Status, trends and the future of the marine pelagic ecosystem

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Alfred-Wegener Institute for Polar and Marine Research

2003

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SUMMARY

Globally, humans impact environments and ecosystems faster than they become aware of their

effects.

The marine pelagic ecosystem includes a tremendously large and diverse environment, which might

accordingly be considered to be resilient to externally forced changes, whether from humans or

climate.

This review considers that general hypothesis by pursuing two objectives. The first is to document

the current status of and recent anthropogenic impacts on the marine pelagic ecosystem, with

emphasis on the epipelagic zone (0–200 m) where organisms are concentrated and human impacts

have been greatest. It shows that humans have proven capable of assuming the role of top

carnivore in pelagic ecosystems where living resources are attractive and financially amenable to

exploitation, and that overexploitation is the rule under such circumstances. Other anthropogenic

activities associated with changes in various marine pelagic ecosystems, such as increased

diseases, mortalities, extinctions, habitat invasions, and species replacements, function as

sentinels and indicate that portions of the pelagic ecosystem are under considerable stress. It is

argued that, without attention, these problems can be expected to worsen up to the year 2025 and

beyond. In addition to a comprehensive evaluation of status and trends relating to conservation of

the marine pelagic ecosystem, a second major objective is to evaluate whether current paradigms

of ecosystem function are sufficient to improve the ability of the scientific community to predict

future changes and to recommend relevant management strategies. This review differs from

previous ones by proposing that current conceptual models have failed to provide the basis for

accurately predicting patterns and features of pelagic communities, notably why specific organisms

occur where and when they do. It is argued that predation pressure is shaped by natural selection

in the sea as on land, and that it influences organism behaviour, life history strategy and

morphology, all of which determine marine pelagic ecosystem structure, and therefore should be

used to interpret function. From this perspective, attempting to understand present patterns and

predict the future of marine pelagic ecosystems, without understanding the intertwined roles of

evolution and predation in forging contemporary pelagic communities, is a hopeless endeavour. It is

proposed that both perspectives, resource availability and predation pressure, be incorporated into

a revised paradigm of pelagic ecosystem structure and function, a necessity if policies are to

predict anthropogenic impacts and environmental conservation is to be effective.

Keywords: marine, pelagic, ecosystem, pollution, extinction, invasions