EXECUTIVE SUMMARY
Rationale for a U.S. GLOBEC Field Program in the California Current System
It is no longer reasonable to assume that marine populations live in a stable environment. Both
paleo-oceanographic and contemporary data indicate strongly that the circulation and average physical
properties of the coupled atmosphere-ocean system change at time scales ranging from interannual to
millennial. Some of this variability is natural; some may be caused or amplified by human activities. In
either case, it is important to know how marine ecosystems will respond. GLOBEC (Global Ocean
Ecosystems Dynamics) is the component of the U.S. Global Change Research Initiative that will
address these issues.
Research sponsored by GLOBEC will have several shared approaches and themes (U.S. GLOBEC
Initial Science Plan, Peterson et al. 1991). The key elements include a close working partnership
between physicists and biologists, process-oriented emphasis on the linkages between physical and
biological components of the ecosystem, field programs combining observation with numerical
modeling, and advanced data collection technologies.
Eastern boundary current "upwelling" ecosystems have been identified as important study areas by
both national and international GLOBEC planning committees. To develop the next stage of GLOBEC
research on these systems, 54 participants of the U.S. GLOBEC workshop on eastern boundary
current ecosystems met from September 17 to 20, 1991, at the Bodega Marine Laboratory of the
University of California. The workshop was jointly sponsored by the National Oceanic and
Atmospheric Administration (NOAA) and the National Science Foundation (NSF). Its goals were to
identify and discuss key scientific issues associated with GLOBEC field research on eastern boundary
current ecosystems in general, and on the system bordering the west coast of North America (the
California Current) in particular.
Workshop Structure
The workshop began with background briefings on GLOBEC planning and research activities (by
U.S. GLOBEC steering committee and NSF representatives); an overview of recent and coming
physical oceanographic research in the California Current system, and the capabilities of and probable
time window for coming satellite missions (both by P.T. Strub); and recent and planned
NOAA/NMFS research programs (by P. Smith).
Participants then separated into nine multidisciplinary working groups. Most of these groups dealt
with a subset (often scale-dependent) of climate-population or biological-physical linkages believed to
be particularly important and appropriate for study in the California Current. Some of these linkages
had already been identified by the U. S . GLOBEC steering committee (e.g., transport and retention of
organisms by mesoscale hydrographic features; latitudinal gradients; seasonal and interannual time
scales). Others (e.g., the potential for abrupt change in composition and structure of biological
communities) were identified through discussions between the workshop cochairs and potential
workshop participants. An additional set of working groups dealt with the opportunities and
requirements of particular kinds of information (acoustic and optical sensors, biotechnology, and the
local paleo-oceanographic record). For each topic, working groups were asked to prepare a report
identifying key research questions, optimal species, study sites, tools, and observation periods. At the
end of each day, a plenary session reconvened for brief summaries of recommendations from each
working group.
Working Group Reports
The individual working group reports are summarized here and presented in detail in Section 3. The
final part of this Executive Summary is a brief discussion of some important additional or shared
themes that emerged in discussions within and between working groups.
1. Latitudinal Gradients Within the Eastern Boundary Current System
The California Current spans more than 20 degrees of latitude along the west coast of North America. Its
range exceeds the scales of dominant atmospheric pressure systems and of regional coastal
morphology. From north to south it can be divided into three major regions, each differing from the
others in wind stress, intensity of coastal upwelling, coastal morphology, freshwater inflow, and
influence of long-time-scale advection. The working group recommends that the overall field program
include a between-region intercomparison of physical forcing and biological response. The borders of
these regions appear to be zoogeographic boundaries for some species, population boundaries for
others. Still other species migrate through all three regions, but occur in each at different life stages.
As noted above, a variety of physical processes contribute to the regional differences. The existence of
latitudinal gradients provides a "natural experiment" on the relative importance and role of different
forcing functions in marine population dynamics. As well, the spatial gradients of the physical
processes are not fixed, but shift during the El Niño/Southern Oscillation, intrusions of subarctic
water, and other events. It is highly plausible that they would also shift under changing global climate,
but by no means certain that the shifts would be of uniform magnitude and direction.
2. Importance of Mesoscale Physical Features to Ecological Processes in the California Current System
Oceanographers have long known that the physical and biological characteristics of eastern boundary
current ecosystems vary intensely in space, but until very recently there have been no observational
tools for resolving the pattern of this variance. Satellite observations of surface temperature fields in
eastern boundary current systems have revealed a complex and energetic system of filaments, squirts,
and persistent eddies. Within the California Current system, these recurring mesoscale-to-subregional
flow features are most prominent off the central and northern California coast. Both satellite (ocean
color) and ship-based measurements show a strong spatial association between biological pattern and
these physical structures. But the causes for the biological pattern (i.e., the importance of a particular
class of physical feature for aggregation, growth, retention, and dispersion of a particular population
or trophic level) remain poorly known. A null hypothesis is that shared physical and biological
patterns result solely from shared advective history. The working group recommends research to test
this as well as a number of alternate hypotheses. The research should include comparisons of
population density, genetic composition, and demographic rates inside and outside major mesoscale
flow features; measurement of advective loss from or delivery to core habitat; study of the
intensification of environmental gradients by convergent secondary flow fields; and evaluation of the
effect of resulting sharp environmental gradients on organisms that move into the gradient region. A
number of technical needs were identified. Satellite observations and drifters are needed to direct
biological sampling. Biochemical techniques are needed to evaluate population structure and
demographic rates. Bioacoustic instrumentation is needed to resolve detailed spatial covariability of
biomass and size distribution.
3. Paleo-oceanographic and Long-Term Historic Evidence of Past Variability
Two major challenges of the GLOBEC program are the detection of the ecosystem's response to
global change, and the separation of anthropogenic effects from natural climatic variability. One of the
most powerful tools for resolving these issues is time series analysis. The California Current system
provides two exceptional and complementary sets of time series: the high-resolution paleosedimentary
record, and the California Cooperative Oceanic Fisheries Investigations (CalCOFI) data set and sample
archive. The working group recommends enhanced use and analysis of both. The anaerobic sediments
of the Santa Barbara Basin and other localities retain detailed annual chronologies from which the
dynamics of major fish populations, plankton, and climate variability can be reconstructed over
hundreds of years by using animal and plant remains and geochemical techniques. The CalCOFI data
document the behavior of the ecosystem over the last four decades and can be interrelated with the
sedimentary record. Both can be linked to known changes in climate and ocean circulation. Both can
also be used to evaluate the response of numerical models to simulated environmental change.
4. Nutrient Input Mechanisms in Eastern Boundary Current Regimes
Eastern boundary current ecosystems are among the most biologically productive. A range of physical
processes collectively cause relatively high levels of new nutrients at the sea surface. New nutrient
input and subsequent primary production (and the variability of these) can significantly affect upper
trophic level productivity and community structure. The working group recommends study of the
importance of 'bottom-up" control of eastern boundary current ecosystems in the following areas: role
in setting large-scale average productivity and carrying capacity; correlation of local input rate with
spatial and temporal variations in food quality; effects of food quantity and quality on consumer
community structure; sensitivity of energy transfers between trophic levels to physical variables such
as nutricline depth, upwelling rate and timing, and large-scale and mesoscale advective pattern.
5. El Niño/Southern Oscillation (ENSO) Effects Within the California Current System
El Niño represents an environmental extreme in the eastern boundary regions of the Pacific Ocean, and
is a dominant component of environmental variability at interannual scales. There have been 43
strong-to-very-strong El Niño events, and many weaker ones, in the five centuries since written
accounts of climate were first made in the Americas. Any study of eastern boundary currents of the
Pacific extending for a decade or longer should therefore expect to encounter an El Niño event. The
changes associated with El Niño conditions should not be interpreted as prototypes for the effects of
generalized global warming, and it is not yet clear to what extent ENSO frequency and intensity would
be affected by greenhouse warming. But at the least, El Niño represents an important additive
component of environmental variation, and it must be sampled to understand ecosystem response to
the expected range of environmental conditions. A well-developed and complete El Niño "contingency
plan" should be designed into all GLOBEC field programs to insure adequate coverage.
6. Special Tools
6.1 Technological Needs for Eastern Boundary Current Experiments
The working group strongly supports the recommendations of past U.S. GLOBEC reports on the
acoustical and optical needs (Holliday et al. l991) and biotechnology needs (Incze and Walsh 1991) of
GLOBEC field programs. The group stresses that developments proposed in these reports and
subsequently described in requests for proposals are vital to eastern boundary current programs as
well as to other GLOBEC field programs. A few new technological needs specific to eastern boundary
currents were identified, including biochemical techniques that can be applied to small amounts of
sediments and archived plankton collections, and special tools for collecting sediment samples.
Instrumentation needs not met by current development projects were also listed.
6.2 The Role of Models in the Study of Eastern Boundary Current Systems
A suite of eastern boundary current ecosystem models is needed to further our understanding of the
California Current ecosystem. The working group recommends that development and sensitivity
testing of such models begin immediately. For generality, the structure should allow alternate models
of component processes to be tested. Because of the complexity of the system, the biological
component of the model should include multiple trophic levels, each containing several taxonomic and
developmental-stage subdivisions. Other model components requiring considerable research and
development include the physical model, patch dynamics, migration patterns, and reproductive
patterns. The long-term goal is a set of models that reproduce the behavior of the natural system,
including the response to climate change. But the initial objective should be to understand the
dynamics of the system rather than to reproduce or predict detailed time series.
7. Linkage of Observation Programs at Different Time and Space Scales
Mechanistic understanding of individual physical-biological linkages within the California Current
system will require a number of intensive and relatively localized and independent process studies. To
understand the interrelationships among these processes and the ecosystem's overall response to
environmental change, it will be necessary to link these intensive studies. It will also be important to
sample oceanographic trends and events that occur outside the "intensive" observation window. The
working group made a number of recommendations to accomplish these goals. Intensive studies
should be undertaken for a total of 5-10 years; should include a basic suite of important taxa; and
should resolve cross-shore domains (coastal, shelf, and offshore) within each of the three major
alongshore regions identified by the working group discussing latitudinal gradients (section 3.1).
Less-detailed monitoring should be maintained for about 20 years; should provide near-real-time
output of basic data; and should be able to trigger opportunistic intensive studies of special conditions
whenever they occur. Both intensive and monitoring studies should be timed and designed to take
advantage of available satellite sensors. Data management and exchange protocols should be specified
in advance. Finally, numerical models spanning multiple levels of system organization (e.g.,
individual, population, community, ecosystem) should be used to identify particularly important areas
of information.
8. Major Shifts in Species Composition and Ecosystem Structure
Time series of physical and biological measurements in eastern boundary currents exhibit abrupt
changes in component variables; these changes seem unpredictable and inconsistent with those of the
preceding time period. Such qualitative shifts are obvious in long-term records of temperature and fish
abundance, and may also be related to abrupt gradients in within-time-period spatial distributions.
Most recently, a major shift occurred in the mid 1970s from a colder to warmer-than-average regime in
the California Current. This shift was accompanied by a drop in zooplankton abundance, vigorous
recovery of the depleted sardine population in the Southern California Bight, changes in salmon runs
in British Columbia, and many other changes. Despite the recognition that physical and biological
variables often exhibit nonstationary properties, this concept is overlooked in actual practice. For
example, resource managers typically use constant reference points such as steady-state carrying
capacity and equilibrium-unexploited abundance in their models. Steady-state assumptions are clearly
inappropriate even in the absence of anthropogenically forced climate change because qualitative shifts
are a normal property of eastern boundary ecosystems. Thus, the group hypothesizes that the
ecosystem response to global climate change may consist of abrupt changes in qualitative states - step
functions rather than gradual trends paralleling the increasing atmospheric concentration of greenhouse
gases. As part of the eastern boundary current GLOBEC program, the working group strongly
recommends research on qualitative shifts, including the physical-biological linkages causing and
maintaining shifts, the role of system nonlinearities, evaluation of sensitivity to initial conditions, and
prediction or early identification of abrupt change. Understanding the mechanism of long-term
qualitative change in eastern boundary current ecosystems will be a major intellectual challenge. Even
if prediction proves unfeasible, early recognition of qualitative shifts would be beneficial. Therefore, a
major goal of this proposed GLOBEC research is to develop a diagnostic capability that could be
implemented by a line agency such as NOAA.
Shared and Emergent Themes
Three concepts frequently recurred in working and planning sessions and deserve to be highlighted as
unifying themes for the entire workshop.
The first of these themes was a keen interest in abrupt changes in species composition as a
characteristic of eastern boundary current ecosystems and as a response to climate variability. For fish,
major qualitative shifts in the pelagic community have been documented by both historic catch data and
the paleosedimentary record. For plankton communities, major changes in composition have been
observed both in spatial structure and in multiyear time series. There are several reasons why
qualitative change is an important concern . The first is theoretical evidence that complex systems may
have multiple quasi-stable states. Each state, once established, may resist moderate levels of
perturbation, but once disrupted may be very slow (or even unlikely) to reestablish itself. A second
reason is that most resource management models assume gradual approach to global equilibrium and
are poorly equipped to predict or reverse rapid exogenous change. A third reason is that many
consumer species (including people) are highly specialized in their prey preference. A major qualitative
change at one trophic level may therefore transfer broadly through the ecosystem.
The second theme is a broad-brush but highly suggestive correspondence between the boundaries of
biological and physical domains. Although further research is needed, there is evidence for shared
boundaries in both large-scale and mesoscale spatial pattern, and in the distributions of planktonic,
nektonic, and benthic species. Despite the large latitudinal range of many species, the California
Current encompasses an extremely rich large-scale mosaic of life-history strategies. This is particularly
evident in the spatial and seasonal allocation of reproductive effort. There is also a mosaic of physical
forcing that is particularly pronounced for flow-field variables. This suggests a useful reinterpretation
of "endemic" distributions: instead of being adapted to the local scalar environment (e.g., a water
mass), species or populations may be primarily adapted to a prevailing local set of physical dynamics
(presence or absence of seasonal flow reversal, presence or absence of coastal buoyancy input,
seasonality and intensity of upwelling, seasonality and intensity of jets and eddies...). This can be
viewed as an extension of the "member-vagrant hypothesis" (Sinclair 1988). A key point is that core
habitat is defined by the intersection of a set of flow-field characteristics; the individual components of
this set may be affected very differently by changes in large-scale climate . Research should examine
the importance of different physical components, their potential for spatial and timing shifts, and the
plasticity of organisms' adaptive response.
A third shared theme was an emphasis on the flow-through character of eastern boundary current
systems. There is substantial spatial propagation and advective throughput of water properties,
physical features, and organisms. In consequence, research programs will usually need to look
"upstream" for causes and precursors of local conditions; thus they will need to cover large areas.
In addition to the three shared concepts, a consensus existed on three methodological issues or
approaches. First, a consensus existed on the taxa that would be the primary focus of the program.
These include euphausiids, copepods, and thaliaceans among the zooplankton; hake, anchovy, and
sardine among the finfish; and crab, barnacles, and urchins among the meroplanktonic benthos. These
groups account for much of the total animal biomass in the various domains of the system, and include
a broad range of life strategies. However, the list is not intended to be restrictive; there will be many
questions for which other or additional taxa should be studied.
Secondly, there was agreement on the need for satellite oceanography to provide a spatially detailed
overview of the California Current. The measurements of particular interest are temperature, ocean
color, and sea-surface elevation. Based on present mission schedules, satellite coverage of the system
will be optimal for a period of about five years in the mid to late 1990s. This provides a strong
incentive to begin the intensive field program soon.
Thirdly, there was general agreement that the program should take advantage of the unique time series
data provided by the analysis of the sedimentary record of anaerobic basins, and CalCOFI and other
archived data and samples. Such studies could provide the needed temporal linkages between
proposed short-term site-intensive studies and the longer-term dynamics associated with climate
change.