THE INFLUENCE OF SPATIALLY AND TEMPORALLY VARYING OCEANOGRAPHIC CONDITIONS ON MEROPLANKTONIC METAPOPULATIONS

We synthesize the results of several modeling studies that address the influence of variability in larval transport and survival on the dyna mics of marine metapopulations distributed along a coast. Two importan t benthic invertebrates in the California Current System (CCS), the Du ngeness crab and the red sea urchin, are used as examples of the way i n which physical oceanographic conditions can influence stability, syn chrony and persistence of meroplanktonic metapopulations. We first exp lore population dynamics of subpopulations and metapopulations. Even w ithout environmental forcing, isolated local subpopulations with densi ty-dependence can vary on time scales roughly twice the generation tim e at high adult survival, shifting to annual time scales at low surviv als. The high frequency behavior is not seen in models of the Dungenes s crab, because of their high adult survival rates. Metapopulations wi th density-dependent recruitment and deterministic larval dispersal fl uctuate in an asynchronous fashion. Along the coast, abundance varies on spatial scales which increase with dispersal distance. Coastwide, s ynchronous, random environmental variability tends to synchronize thes e metapopulations. Climate change could cause a long-term increase or decrease in mean larval survival, which in this model leads to greater synchrony or extinction respectively. Spatially managed metapopulatio ns of red sea urchins go extinct when distances between harvest refugi a become greater than the scale of larval dispersal. All assessments o f population dynamics indicate that metapopulation behavior in general depends critically on the temporal and spatial nature of larval dispe rsal, which is largely determined by physical oceanographic conditions . We therefore explore physical influences on larval dispersal pattern s. Observed trends in temperature and salinity applied to laboratory-d etermined responses indicate that natural variability in temperature a nd salinity can lead to variability in larval development period on in terannual (50%), intra-annual (20%) and latitudinal (200%) scales. Var iability in development period significantly influences larval surviva l and, thus, net transport. Larval drifters that undertake diel vertic al migration in a primitive equation model of coastal circulation (SPE M) demonstrate the importance of vertical migration in determining hor izontal transport. Empirically derived estimates of the effects of win d forcing on larval transport of vertically migrating larvae (wind dri ft when near the surface and Ekman transport below the surface) match cross-shelf distributions in 4 years of existing larval data. We use a one-dimensional advection-diffusion model, which includes intra-annua l timing of cross-shelf flows in the CCS, to explore the combined effe cts on settlement of: (1) temperature- and salinity-dependent developm ent and survival rates and (2) possible horizontal transport due to ve rtical migration of crab larvae. Natural variability in temperature, w ind forcing, and the timing of the spring transition can cause the obs erved variability in recruitment. We conclude that understanding the d ynamics of coastally distributed metapopulations in response to physic ally-induced variability in larval dispersal will be a critical step i n assessing the effects of climate change on marine populations.