STATEMENT OF
DR. STEPHEN
MURAWSKI
DIRECTOR, OFFICE
OF SCIENCE AND TECHNOLOGY
NATIONAL MARINE
FISHERIES SERVICE
NATIONAL OCEANIC
AND ATMOSPHERIC ADMINISTRATION
DEPARTMENT OF
COMMERCE
BEFORE THE
SUBCOMMITTEE ON
FISHERIES AND OCEANS
COMMITTEE ON
RESOURCES
UNITED STATES
HOUSE OF REPRESENTATIVES
STRUCTURE AND
FUNCTION OF MARINE ECOSYSTEMS
JUNE 8, 2005
Mr. Chairman and members of the Committee, thank you for
inviting me to speak about the structure and function of marine
ecosystems. I am Dr. Steve Murawski,
Director of the Office of Science and Technology in the National Oceanic and
Atmospheric Administrations’ National Marine Fisheries Service (NMFS).
At the request of the
Committee, NMFS has provided a PowerPoint presentation on the structure and
function of marine ecosystems and the human interactions with these systems. This
testimony will serve as talking points for the attached slides.
This testimony
provides a brief overview of marine ecosystem science, including the various
types of science needed to support decision making when developing policies for
the marine environment. The challenges
of integrating ecosystem knowledge arise from the fact that many complex and
simultaneous processes are ongoing in the marine environment, and human uses
affect these systems in many ways. An
ecosystem approach to examining marine systems implies that we can examine
processes at varying scales of complexity and aggregation (for example,
multiple species and their roles in the environment) to understand the
essential details of their interactions.
The key processes of marine ecosystems are to capture solar energy and
transfer that energy among various groups of animals and plants. This energy production then supports
virtually all life in the oceans, and on land as well. Understanding these connections is essential
to valuing the full range of goods and services supplied by marine ecosystems. Although marine ecosystem science
(incorporating the physical sciences, biology, and social sciences) is still
relatively young, significant progress has been made in theory, observation,
and experimentation. I will summarize a
few areas of marine ecosystem science that are relatively well known, some
important questions that remain unanswered, and some issues that are
essentially unknowable (the topic of a recent workshop at Scripps Institution
of Oceanography).
As this map of the
Marine ecosystems can
be defined on many spatial scales, ranging from the entire marine environment
of the earth to a small bay or estuary.
The defining characteristics of an ecosystem apply no matter how the
ecosystem of interest is defined. Marine
ecosystems are defined by their geography, the animals and plants within that
geographical scope (including humans), as well as aspects of the physical,
chemical, and biological environment and the processes that control ecosystem
dynamics.
The environment of
the ecosystem includes the biological, chemical, physical, and social
conditions that influence organisms, and the environment is usually described
in terms of the aspects (physical, chemical, and biological) important to a
process under discussion.
Many of the important
physical and biological processes in the marine environment (such as sea
surface temperature, illustrated in the top panel of this slide, as monitored
by satellite), show gradual changes over large spatial scales. Likewise, while some animals and plants live
their entire lives in a very localized area (a few square kilometers), others, including
the great whales and migratory fishes such as tunas, use entire ocean
basins. How then do we define spatial
boundaries in the marine ecosystem to study processes and make decisions at a
regional level? These varying spatial
scales must be considered, particularly when we consider the interactions
between the physical environment and biological processes, including variations
in the climate system and its effects on biota.
One useful concept is to look at the world’s oceans at an intermediate
scale known as Large Marine Ecosystems, or LMEs. Several studies have defined about 45 LMEs in
the world’s oceans, with eight of these occurring in
The marine food
chain, or “web,” has at its base the production by marine plants of
phytoplankton. At successive trophic
levels (1 = phytoplankton, 2 = zooplankton, etc.), the amount of mass that can
be supported is only about 10 percent of the mass at the lower adjacent
level. This is because considerable
amounts of energy are required for growth, movement, and reproduction. Nutrients released by these processes are
recycled by the ecosystem back to the base of the food chain. Human activities influencing the marine food
web include increasing nutrients in the coastal systems, which may stimulate
phytoplankton production (which may have a variety of consequences for
ecosystems). Harvesting at the top
levels of the pyramid may also alter the number of animals in lower levels,
resulting in changes in the availability of species for human uses, as well as
in the dynamics of the ecosystem.
This graphic is a
composite satellite image of “ocean color,” which is an indication of
photosynthesis. Marine phytoplankton
(composed primarily of diatoms and dinoflagellates) are responsible for
photosynthesis in the ocean, the base of the marine food web. The requirements for photosynthesis are
sunlight and nutrients, such as nitrogen and phosphorus, as well as trace
amounts of other elements, including iron.
All photosynthesis occurs in the upper 200 meters of the ocean, and
mostly in the upper 50 meters, because of the inability of sunlight to
penetrate the depths. The “photic zone”
(less than 200 meters) represents only about 7 percent of the volume of the
oceans, whose average depth is about 2.3 miles.
Unused phytoplankton eventually dies and sinks through the photic zone,
so most nutrients in the ocean occur deeper than photosynthesis can occur. Therefore, to support the living system
nutrients must be transported from ocean depths to the photic zone. This occurs in upwelling zones and by other
current systems. Upwelling zones, such
as those off the west coasts of the
To understand how
various species and their physical and chemical environments interact, we must
make a variety of observations. Sea
surface observations of ocean color reveal complex eddies and “hot spots” of
productivity resulting from the interaction of marine currents, the geology of
the sea floor, and nutrient concentrations.
Various other species are influenced by these local differences in
marine production, which affect their abundance and distribution. Compared to observing sea surface color and
temperature, it is much more difficult to sample the three-dimensional
structure of the physical environment, as well as various species, including
mobile animals and those attached to the bottom (the “benthos”). Various sampling methods are applied by many
organizations to provide an integrated picture of variations in marine
ecosystems.
Long-term variations
in climate phenomena, such as the North Atlantic Oscillation (NAO), can result
in marine conditions that in turn affect the biological components of
ecosystems. A parallel Pacific Decadal
Oscillation (PDO) has similar impacts on biota of the North Pacific. The NAO results from variations between a
high-pressure system off the Azores and a persistent low-pressure system south
of
The NAO index is
based on the activity of the NAO system—a positive index means cooler and
wetter conditions in
Ecosystems are
influenced not only by variations in the world and regional climate, but by a
variety of human activities as well.
Most importantly, these human activities include nutrient enrichment of
coastal areas (such as
This graphic
illustrates the status of knowledge of species and processes affecting marine
ecosystems. Some facts concerning marine
ecosystems are well understood, some issues are currently unknown, and other
areas are essentially unknowable. We now
have a significant understanding of the surface dynamics and production of
phytoplankton, based on sampling with instruments such as satellites. Likewise, we have a considerable body of
knowledge regarding some major species of animals, including primary fishery
targets as well as important animals such as marine mammals and other
species. Our knowledge of 3-D dynamics
of ocean systems is good for selected areas, and we have mapped some of the
ocean habitats well. Less understood are
the number of species currently in the ocean and the effects of climate
variation on ecosystem dynamics. Also
less understood are issues such as the reversibility of human impacts on
species and ecosystems, and the appropriate valuation of the full range of
ecosystem goods and services. Some
issues are either very costly to investigate (e.g., complete mapping of the
entire sea floor), or conceptually difficult to resolve (such as predictive
models of many-species dynamics). Still
other issues may never be fully known, such as the structure and functioning of
“pristine” ecosystems (e.g., before human impacts).
This concludes my presentation, Mr. Chairman. I will be happy to respond to any questions that you or members of the Subcommittee may have.