Open Ocean Issues Discussed at Workshop

The purpose of the workshop was to discuss potential effects of global climate change on the species diversity, biomass, and community structure of open ocean pelagic environments. There are several reasons to consider GLOBEC questions in the open sea. First, is the issue of stability. If the apparent stability of oceanic communities is due to internal biological checks and balances, then this system might be more resistant to climate change than other more variable environments. However, if the stability of the ecosystem is due to the constancy of the physical environment, then blue water communities might be less resistant to climatic perturbation than coastal systems. Second, because of the sheer size of open ocean ecosystems--ca. 60% of the surface area of the Earth--climate-driven changes of population biology or community structure, could have profound influences on the biosphere. To determine whether open ocean and nearshore pelagic environments respond differently to potential climate change will require increased understanding of organismal and population responses to physical and biological forces. U.S. GLOBEC is planning studies of the coupling of biological response to physical forcing in several nearshore environments (Georges Bank, California Current). This workshop addressed similar issues, but in open ocean environments. Such effort is needed for two reasons: first, very little is known about the life histories or population ecologies of zooplankton and fishes of open ocean gyres, and second, it is probably invalid to extrapolate knowledge gained from coastal species to blue-water species.

Twenty-two participants from the U.S., Canada and France met in Woods Hole, MA for three days in September 1993 to discuss this topic and recommend research plans consistent with U.S.GLOBEC objectives. The first day was devoted to informal presentations on subjects ranging from plankton community structure to immunological methods for measuring growth rates. A goal of this discussion was to introduce new biochemical, molecular and genetic techniques that might be applicable to measurement of population dynamics and life history parameters of open ocean species that have previously been studied by more classical approaches. Following these talks, four working groups were formed: A) Population Characteristics and Genetics; B) Distributional Patterns and Sampling Problems; C) Biological Processes and Rates; and, D) Physical and Biological Forcing.

Group A considered some of the physical and biological factors that maintain species diversity and community structure in oceanic environments, and whether these forces led to comparable communities in the central Atlantic and Pacific. They discussed the genetic composition of oceanic species, raising questions about gene flow and homogeneity, and the existence of phenotypic sub-populations adapted to more local ecological conditions. The group recommended time-series studies of physical and biological changes at fixed sites, focusing on a small number of target species. They cautioned that the taxonomic and genetic identity of the target species must be unequivocal, and that new methods might be needed to ensure that this is the case. They also stressed the importance of understanding behaviors of the organisms.

Group B discussed questions of species distributions and sampling strategies. They began with consideration of how "open ocean" should be defined, and went on to compare the relative effects of changes in climate and circulation on communities in the centers of gyres versus the ocean margins. It was suggested that understanding the structure of open ocean plankton communities should begin with assessment of biomass distribution, then functional groups and finally species. Criteria were developed for selecting candidate species, or groups of species, which could be studied in multiple oceanic regions over long enough periods to seek evidence of the effects of climate change.

Group C was concerned with the biological processes that control population dynamics. They discussed possible differences in vital rates of oceanic versus neritic species, and the mechanisms by which climatic changes might act on those rates. There were questions raised about whether studies should focus on "typical" gyre environments, more productive margins, or other "hot spots". Problems of measuring biological rates of species dispersed in time and space were considered. This group recommended initial analyses of existing data on vital rates of oceanic versus nearshore species and efforts to develop new methods for measuring rate processes and sampling micro-scale distributions.

Group D debated the relative importance of physical versus biological forces in affecting population dynamics and community structure. They considered temperature and wind stress as two primary physical forces which might alter population biology via their effects on warming, stratification, advection, turbulence and circulation. Spatial and temporal distribution patterns brought about by these forces might be expected to constrain feeding, reproduction and dispersal of species. Principal biological factors acting on population dynamics were assumed to be food supply and predation, although the roles of disease and parasitism are not well understood. Understanding behavior of organisms relative to physical and biological forces was considered prerequisite to a study of possible climate change effects. This group recommended a re-sampling of the North Pacific gyre to compare community structure two decades later, and new, long time-series studies at other accessible oceanic sites.

The workshop participants recommended a staged implementation of an Open Ocean GLOBEC program, beginning with retrospective analysis and proceeding to pilot studies and larger scale field programs. Central to the plan is selection of a small number of target species that have stable circumglobal distributions in several oceanic gyres and are tractable for process and population studies. Known biological and genetic characteristics of these species could be accounted for, so that environmental effects in different regions could be clearly seen. Target species would become the focus of population dynamics research conducted as time-series and transects in several parts of the world ocean. These efforts would be allied with other large programs that could provide data on global climate conditions. (This synopsis of the U.S. GLOBEC Open Ocean Workshop was prepared from a draft report of the meeting, developed by Larry Madin and Mike Landry, who co-chaired the workshop in Woods Hole. A final report of the workshop discussions and recommendations will be published later by U.S. GLOBEC).

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