| The accumulation of zooplankton at fronts have been known to science for centuries, however zooplankton behavior is generally under-appreciated as a factor contributing to the observed aggregation.{09}I observed distributional patterns of various zooplankton species near the Monterey Bay upwelling shadow front and in the nearshore zone of Santa Monica Bay, California, in an effort to estimate the extent to which behavior determines horizontal distributions near fronts.; Using high-definition digital video on a remotely operated vehicle, I quantified the distribution and swimming orientation of sea nettles near the Monterey front. Sea nettles were highly aggregated on the front, and were more abundant on the warmer northern side of the front compared to the colder southern side. Regardless of proximity, sea nettle swimming orientation was generally directed towards the front, implying that the frontal aggregation was due in part to swimming behavior.; Zooplankton and water property data were gathered along three transects crossing the Monterey front. The distribution of fish and invertebrate eggs, which were passive tracers, revealed that the front was strongly convergent on two transects, but exhibited transverse shear flow along the third transect where eggs skewed away from the front. Despite differences in flow patterns along the transects, zooplankton aggregations always occurred along the front. Thus, at least at the transverse shear front, behavior must account for some of the distributional bias on the front.; A characterization of the nearshore zone off Dockweiler State Beach, Santa Monica Bay, was made using shipboard and in-water sampling of water properties and zooplankton net tows. A conspicuous difference in flow patterns was revealed between water shoreward of the 10-20m isobath, where water moved alongshore with a tidal periodicity and no net directional flow, and that offshore, where water traveled alongshore in one direction over time. The observed separation of inner and outer waters was corroborated by data on plankton species distributions. Most species were skewed in either the onshore or offshore direction, suggesting that species are generally confined to the water mass of their respective sources, and that there could be a reduction in onshore-offshore mixing between the 10-20m isobath. |
