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Larval supply of meroplanktonic larvae in relation to behavioural strategies
Gunnar Brandt
ICBM, University of Oldenburg
brandt@icbm.de(Abstract received 05/01/2005 for session A)
ABSTRACT
A three-dimensional Individual-Based Model (IBM) including the Lagrangian solution for the advection-diffusion equation and formulations for temperature-dependent development and vertical movement is used to simulate the fate of larvae of the Blue Mussel (Mytilus edulis) in the German Bight (North Sea). Simulations were carried out for different spawning dates during spring of the years 2000 to 2004. Passive drifting results in an export of more than 70% of all individuals to unsuitable offshore areas due to high turbulence and a counterclockwise tidal residual flow. The spawning date within the year and, thus, the development time has only very limited influence on larval supply to potential settlement areas. Diurnal vertical migration (upward at night, downward at daytime) is often proposed for various planktonic species to enhance retention in vertical sheared flows. Since the tidal and diurnal period differ slightly diurnal migration only gradually improves the return probabilty to coastal waters. In contrast, vertical swimming that is induced by salinity changes (upward at increasing, downward at decreasing values of salinity) leads to significantly higher values for return and retention exceeding 75% for a maximum swimming velocity of 6mm/s. The success of this behavioural strategy is based on the ubiquitary coastal salinity gradient with higher values offshore and the resulting oscillations of salinity values in phase with the tides. Despite the coarse resolution of the hydrodynamic model used in this study the results robustly explain retention in tidal areas and thus propose a potential mechanism for mobile planktonic species to effectly influence patterns of dispersal.
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2005 LAPCOD Meeting, Lerici, Italy, June 13-17, 2005