Very Nearshore Oceanography and the Dispersal of Larval Invertebrates

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This study tests the hypothesis that along a rocky coastline nearshore topographically generated secondary circulation affects the cross-shelf dispersal of the larvae of coastal organisms. Secondary circulation may isolate the waters within a small bay from the more offshore waters and my prevent larvae from dispersing out into the coastal waters. Alternatively, it could prevent larvae that have developed in the coastal waters from returning to settlement sites on the shore. These possibilities will be investigated, as well as the underlying patterns and mechanisms. This study would be the first test of these hypotheses.Physical oceanography and concurrent larval distributions associated with topographically generated secondary circulation will be described at sites along the Oregon coast. CTD transects will be taken extending from the beach through the secondary circulation front and out into the coastal waters. Transects of vertical plankton tows will be made concurrently with the CTD sampling to describe the distribution of meroplankton. By affecting larval dispersal, this small-scale circulation could bring about variations in the settlement and recruitment of larvae to the shore. At Sunset Bay, abundance and settlement of cyprids and mussels will be measured at mooring sites across the front at the mouth of the bay. Following the accumulation of animals on settlement plates and brushes will monitor settlement.