Workshop Structure and Summary

Workshop Structure

The workshop began with background briefings on U.S. GLOBEC planning and research activities, and an introduction to the PICES Climate Change and Carrying Capacity Science Plan. Participants were then divided into six multiŠdisciplinary breakout groups. These six breakout topics covered issues that were relevant to the development of a research plan designed to address the impact of climate variability on biological systems: climate change, regime shifts, carrying capacity, modeling, technology, spatial and temporal scales. The following day, participants were divided into groups to discuss specific recommendations for future research in three geographic regions: Gulf of Alaska, oceanic subarctic, and the Bering Sea. The following summaries provide a synopsis of the discussions and recommendations made in each of the breakout sessions. More detailed accounts of group discussions are found in the breakout session chapters.

Breakout Session 1. Climate Change: What are the likely scenarios for climate change in the North Pacific and how would they influence the ecosystem?

This breakout session was devoted to discussion of the potential impact of climate change possibly caused by increased CO2 and other greenhouse gases from anthropogenic sources. Climate change would influence North Pacific ecosystems primarily through four physical factors: mixed layer depth (MLD), volume and location of marine habitat, sea ice, and river outflows. MLD is strongly correlated with biological productivity over the entire North Pacific, but the response of MLD to climate change is liable to be different in the three main regions. Changes in marine habitat, thus the zoogeographic distribution of marine species, are expected to accompany ocean warming, with particular impacts on species at the edge of their ranges. Sea ice is foreseen to decrease both in space and seasonal duration, with effects on the Bering Sea's primary productivity and distribution of many marine fish, sea birds and mammals. The overall magnitude and seasonal cycle of river flows may change significantly, with implications for coastal currents and freshwater habitats for salmon.

Breakout Session 2. Regime shifts and decadal shifts: can they be detected, what is their impact, are they predictable?

There is compelling evidence of interdecadal changes in the physical environment of the North Pacific and Bering Sea. The most recent shift occurred in the late 1970's. These changes appear to be linked to large scale shifts in atmospheric processes. Marine organisms seem to respond to these decadal scale changes in the physical environment. The group acknowledged that additional research is required to improve our understanding of the mechanisms underlying the response of marine organisms to shifts in physical conditions. North Pacific basin modeling shows promise in simulating and explaining decadal fluctuations of the ocean over coarse scales. Regional and mesoscale oceanographic models exist for the Gulf of Alaska and need to be developed for other regions. Several physical and biological variables were identified that could be used as diagnostic indicators of regime shifts.

Breakout Session 3: What is carrying capacity?

This breakout group discussed the concept of carrying capacity and methods to measure carrying capacity. The group adopted the following definition of carrying capacity:

Carrying capacity is a measure of the biomass of a population that can be supported by the ecosystem. The carrying capacity changes over time with the abundance of predators and supply of food. The food supply is a function of the productivity of the prey populations and competition for that food from other predators. Changes in the biotic environment affect the distributions and productivity of all populations involved.
The group discussed several indices of carrying capacity that could be used to assess relative changes in the status of a population. The group noted that size spectrum theory, which relates rates of productivity to the size class of organisms in the ecosystem, is a potentially valuable conceptual framework for examining carrying capacity questions. Measurements of climate change effects on the carrying capacity might be examined using fishing experiments to examine the impact of the removal or exclusion of a particular component of the ecosystem.

Breakout Session 4: What is required to model the impact of climate change on the carrying capacity of the region?

Participants discussed a variety of modeling approaches and suggested that different types of models could be beneficially nested: spatially, temporally and trophically. Many physical models of the North Pacific and Bering Sea already exist and could be utilized in the U.S. GLOBEC program. While the formulation of governing equations and choice of parameters for bioŠphysical models is difficult, reasonable choices can be made. Encouraging results have been obtained from the application of coupled bioŠphysical models in other areas of the world (such as the North Atlantic).

Breakout Session 5: What are the technological impediments to measuring the effects of climate change on the carrying capacity?

This group recognized that climate change by definition is a large scale, long term process and will require ample measurements collected over a large geographical area for a long duration. They recognized that a successful program will require that study sites are selected at key or pulse points where the variance is minimized and the effects of climate change on carrying capacity are indicative of large scale change. A variety of technical issues were discussed and the disadvantages and advantages of each were identified. The group encouraged efforts to measure sea-surface salinity from satellites to map the large-scale distribution of this variable which is dynamically more important than temperature in the Gulf of Alaska and Bering Sea due to large freshwater inputs. They also noted that deep ocean currents could be monitored using electromagnetic observations from submarine telephone cables and identified the Kamchatka Current and Alaskan Stream as pulse points. Finally they noted the need for research on noncommercial species such as jellyfish or forage fish. These species may play a critical role in determining the carrying capacity of oceanic systems.

Breakout Session 6: What are the spatial and temporal scales required to resolve questions concerning climate change and the carrying capacity?

This group concluded that the spatial scale of climate forcing is large, basin scale at least. The group noted that while considerable attention has been devoted to interannual variations, decadal and longer time scales may be more important for resolving issues of climate forcing and its impact on marine ecosystems. Participants acknowledged that the response time to climate change differs between species. Criteria for selecting specific time and space scales for a future U.S. GLOBEC study must include: 1) concentration of important variability, 2) relationship to plausible mechanisms of interaction, 3) relationship to applied problems.

Coastal Gulf of Alaska Breakout Session

Participants in this Breakout Session were asked to define a subset of research questions that should be investigated to advance our understanding of the impact of climate change on: physical forcing, lower trophic level species, and higher trophic level species. Forcing questions focused on four forcing factors: atmospheric forcing, interactions between the Alaska Stream and Alaska Coastal Currents, the influence of bottom topography on coastal circulation, and tidal influence on nutrient flux. These four large scale factors influence important physical processes such as: mixed layer depth, mixed layer temperature, retention times (eddies), turbidity, and cross shelf transport. Research to describe the functional relationship between large scale forcing and local conditions will be required. Lower trophic level questions focused on five research topics including: transport influences on the composition and production of plankton communities, the role of grazing and predation on the structure of plankton communities, trophic phasing, climate change effects on over wintering plankton communities, and freshwater influences on plankton communities. Several potential research topics relevant to higher trophic level species were discussed including efforts to identify climate change effects : a) the spatial distribution of predators, b) prey abundance, c) species composition of fish communities, and d) seasonality of resources to apex consumers.

Research activities that might be undertaken to answer these questions included retrospective studies, monitoring studies, process oriented research and modeling. In the Gulf of Alaska many physical and biological datasets exist that could be used for retrospective analyses. Likewise, many potentially valuable monitoring platforms in the Gulf of Alaska were identified. Bio-physical models have been developed for British Columbia, Prince William Sound and Shelikof Strait. Efforts to nest regional models of Shelikof Strait (NOAA's FOCI program), Prince William Sound (Exxon Valdez Oil Spill Trustees, SEA program), and Southeast Alaska (APRISE, Canada's La Perouse program) into a large-scale bioŠphysical model of the Gulf was recommended. A broad-scale biological model of the Gulf might include the following: phytoplankton and protozoa, euphausiids and copepods, jellyfish, salmon, herring, and pollock.

Oceanic Subarctic Breakout Session

This breakout group divided into three subgroups to discuss projects relevant to 1) physical forcing/lower trophic level response, 2) higher trophic level response, and 3) ecosystem interactions. The first group identified three projects for future study: a program to document changes in standing stocks of plankton, a project to distinguish the effects of iron, Ekman pumping, cloud variation, and other factors on primary production, and a test of the Chelton hypothesis on the split of the west wind drift as it nears North America. Five questions were identified for future research of higher trophic level responses. These questions focused on mechanisms responsible for sustained high biomass of higher trophic level species since 1976-77, identifying historical biomass levels, studies to examine the coherence between the eastern and western gyres, bioŠphysical interactions, and regulatory factors controlling the carrying capacity of salmon. The ecosystem sub-group identified four research topics: effects of Kuroshio/Oyashio currents on coastal ecosystems of Asia and the deflection of these currents into the eastern subarctic, effects of subarctic currents and ENSO events on the subarctic coastal ecosystem, effects of the transition zone on the subarctic ecosystem and the effect of deep water species on near surface ecosystems. Retrospective, monitoring studies, process oriented and modeling projects were identified to address each of the research topics.

Bering Sea Breakout Session

The Bering Sea breakout group began their discussions by acknowledging that Bering Sea is possibly the most productive of the northern high latitude seas. The group noted that a first order understanding of the Bering Sea has been obtained and that research programs should focus on studies aimed at elucidating the mechanisms linking environmental change to responses of the system. Four specific research topics were identified by the group:

  1. What is the relation of the range of storm activity to the annual production budget and food web dynamics of the mixed layer?

  2. What is the relation of the sea ice meltŠback bloom to total annual production?

  3. How does the nature of the spring bloom determine the partition of energy between the pelagic and benthic ecosystem components?

  4. Will climate change alter habitat/domain volumes and how will this influence recruitment?
Retrospective, modeling, process oriented studies and monitoring activities designed to answer these four questions were identified.