Distributional Patterns and Sampling Problems
Chairperson: Richard Harbison
Rapporteur: Loren Haury
- How do we define "open ocean"--by geography, hydrography or biology?
- Are climate signals and species responses likely to be stronger at the edges than in the middle of gyres?
- Is advection more important in the centers of the gyres or at the edges?
- In what order do we best gain information about community structure--biomass, functional groups or species?
- What sampling methods--nets, acoustics, ROVs, submersibles--are needed to investigate the biology of oceanic populations?
- Comparative studies should focus on a few "target species" for parallel studies in different regions.
- The selection of target species should be based on literature and pilot studies focusing on distributional patterns and experimental tractability. In particular, target species should include organisms with circumglobal distributions, congeners from different oceans, and different genera with similar functional roles.
- It is essential to quantify life history parameters and population dynamics of target species over time and space relative to variations in the physical environment.
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
To understand the underlying physical and biological processes that
control the dynamics of key communities of marine animals in space and
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.
- Species that are now believed to have circumglobal, cosmopolitan distributions.
- Closely related species in the same genera from different oceans.
- Species from different genera which appear to fill similar functional roles in different ocean systems.
- Closely related species that may be splitting environmental regions (to compare with globally distributed forms).
- Species that can be sampled quantitatively and relatively easily.
- Species with identifiable life history stages.
- Species that are abundant and present all, or most, of the time.
- Species that are tractable for experimental work.
- Species which exhibit various behaviors (e.g., vertical migration) which might be impacted by changes in the physical or biological environment.
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).
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
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.