ZOOPLANKTON COMMUNITY PATTERN ASSOCIATED WITH A CALIFORNIA CURRENT COLD FILAMENT

In July 1988 we sampled upper layer zooplankton distributions in and around a major cold filament located off Point Arena, California. Average zooplankton biomass levels declined inshore to offshore, but relatively high levels extended seaward along the cool side of the filament jet. A series of transverse station lines shows strong shifts in community composition across the axis of the filament. The cross-filament compositional sequence was recognizably similar along each line, giving an impression (supported by cluster analysis and along-flow versus cross-flow spatial autocorrelation) of banding parallel to the filament axis. The "standard" sequence was characterized by local maxima of Dolioletta gegenbauri in nonfilament waters to the south and east, Euphausia pacifica along the southeast margin of the filament, Eucalanus californicus and euphausiid larvae within the cool core of the filament and extending partway across the strong seaward jet on the north and west margin of the filament, and heteropod larvae, chaetognaths, Dolioletta, and a mixture of small copepods (including several with southern and offshore faunal affinities) along the warm side of the jet and extending into nonfilament waters to the north and west. A "core" group of samples characterized by high abundance of Eucalanus matched the trajectories of drifters released at the upstream end of the filament. Both crossed geopotential anomaly contours (to larger phi) as they moved out the filament, suggesting a cross-jet component of motion.