Goals and Objectives Relevance of Large-Scale Spatial Studies Questions and Hypotheses MethodsThe coastal ocean off western North American can be divided into at least four regions characterized by differences in wind stress, intensity of coastal upwelling, coastal morphology, freshwater inflow, and the influence of long-term and transient advection, turbulence, and buoyancy. These regions also differ somewhat in terms of the planktonic, benthic and fish assemblages present, the timing of plankton production cycles, feeding and reproductive activity in populations, and the presence or absence of specific life stages of key fish species. Critical mesoscale physical processes may be influenced by future changes in the global atmosphere and ocean, which in turn may impact populations. Regional differences in physical-biological linkages provide a natural laboratory for comparing potential changes in marine populations that may accompany different climate change scenarios.
The large-scale component of a U.S. GLOBEC CCS program will consist of field programs located at multiple sites that characterize and contrast the ecosystem's principal biophysical regions, but may also include large-scale drifter studies, satellite studies, regional numerical models nested in coarser basin-scale models, and the analysis of historical environmental data sets that will connect regions and areas of mesoscale studies. These will tie together comparative studies in the different regions and long-term monitoring. Although it is unrealistic to consider in situ measurements sufficient to monitor the entire latitudinal extent of the CCS, other aspects of the large-scale system can be addressed by comparisons of detailed mesoscale studies in different regions across the large, latitudinal gradients in the system. These include: 1) regions with similar ecosystems but different environmental conditions; 2) the boundaries of distinct biological `provinces' or physical regimes; and, 3) regions connecting the main body of the CCS to sites with long paleosediment records (the Southern California Bight). Investigations of the relation between the timing of life history stages and biological rates with respect to biophysical events are emphasized, as are investigations of genetic variability.
Although an ENSO cannot be guaranteed to occur during the field survey period, the program and monitoring will span the period of a typical El Nino/La Nina cycle. Thus much of the interannual variability observed may be related to that cycle and the field programs should be designed to make use of that variability, and address the following questions. Are El Nino and La Nina the extremes of the spectrum of interannual variability, or are these events unique in their physics and ecosystem impact? Can ecological conditions during ENSOs serve as useful proxies for the ecosystem alterations expected as a result of longer term climatic variability?
The large-scale study tells us something about the entire California Current EBC system, and can be generalized to other EBCs. Interannual variability at the edges of species ranges and transition zones, where the strongest gradients in physical and biological constituents occur, is the best analogy for what might occur if the climate actually shifts. To some degree, the boundaries between physiographic regions correspond with zoogeographic and population boundaries. It is not known to what extent the movement of physical and biological transition regions in response to climate change will coincide. One specific response of the large-scale CCS to climatic changes in local and distant forcing may consist of simple shifts in the locations of the boundaries between the regions, with expansion and contraction of present ranges of species. Species ranges are delimited by either hydrographic/circulation (water mass) restrictions, topographic restrictions, or a combination of the two. Only species whose range is delimited by the first will likely change with changing climate. Species whose current center of population or range limits are determined, at least in part by unique interactions of coastal topography with physical forcing, may not be able to either exploit other habitats or persist in their present habitat with changing environmental conditions, and so will experience a collapse. Latitudinal shifts in these boundaries on interannual to interdecadal time scales provide one model of how climate change affects EBC ecosystems.
Some species (e.g., hake) must cope with processes in more than one CCS region. Although some species appear fixed to specific regions, others migrate along the coast, using different regions as the primary habitat for different life stages; others exist as distinct populations in several locations. An understanding of the linkages between the environment and a population's life cycle must consider significant processes occurring over a broad latitudinal range. Understanding why and how these organisms adapt to conditions in different regimes will provide a better indication of the consequences of climate change to the ecosystem.
Comparative surveys should be conducted in the various physical/biological regions as well as near the transition zones between these regions; the location of these surveys must consider the range and life history of the key species being studied as well as the principal physical processes. For example, comparative studies could examine mesoscale features off central-northern Oregon (Region I), central-northern California (Region II), and the Southern California Bight (Region III). Collaborations with Mexico (Region IV) and Canada (north of Region I) should be established to further examine spatial variability on the largest scales. Transition studies should focus on the boundaries of the biological provinces and the physical regions, while realizing that not all species observe the same boundaries (which may provide useful information in itself). The study also should be part of a large international program whose focus is the comparison of EBC ecosystems.