water or flushing of the basin's deep water