UC Marine Council

Coastal fronts are zones of intense biological activity, often defined by a narrow band of flotsam resulting from the convergence of two water masses. The accumulation of zooplankton at fronts has been reported many times in the literature, and is assumed to be the result of passive advection acting on organisms that lack the ability to swim effectively against currents. However, literature on zooplankton swimming behavior,specifically that pertaining to diel vertical migration, demonstrates that certain plankton groups are capable of swimming well over one hundred meters per hour. High rates of primary production are known to occur at fronts, and any behavior by zooplankton that would enhance the movement to and subsequent maintenance in these food sources should be conserved. However, it is unclear whether or not zooplankton aggregations at fronts are controlled exclusively by physical factors, or if behavior plays any role. The focus of this project is to quantify zooplankton abundance and behavior in the vicinity of a seasonally persistent front in Monterey Bay, California. This research is approached in two separate but related studies. The first uses a high-definition digital video camera mounted on a remotely operated vehicle to conduct transects along the Monterey front to visually sample the abundance and swimming orientation of the sea nettle, Chrysaora fuscescens. From initial observations, we hypothesize that sea nettles may be actively swimming towards the front, conceivably to take advantage of the rich feeding opportunity. The second study will address the distribution of smaller zooplankton in the vicinity of the front in an attempt to assess whether or not behavior plays any role in determining the observed distribution. This will be achieved by comparing different groups of zooplankton, for which swimming speeds are known, to that of non-swimming stages, namely fish and invertebrate eggs. Any difference between the distributions of swimming and non-swimming stages should provide a first-order estimate of behavior. These studies will offer further information on the biological dynamics at these important feeding zones.