The primacy of top-down effects in shallow benthic ecosystems |
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| Authors: | K L Heck J F Valentine |
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| Institution: | 1.Dauphin Island Sea Lab,University of South Alabama,Dauphin Island |
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| Abstract: | Individual scientists, scientific organizations, and government agencies have all concluded that eutrophication is among the
most detrimental of all human activities in coastal ecosystems; very large amounts of funding have been earmarked to study
the negative consequences of nutrient pollution. Most studies of eutrophication have been conducted long after the numbers
and diversity of larger marine consumers were dramatically reduced by centuries of intense harvesting. It is now understood
that these once abundant predators played pivotal roles in regulating ecosystem structure and function, and that the widespread
overharvesting of large consumers can trigger indirect effects that alter species compositions in ways that are very similar
to those reported to result from eutrophication. All of this suggests that we should reevaluate whether the many negative
effects attributed to eutrophication are actually a result of nutrient additions or whether they may be the result of the
indirect effects of dramatically altered coastal food webs. In this essay, we review experimental assessments of the degree
to which changes in consumer abundances have indirectly altered the structure of benthic ecosystems in coastal waters, and
on the relative importance of top-down and bottom-up effects on coral reefs, rocky shores, and seagrass meadows. We find that
the evidence clearly indicates that indirect consumer effects are the primary drivers of coastal benthic ecosystem structure
and function. |
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