Martinho Marta-Almeida, Jesús Dubert, Álvaro Peliz, Henrique Queiroga

Influence of vertical migration pattern on retention of crab larvae in a seasonal upwelling system

Henrique Queiroga, Maria Joao Almeida, Teresa Alpuim, Augusto A. V. Flores, Sara Francisco, Ignácio Gonzàles-Gordillo, Ana Isabel Miranda, Inês Silva, José Paula

Tide and wind control of megalopal supply to estuarine crab populations on the Portuguese west coast

Crab larvae are able to perform vertical migrations of several tens of meters in synchrony with the day cycle, thereby being exposed to depth-varying currents. Coastal upwelling circulation is characterised by a surface water layer with a seaward flow superimposed on a deeper layer where a landward counter-current develops. Results of a numerical model show that, by partitioning time between the two layers in a cyclic way, crab larvae enhance retention on the inner shelf. This mechanism may be especially useful at topographically smooth coasts lacking areas where larvae will be retained nearshore over larger time periods. The existence of a pool of larvae in nearshore waters increases the likelihood of onshore and up-estuary transport by biophysical processes.

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