Interaction of physical and biological processes in the settlement of planktonic larvae

Planktonic larvae are at the mercy of the currents for their approach to settlement sites. The presence of planktonic larvae at any given location is a random process. Time-series data for phytoplankton suggest that the characteristic time for a plankton patch to be at a given coastal location is about a week. Once at a settlement site, the interaction of physical processes and biological responses determines the spatial pattern of settlement. For example, where larvae settle when they encounter a kelp bed depends on the current speed, vertical larval distribution, and larval behavior. Simple calculations of settling by abalone larvae suggest that their concentrations in the water could be halved within 100 m of entering a kelp bed. The faster currents of a kelp-free area would extend this distance to about a kilometer. This interaction of the physical and the biological is an important aspect of larval ecology.