Speaker: Alan Shanks, OIMB, University of Oregon
Topic: In the intertidal zone, subsidies (larval settlers and phytoplankton food) and community structure are profoundly influenced by surfzone hydrodynamics
The size of bottom-up subsidies, food and larvae, from the ocean has a profound impact on intertidal community structure and populations. Alongshore variations in subsidies have been attributed to variation in coastal oceanographic conditions, but also might be due to variations in surfzone hydrodynamics. We have tested this hypothesis in a variety of ways. What we have found is 1) the concentrations of larval settlers and coastal phytoplankton are significantly and one or more orders of magnitude higher in more dissipative than more reflective surf zones, 2) the concentrations of larval settlers and coastal phytoplankton are more than an order of magnitude lower in more reflective surf zone than in the waters just seaward of the surf zone, 3) the settlement of barnacles is orders of magnitude higher in more dissipative than reflective surf zones, 4) barnacle populations structure varies with surfzone hydrodynamics – population densities are orders of magnitude higher at more dissipative surf zones, 5) growth and reproductive output of barnacles and mussels varies with surfzone hydrodynamics – growth rates and reproductive output are far higher at more dissipative than reflective surf zones, 6) densities of benthic macro-algae are far higher at more reflective than dissipative surf zones. Surfzone hydrodynamics is a major driver of intertidal community structure and function. The effect of surfzone hydrodynamics appears to be far larger than alongshore variation in coastal oceanographic conditions. Even over short alongshore distances (10s to 100s of meters) communities vary with the hydrodynamics of the adjacent surf zone.
Thursday, April 11 at 3:30pm to 4:30pm
Hatfield Marine Science Center, Guin Library Seminar Room
2030 SE Marine Science Dr, Newport, OR 97365
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