Introduction

# SECTION II-INTRODUCTION

The U.S. GLOBEC (Global Ocean Ecosystems Dynamics) program seeks to understand how global climate change affects the distribution, abundance, production and population dynamics of animals in the sea. One type of climate change is the natural variability on scales of years to centuries. Anthropogenic changes in atmospheric circulation, such as those caused by increased concentrations of greenhouse gasses, will cause additional changes in the ocean's temperature and current fields. Although the pattern and magnitudes of these changes are not known, scientists do know that during past glacial periods the locations of major ocean currents were significantly different from their present positions. Thus, the climatic changes associated with increased concentrations of greenhouse gasses are expected to include displacements and changes in the strength of ocean currents. These will cause significant local changes in climate and ocean conditions in coastal regions, displacing local species, disrupting the completion of life-cycles dependent on present-day conditions, altering behavior patterns and predator-prey interactions. All of these factors could lead to significant shifts in ecosystem structure and function. Different ecosystems having different trophic pathways and dominant species may result.

Initial U.S. GLOBEC efforts are focused on understanding and quantifying present-day physical forcing and the effects of natural climate variability on the population dynamics of selected target species. Zooplankton, including meroplankton and ichthyoplankton, are a prime focus of U.S. GLOBEC because they are transported passively by ocean currents and are thus susceptible to changes in ocean circulation. Zooplankton are also a key link between phytoplankton and higher trophic levels (such as fish), thus climate-driven variations can affect ecosystem structure through trophic pathways. Wherever possible, U.S. GLOBEC scientists will undertake retrospective studies, including paleoclimate and paleoceanographic research, to characterize past natural variability over time scales of decades to centuries. In addition, such work provides the longer-term (interannual to interdecadal) context for shorter-term (order of 5-7 year) process-oriented research. An integral part of U.S. GLOBEC is the development of coupled physical-biological process models, resulting in assessments and predictions of the impact of climate change on marine resources and marine ecosystems.

## The Importance of the Populations within the CCS

### Economic Value

The California Current System (CCS) provides an excellent opportunity to accomplish U.S. GLOBEC goals in a region vital to U.S. interests. It is important to the regional and national economies due to commercial and recreational use by a large population and is cherished for its aesthetic as well as economic value (U.S. GLOBEC Report No. 7).

Collectively, the Eastern Boundary Current (EBC) systems in the Pacific and Atlantic account for approximately 35% of the global marine fish catch. Marine fisheries on the west coast of the U.S. produced a direct, indirect or induced impact of $4 billion on the economies of California, Washington and Oregon in 1992 (U.S. Dept. of Commerce, 1992; hereafter USDOC). Sportfishing and marine mammal watching yielded additional revenues. U.S. fishermen cannot now meet the demand for fish. As a nation, we exported $3.4 billion and imported $5.7 billion of fish in 1992. U.S. consumers bought 62% more fish this decade than two decades ago, 24% due to rising population and 38% due to increasing per capita consumption. The value of California seafood imports from other countries is eight times the value of its exports (Leet et al. 1992).

There are presently 40 stocks of living marine resources under management in the Pacific. Many of these stocks are fully or over-utilized; there are not sufficient data to evaluate the status of many others (USDOC). Commercially important fish in the CCS include the Pacific sardine, northern anchovy, Pacific mackerel, Pacific hake, salmon, rockfish, dover sole, sablefish and jack mackerel. There are also important recreational fisheries in all three west coast states. Significant invertebrate fisheries on the West Coast, include sea urchins, Dungeness crab and Pacific shrimp.

The long-term potential yield of fish stocks has traditionally been based on the assumptions that stock production in the recent decades of study are representative and that the essential climatic features that maintain stock production rates will stay the same. Reality often proves to be otherwise. One example is the sardine population in the CCS. Analysis of historical data now reveal that large-scale interdecadal climate change altered ocean conditions after 1945, which would have produced a natural decline in the sardine population even without fishing. This natural decrease was exacerbated, however, by uncontrolled fishing (Jacobsen and MacCall, in press). One of the prime goals of U.S. GLOBEC is to improve our understanding and ability to predict the vulnerability of living marine resources to natural and accelerated changes in the climate and to human pressures on those resources. This understanding should help to avoid prolonged decreases in populations of important species in the future.

### Ecological Importance

The strong connection between the CCS and basin-wide oceanic and atmospheric circulation provide linkages to global scale climate changes, as evidenced by its well-documented response to the basin-wide, interannual El Nino/Southern Oscillation (ENSO) variability. A similar response to interdecadal basin (or global) scale variability has recently been recognized. On both time scales, major changes in population abundances and distributions of key species have been documented in response to changes in the oceanic circulation and physical environment. Moreover, the applicability of results in the CCS to other EBCs gives the study global significance. For example, biological and physical responses to ENSO in the Pacific EBCs which have strong changes can be contrasted with Atlantic EBCs where ENSO effects are weak (Bakun and Parrish, 1980). Apart from differences in ENSO response, the atmospheric forcing, circulation and zooplankton communities and pelagic fish stocks of the California Current System are similar to other eastern boundary currents of the world ocean: the Humboldt Current (Peru/Chile), Benguela Current (Southwest Africa), and the Canary Current (the Iberian Peninsula to Northwest Africa). These systems often have narrow shelves and are characterized by coastal upwelling, equatorward flow over a poleward undercurrent and a small number of species of dominant pelagic fishes (anchovy, sardine, hake, mackeral and bonito). Fluctuations and redistributions of anchovies, sardines and pilchards occur in all EBCs.

U.S. GLOBEC research on the northeast Pacific boundary currents can utilize a rich history of time-series, quantitative surveys of zooplankton and fish off British Columbia, Washington, Oregon, California and Baja California Mexico and coastal process-oriented surveys. These can be used to define better the relation between zooplankton production and regional-scale processes like transport and local-scale processes like predation, upwelling and isopycnal shoaling. We also need seasonal and regional comparisons of the impact of pico- and large phytoplankton production on zooplankton populations, since the productivity of the bacterio- and phytoplankton is transferred to the higher trophic stages via zooplankton. While upwelling of nutrient-rich water stimulates primary and secondary production, it also may transport zooplankton, and fish and benthos larvae, out of their habitat or destroy the local aggregations of food on which they depend. Determining the relative importance of advective losses versus predation as dominant sources of mortality for planktonic populations is crucial. This issue, fundamental to population dynamic studies, has not been properly resolved for any marine planktonic population.

The impact of climatic change on zooplankton production depends on its persistenceŃshort-term changes in the environment, such as occur during an El Nino, may not impact the production of fish having generation times of five years or longer. It is important that U.S. GLOBEC relate physical oceanographic features to the production of zooplankton on which sustained resource productivity depends. While the adult stages of the zooplankton are well known, most resource species rely on their immature stages for food. The genetics and population dynamics of the critical zooplankton species are not sufficiently well known to link physical oceanographic events and trends to secondary and fishery production dynamics.

Existing long-term data series, such as the CalCOFI dataset, and the paleoecological data from sediments, are valuable for examining ecosystem response to past climate variability. The longer data sets allow the identification of natural modes of variability, prior to any anthropogenic modification (e.g., fishing). This temporal variability, as well as the large degree of spatial variability within the present system, can be used to identify and examine the mechanisms by which the CCS responds to changes in forcing, which can then be applied to predict biological responses to scenarios of future climate change.

## Program Elements

From discussions that began at a workshop in Bodega Bay in September 1991, four classes of studies (Program Elements), spanning different temporal and spatial scales, were identified that are needed to understand the mechanisms causing variability of CCS populations:

1. Modeling studies (addressing all scales)
2. Retrospective and comparative studies (seasonal-to-interdecadal scales)
3. Field process studies to include:
   - large-scale studies, focusing on latitudinal gradients, and
   - mesoscale studies, focusing on filaments, jets and eddies,
4. Long-term environmental monitoring

Modeling. The development, validation and improvement of biophysical ecosystem models will be conducted throughout the duration of the U.S. GLOBEC CCS program and forms its ongoing integrative element. Several types of models will be developed that integrate effects of important biological and physical processes affecting coastal populations. Biological subcomponents will be included in existing numerical circulation models, which will allow interaction of the biological and physical components. High resolution biophysical models will be constructed with more realistic representation of turbulence and fine structure in the vertical dimension. Population models will also be developed, which relate abundance and persistence of populations to varying physical and biological conditions.

Modeling studies will ultimately be used to test various climate change scenarios proposed in this Science Plan. This will mostly be accomplished by running the models in "stand alone" process-study experiments. By the end of the project, however, it is hoped that the models will be capable of being imbedded within coupled ocean-atmosphere GCMs, at least in a rudimentary fashion. This will allow a more complete test of the ability of the models to hindcast the statistical properties of past climate and ecosystem variability and the probable effects of increased concentrations of greenhouse gasses in the future. To do this, there is a need for further research into the methods of imbedding fine resolution models within basin-wide or global models and in assimilating both biological and physical data, to correct for poorly known initial conditions.

Retrospective and Comparative Analysis. The goal of this component is to define and understand the characteristic modes of natural variability over seasonal to centennial time scales in both the CCS and other EBCs. This goal will be achieved through assembly, analysis and interpretation of retrospective time series for the CCS and analysis of existing contemporary data sets from other EBCs such as the Peru-Chile and Benguela systems. Integration of paleoecological information with the historical CalCOFI and other plankton data sets is a critical element in the goal to link the information developed from U.S. GLOBEC field studies to natural climate variability at longer time scales. Moreover, using retrospective analysis in a comparative mode, we can compare life history strategies of species whose range spans several regions of the CCS, or of a species complex which occurs in several EBCs.

A compelling reason for selecting the CCS for study is that extensive historical and paleoecological data sets exist which permit determination of the natural modes of variability at seasonal and longer time scales. Analysis of physical, zooplankton and fisheries data will permit a description of CCS dynamics during past ENSO cycles, and elucidate changes that occurred during the 1976-1977 "interdecadal-scale" shift from cool to warm phases. Analysis of paleoceanographic data may permit study of regime shifts back in time for the past two millenia. In the future, when (or if) the system switches back to the cool phase, as determined from the long-term monitoring program, the present process studies will serve as a comparison for future process studies in the CCS.

Large Scale and Mesoscale Process Studies. The California Current can be divided into four regions, with each separated by a more-or-less distinct physical and/or biological boundary. From north to south they are: Region I (North of 43 deg N) extends from the southern British Columbia south to the vicinity of Cape Blanco, OR-Cape Mendocino, CA; Region II (35 deg N to 43 deg N) includes northern and central California, from Cape Mendocino to Point Conception; Region III (30 deg N to 35 deg N) is the Southern California Bight south to Punta Baja, Mexico and regions offshore; and Region IV (south of 30 deg N to 23 deg N), is Baja California from Punta Baja to Cabo San Lucas.

Mesoscale dynamics are interesting because they dominate much of the physical and biological dynamics of the CCS and because they differ in each of these regions as a result of regional differences in wind stress, intensity of coastal upwelling, coastal morphology, shape of the coastline, freshwater inflow, and the influence of advection, turbulence and buoyancy. There are also regional differences in planktonic, benthic and fish assemblages, the timing of plankton production cycles, and the reproductive activity of fishes. Since climate-controlled changes in large scale atmospheric and oceanic forcing have a major impact on mesoscale activity, a field research effort focused on this spatial scale is critical. Thus, regional differences in physical-biological linkages provide a natural laboratory for comparing potential changes in marine populations due to climate variability and climate change.

Monitoring and Observations. U.S. GLOBEC intends to augment existing monitoring programs and to initiate new programs as funding levels permit. A long-term environmental monitoring system should be designed to provide greater temporal resolution of ecosystem response to natural event-scale and seasonal variability, interannual variability due to ENSO, and long term climate variations. Monitoring is also intended to provide the long-term context for the short-term process-studies; regions/locations monitored will be selected to coincide with locations of mesoscale process studies and, if possible, long records of historical data. To the exent possible, monitoring of environmental variables will include real-time reporting of the data, allowing rapid response to unusual events.

## Time and Space Scales

Research within these four program elements will address two ranges of time scales, seasonal-to-interannual and decadal-to-centenial, and two space scales, mesoscale and large-scale. The central questions are articulated in the box below in terms of these scales. Below, we discuss temporal scales.

Seasonal-to-Interannual Variability. Longer term climatic changes in a region often consist of the effects of changes in the nature of the seasonal and interannual variability. Seasonal variability may be defined by even shorter events, such as the relatively rapid transition to upwelling conditions over much of the California Current in spring, or a sequence of events, such as the strength and frequency of winter storms. Interannual variability may, in turn, consist of changes in the timing of these seasonal transitions or in the accumulated effects of these sequences. Thus, although U.S. GLOBEC is primarily interested in the effects of longer-term climatic changes, the biophysical mechanisms responsible for those changes occur initially at the event scale. Within the CCS, the interannual physical and biological variability with the most severe economic and ecological effect is associated with the ENSO cycle. During the 1982-83 event, fish catch per unit effort off California was reduced by 30% and the overall loss to North American fisherman was estimated at $200 million. Much of our understanding of the response of marine organisms to ENSO is either anecdotal or so qualitative that it has little value for prediction. Because ENSO is one of the best documented and well-understood modes of climate variability, examination of the physical and biological response at this time scale is singled out for careful study. In addition, interaction of the ENSO time scale with the decadal (and regime shift) time scale will be given some emphasis. The program described previously-consisting of (1) monitoring of physical variables, plankton and nearshore organisms along selected transects and at coastal sites within the CCS; (2) development of coupled regional physical-biological diagnostic models to study physical and ecosystem response to ENSO forcing; and (3) process work on vital rates, such as reproduction, growth and mortality, or key populations-is well suited to address the ENSO time scale.

Decadal-to-Centennial Variability. At longer time scales, time series of sea surface temperature (SST) near the coast display distinct multidecadal periods of relatively cool and warm conditions, punctuated by the ENSO warm events (Miller et al. 1994a). SST observations at high latitudes have a periodicity of about 20-30 years which seems to be linked to atmospheric pressure anomalies; analysis of sediment cores from anoxic basins reveal a 60-70 year cycle in the relative dominance of sardine and anchovy over the last 1500 years. The direct observational time series, extending back 50-100 years, resolve one cycle of this pattern in the physical environment and ecosystem structure, with warming around 1925, cooling around 1948, and warming again around 1977. Coincident with the warming surface ocean temperatures in the mid-1970's is a notable decrease of zooplankton biomass in Region III and an increase in the sardine population in Southern California. The strength of springtime northerly winds diminished during this period and there is evidence that the large-scale ocean-atmosphere circulation changed.

From these observed changes, it is reasonable to assume that interdecadal fluctuations in ocean climate create changes in habitat that tend to favor certain species over others. Through retrospective analysis, descriptions of the system under different conditions in the past will be produced by making use of (1) the CalCOFI data base to compare cool regime conditions before 1977 with warm regime conditions after 1976, and (2) paleoceanographic data on fish scale and other biological debris in cores from anoxic basins to study the frequency of these shifts during the past 2000 years. The monitoring system put in place over the course of this 7-8 year program will continue into the future and provide continuity between the past and present observations and those made in the future, possibly within different phases of interdecadal cycles.

## Recommendations for Initial Activities

In this science plan we emphasize the broad questions which need to be answered and the hypotheses which need to be tested in order to increase our understanding of how the distribution and abundance of animal populations in the CCS is affected by past and present climate variability and how ecosystem structure may be altered by global warming and global climate change. The CENTRAL QUESTIONS AND GOALS are discussed in Section V in the context of the time and space scales of interest. The program elements, summarized above, are discussed in Section VI, POTENTIAL COMPONENTS OF A CCS STUDY. Clearly, the entire large, four-dimensional California Current, with its many habitats and species, cannot be sampled with sufficient resolution to determine its internal response to physical forcing at many points in time and space. The challenge is to design a program that takes advantage of the existing spatial and temporal variability to isolate the mechanisms likely responsible for determining the fates of populations within a climatically-changing ecosystem.

This Science Plan will form the basis for several Announcements of Opportunity (AO) for research on relationships between climate variability, physical and ecosystem dynamics, and climate change in the California Current. The first AO is expected to be released in the fall of 1994, and will call for proposals on some or all of the following activities, depending upon the level of funding available.

1. Modeling activities.
2. Retrospective data analysis and comparative EBC studies.
3. Augmentation to existing and initiation of new monitoring programs.

These efforts are discussed more fully in Section VII.