A method for estimating marine habitat values based on fish guilds, with comparisons between sites in the Southern California Bight

Habitat valuation is an essential tool for tracking changes in habitat qual ity and in adjudicating environmental mitigation. All current methods for e stimating habitat values of coastal marine sites rely heavily on the opinio n of experts or on data variables that can readily be manipulated to influe nce the outcome. As a result, unbiased, quantitative comparisons between th e values of different marine habitats are generally unavailable. We report here on a robust, objective technique for the valuation of marine habitats that makes use of data that are commonly gathered in surveys of marine fish populations: density, fidelity, and mean size. To insure comparability acr oss habitats, these variables are assessed for guilds of fishes, rather tha n for single species. The product of the three guild-based parameters is tr ansformed to its square root and then summed across all guilds in the habit at, yielding a single measure of habitat value for each site surveyed. To d emonstrate the usefulness of this approach, we have analyzed data from exis ting surveys of 13 marine sites in the Southern California Eight, encompass ing 98 fish species from 23 guilds. For seven of the sites, it was possible to develop estimates of the confidence interval of the habitat valuation, using a resampling technique. Variance estimates from resampling in one hab itat mirrored those derived from analysis of annual variation. The resultan t ranking of habitat types was: kelp beds > shallow artificial reefs > wetl ands > protected shallow waters (soft bottom) > shallow open coastal sand ( depth <30 m) > soft bottom habitat on the continental shelf (30 m < depth < 200 m) > soft bottom habitat on the continental slope (depth >200 m). Altho ugh our data sets were restricted to Southern California, similar data coul d be obtained from any reasonably well-studied marine environment. The guil d-based valuation technique may, therefore, be broadly applicable to the an alysis of other marine ecosystems.