The dynamics of barnacle species inhabiting the rocky intertidal zone of central California are analyzed using an advection—diffusion model for barnacle larvae coupled to a space—limited model for barnacle adults. The model explores the link between physical transport processes and the population dynamics of coastal barnacle species and inspects the hypothesis that recruitment events result from the collision of upwelling fronts with the intertidal zone. Initially, a one—dimensional model is presented that incorporates eddy diffusion, offshore advection, and an offshore reflecting boundary representing an upwelling front. Physical movement of the front, in response to fluctuating upwelling, is modeled by varying the position of the reflecting boundary. Results show analytically that populations can sustain only very low levels of offshore flow when not bounded by an offshore front, and that increased advection can cause a population to go extinct. The criterion for population viability is dependent upon the strength of advection and position of the offshore front. The one—dimensional model is subsequently extended to two dimensions to allow for the spatial distribution of both larvae and adults in a more realistic context. Recruitment patterns, adult dynamics, and larval distribution patterns are loosely based on parameters from the study area bounded between the Monterey Peninsula and Point Sur. Upwelling/relaxation events are phenomenologically incorporated into the model by varying the position of the offshore boundary and the magnitude of cross—shelf advection. The analysis shows how the interaction of advective and diffusive processes and the location of the offshore front determines the dynamics of coastal barnacle populations. The two—dimensional model represents the next step toward assimilation of time—dependent remote sensing data and/or linking to numerical circulation models.

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Ecological systems at both population and com m unity scales are recognized increasingly as being more open than previously thought. In coastal m arine systems, physical oceanographic processes affecting larval stages are as, or more important than, biological interactions affecting adults. In terrestrial systems, the membership in ecological communities is controlled by geologic transport processes as much as by species interactions. Hence ecological science has become increasingly an earth science, and less a biological science. The differences between marine and terrestrial ecosystems imply that terrestrial systems are more localized functionally than marine systems; more likely to suffer extinction from habitat loss; and less likely to recover upon removal of stress. In addition, damage to a marine system is more likely to be felt further from the source of stress than it would in a terrestrial system. Finally, harvesting strategies at sea should react to continuous environmental monitoring whereas on land, demographically based strategies of harvest can suffice.

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