Nurseries

In aquatic and especially marine environments, certain estuarine habitat types are commonly thought to serve as nurseries for particular species. Although they are rarely defined explicitly, by labeling a habitat a nursery, one implies that this habitat may be disproportionately important (relative to other habitats) in supporting juveniles that eventually enhance the adult population of a given species. The nursery concept also implies that organisms move among different habitats during the course of their life cycles, starting in nurseries and perhaps other suboptimal habi tats before differentially moving on to subadult and adult habitats. In other words, only species with developmental (or ontogenetic) shifts in their habitat usage have nursery habitats. Habitats that are traditionally considered to be nursery zones for many species, including sea-grass meadows, mangroves, algal beds, and marshes, typically provide important three-dimensional structure as well as good ecosystem productivity for juveniles to exploit. Mangroves and healthy seagrass meadows, for example, are frequently cited as providing nursery habitats for various coral reef fishes, while certain types of algal beds are important for other reef fishes and spiny lobsters (Panulirus spp.). Lemon sharks (Negaprion brevirostris) also use certain lagoons with seagrass beds as nurseries before dispersing as adults. Other species are thought to take advantage of the

Mangroves, such as this one on Lizard Island near Queensland, Australia, provide nursery habitats for various coral reef fishes. (Mark A. Johnson/CORBIS)

structure and productivity of oyster reefs as well as rocky reefs with algae.

For adult population enhancement to occur via nursery habitats, some combination of factors is necessary. These nursery habitats should, relative to the average for all habitats, (1) support higher juvenile population densities, (2) produce increased juvenile growth rates, (3) promote increased juvenile survivorship, and (4) facilitate greater movement from juvenile to adult habitats. Since gathering data across all these areas would be difficult, and management decisions regarding the fate of potentially important nursery habitat areas usually need to be made quickly, scientists must frequently use the best data available to make assessments about the importance of specific areas for fisheries populations. Since there is often general evidence supporting the importance of certain habitat types (for example, seagrass meadows) for a given species, but all expanses or patches of this habitat are probably not equally important, the next step involves estimating which specific habitat patches are likely to be of greatest value for conservation. Issues such as habitat patch quality or health, size, likelihood of disturbance, and proximity to subadult and adult habitats (to maximize movement between habitats) are critical for this determination.

—Daniel R. Brumbaugh

See also: Arthropods, Marine; Bony Fishes; Chon-drichthyes; Coastal Wetlands; Coral Reefs; Estuaries; Lagoons; Preservation of Habitats

Bibliography

Beck, Michael W., et al. 2001. "The Identification, Conservation, and Management of Estuarine and Marine Nurseries for Fish and Invertebrates." BioScience 51, no. 8:633-641.

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