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    2. closing an area may lead to increased human impacts on open areas;

    3. to protect some species effectively, a reserve would have to be so large that it would be infeasible to implement and enforce; and

    4. reserves, in general, will not be effective without continued conventional management of the area outside the reserves.

The primary advantages of using a spatial approach are

    1. reserves should be relatively simple and inexpensive to enforce once the boundaries are established and recognized;

    2. regulations may be tailored to specific habitats within the jurisdiction of regional management authorities (e.g., zoning seagrass beds as off-limits to destructive fishing gears);

    3. reserves support conservation of the full range of marine resources, including habitat, biological diversity, and exploited species such as commercial fish stocks;

    4. reserves provide unique sites for education and research on marine ecosystems, especially for comparison to areas altered by human activities; and

    5. reserves provide “control” areas for determining natural mortality rates for different life-history stages, rates that are critical variables in stock assessment models (Box 5-1).

However, a marine reserve is envisioned to play a role in the ecosystem on a scale larger than its boundaries (Agardy, 1994). Reserves that are intended to fill heritage needs—for instance, to protect endangered species, collapsed habitat, or special features—could also provide protection for other vulnerable species that may support the recovery of areas disturbed by human activities. Examples include reserves for a habitat such as the Oculina Banks coral beds of eastern Florida (Koenig et al., 2000) or reserves intended to protect a specific geological feature such as the Texas Flower Gardens coral reefs (Gittings and Hickerson, 1998).

Preserve and Restore Habitat

Both biological diversity and productivity are fundamentally dependent on habitat, and loss of habitat is the leading cause of declining biodiversity (Wilcove et al., 1998; Wilcove and Wilson, 2000). In concept, reserves can protect and restore habitats that are critical for living marine resources. Structurally complex biological habitats often shelter breeding aggregations, provide nursery habitat, and supply food for adults (Ebeling and Hixon, 1991; Lindholm et al., 1999). Studies of areas in which the structural integrity of the habitat has been lost typically show a clear reduction in biomass and biodiversity (Dayton et al., 1995; Morton, 1996; Watling and Norse, 1998; Lindeman and Snyder, 1999; Koenig et al., 2000).

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