Publisher :
Place of publication :
Publication year : 2004
Thematic : Marine Resources
Language : English
Note
The rigorous demonstration of truly stable alternate community states is elusive in marine
ecosystems and might remain so for some time. Examples of marine community states that have shifted
are nevertheless increasingly conspicuous. The growing concern over these altered community states is
often related to questions of persistence and reversibility, especially when these shifted states are
considered to be degraded. I used empirically-based trophic models and direct empirical field studies to
explore the potential of particular hypothesized mechanisms to generate and maintain alternate
community states in four marine ecosystems: a Galápagos rocky reef, Prince William Sound, Alaska, the
West Florida Continental Shelf, and coral reefs of the Spermonde Archipelago or Southwest Sulawesi,
Indonesia.
Construction and analysis of an Ecopath with Ecosim (EwE) model of a Galápagos rocky reef
indicated that the unsustainable fishery targeting the holothurian Stichopus fuscus can, by itself, trigger
the replacement of previously diverse reef platform communities with Aiptasia sp. anemone barrens.
Construction and analysis of a Prince William Sound, Alaska EwE model indicated that severe
disturbances such as the Exxon Valdez oil spill can shift a marine biotic community to an alternate state
that persists in a stable manner for decades, and that the character of such disturbances, in terms of their
breadth and community-level life-history signatures, might strongly influence whether a community shifts
to an alternate state. In addition, a search for keystone species provided a whole-system approach to
identifying species or functional groups whose depletion or removal might have the most severe
consequences for community structure, and the most potential for mediating shifts.
Construction and analysis of a West Florida Shelf EwE model indicated that increased sea floor
shading by coastal phytoplankton (i.e., resulting from nutrient runoff pollution) can cause broad shifts in
this continental shelf community by shading benthic primary producers, which support much of the
overall shelf community.
An empirical field study of monsoons and runoff in Southwest Sulawesi, Indonesia indicates
some of the mechanisms involved in shifting tropical reefs from coral-dominated to algae-dominated
systems.
These contributions feature some newly emerging approaches for gaining insights into marine
communities and for developing hypotheses that can be more rigorously evaluated in the future. None of
these examples, however, are comprehensive or strictly falsificationist by themselves. The continued
integration of these emerging community/ecosystem modeling approaches with direct empirical studies
should vastly increase the potential for distinguishing the relative roles of natural and anthropogenic
forces in shaping marine communities. The goal of the first steps described here was to identify particular
mechanisms in each example that have the potential to generate or maintain community shifts.
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Keywords : Lepus sinensis
Encoded by : Pauline Carmel Joy Eje
