Distributional Patterns and Sampling Problems

Chairperson: 	Richard Harbison
Rapporteur:	Loren Haury

ISSUES:

CONCLUSIONS:

Text of Chair/Rapporteur's Report:

Given limitations in our present knowledge of open ocean systems and how to identify "key" species in them, the GLOBEC objective was redefined in community terms:

To understand the underlying physical and biological processes that control the dynamics of key communities of marine animals in space and time.
Including studies of blue-water communities as part of GLOBEC will make programmatic conclusions more global and robust because the major ocean basins are the largest habitats on Earth. They are characterized by different biological and physical regimes which may respond differently, perhaps oppositely, to changes in global climate.

Identification of Target Species

Knowledge of community structure must begin with information on species compositional abundance, biomass, functional groups, and size distributions. Biological and physical factors will confound the interpretation of climatic effects on the diverse and poorly-studied species of the open oceans. Since the fauna of the open ocean is so diverse, selection of a few key species is precluded. Therefore, we use the term "target species", which has the additional advantage of not being semantically loaded. Investigations need to focus on a few target species whose distributions and basic biologies are reasonably well known. The target species will serve as a focus for research efforts. In order to understand their place in the open ocean ecosystem, other species that interact with them will also need to be studied. The process of identifying potential target species for study should begin early with literature surveys and preliminary studies focused on the following selection criteria:

While modest funding of a literature search would be useful for acquiring historical information, including previous results of a time-series nature, distributional studies and life history data, the work must also include pilot studies, ideally with international cooperation, in the major ocean basins. Most previous work in the open ocean has not collected critical information about the physical environment or species biology (smaller size classes, life stages) with modern collecting techniques. Preliminary work also needs to be done on culturing organisms and establishing methods to obtain rate estimates and other needed information to understand the dynamics of populations.

Methodology

Methodological constraints, particularly the need for easy, quantitative sampling, set limits to the kinds of animal populations that could be studied in the open ocean ecosystems. There was some discussion on the desirability of including commercially-important, open-ocean fishes, such as tuna, in the effort. However, the technical problems of sampling the various life history stages of large, long-lived, migratory stocks over meaningful temporal and spatial scales are daunting. The sampling gear of choice for U.S. GLOBEC open ocean studies would most likely be instrumented zooplankton nets (e.g., MOCNESS design), fished obliquely in the mid- to upper water-column. This would presumably constrain the potential target species to robust forms (e.g., crustaceans, squids, fish and salps as opposed to more delicate gelatinous forms) within the size range that can be reasonably collected with such systems (e.g., smallest developmental stage not less than 50 Ám and upper size limited by ability to avoid net capture). Pilot studies should use other strategies and technologies -- ROVs, submersibles, moorings, acoustics, video -- to establish the effectiveness of sampling the populations of interest and to determine large-scale horizontal and vertical patterns in species and biomass distributions. Further, target species cannot be studied in isolation; one must know their predators, prey, competitors, symbionts and parasites as well. Therefore, a variety of sampling methods will be required, since no single method of sampling can provide biologically meaningful qualitative and quantitative information over a range of spatial and temporal scales (Harbison, 1983).

Problems

Several concerns provoked considerable discussion in this working group and probably warrant even further consideration. First, it was not entirely clear what is meant by "open ocean" and "blue water" environments, how they differ from one another, and where their boundaries stand with respect to the ocean margins. While the group tended to focus on the subtropical gyres as the likely locations of a "blue water" research effort, they are clearly only part of the open ocean, most of which is poorly studied and some of which may be more relevant for global change investigations. Even so, it was difficult to cleanly distinguish the blue water fraction of the oceans from all others by species, spatial and temporal patterns of variability in biology and physics, stratification, or light. Second, we wondered about problems associated with following the life histories of populations in advective environments, particularly the interplay between vertical structure in currents and migratory behaviors. It is not inherently clear that advective problems are less severe in the open ocean. Lastly, we considered whether studies of blue-water populations ought to be focused on the cores of ocean gyres, where advective problems may be minimal and there is a greater likelihood of populations approximating stable age distributions (a great advantage in determining life tables in population dynamic studies). The alternative, or complementary, approach would be to study the "edges" of ocean regions, where the dynamics of species are more temporally and spatially variable, but where the "signals" from climatic changes may be more clear.

Opportunities

Certain advantages (logistics and basic measurements of lower trophic levels) link GLOBEC blue-water studies to JGOFS time-series stations in the North Pacific (HOTS) and North Atlantic (BATS) subtropical gyres, In addition, WOCE lines and CPR tracks provide opportunities for more spatially extensive sampling schemes.


homepage contents previous newsletter next newsletter