Stage structure, density dependence and the efficacy of marine reserves
Authors: St. Mary, Colette M.; Osenberg, Craig W.; Frazer, Thomas K.; Lindberg, William J.
Source: Bulletin of Marine Science, Volume 66, Number 3, May 2000 , pp. 675-690(16)
Abstract:The habitat requirements of fishes and other marine organisms often change with ontogeny, so many harvested species exhibit such extreme large-scale spatial segregation between life stages that all life stages cannot be protected within a single marine reserve. Nevertheless, most discussions of marine reserves have focused narrowly on single life-history events (e.g., reproduction or settlement) or a single life stage (e.g., adult or recruit). Instead, we hypothesize that an effective marine reserve system should often include a diversity of protected habitats, each appropriate to a different life stage. In such a case, the spatial configuration of habitats within reserves, and of separate reserves across larger spatial scales, may affect how marine resources respond to reserve design. We explored these issues by developing a mathematical model of a fish population consisting of two benthic life stages (juvenile and adult) that use spatially distinct habitats and examined the population's response to various management scenarios. Specifically, we varied the sizes of reserves protecting the two life stages and the degree of coupling between juvenile and adult reserves (i.e., the fraction of the protected juvenile stock that migrates into the adult reserve upon maturation). We examined the effects when density dependence operated in only the juvenile stage, only the adult stage, or both. The results demonstrated that population stage structure and the nature of density dependence should be incorporated into the design of marine reserves but did not provide robust support for the general tenet that all life stages must be protected for an effective reserve system. The results indicated that biological considerations, alone, were insufficient for design of the optimal marine reserve. Instead, it was necessary to consider the value (e.g., socioeconomic or ecological) of each biological outcome; under some value functions, a mixed strategy (i.e., protecting both life stages) was best, whereas for others, the best solution focused on a single life stage. Resolving issues of marine reserve design, especially for stage-structured populations, will require more detailed study of stage-structured populations and a more explicit integration of biological and socioeconomic models.
Document Type: Research Article
Publication date: May 1, 2000
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