Are deep-water corals important habitats for fishes?

Abstract

High densities of fishes in aggregations of deep-water corals (e.g., of the genera Primnoa, Paragorgia, Paramuricea) do not necessarily indicate that corals are important habitats in terms of population processes. Frequency dependent distribution models provide a basis for assessing the role of deep-water corals. It is necessary to understand the overall habitat-related distributions of fish species, at particular life history stages, in order to assess the particular role of corals. Examining the landscape for ecologically equivalent habitats is one approach for assessing the importance of coral habitats. Measures of the functional equivalence of habitats are demonstrated, as an example, for sites from the Gulf of Maine on the northeast United States continental shelf. Fish census data based on surveys with a remotely operated vehicle in 2003 showed that communities in habitats dominated by dense corals and dense epifauna were functionally equivalent when compared with five other less complex habitats (e.g., boulder with sparse coral cover). Comparison of species-individual curves showed that sites with dense coral and dense epifauna habitats supported only moderate levels of fish diversity when compared with other sites. Further, density of Acadian redfish (Sebastes fasciatus) in dense coral and dense epifauna habitats, where this species was dominant, was not statistically different but was higher than an outcrop-boulder habitat with sparse epifauna (the only other site where this species was abundant). Such data suggest that coral habitats are not necessarily unique but have attributes similar to other important habitats. However, the level of their importance in the demography of fish populations and communities remains to be demonstrated. Focusing conservation efforts for deep-water corals on their perceived value to exploited species, without good demographic information on fish populations, may ultimately leave corals open to destructive fishing practices if new and contrary information emerges. Conservation efforts for corals, in the absence of explicit ties to managed fish species, might do better emphasizing the intrinsic value of corals, their slow growth, high sensitivity to disturbance, and the questionable potential for recovery.