Habitat restoration as mitigation for lost production at multiple trophic levels

Abstract

Seagrass beds and salt marshes are important in the life histories of many fish, invertebrates, and aquatic birds, such that population size and production of these organisms can be limited by the loss of these habitats. Therefore, restoring seagrass or salt marsh would be expected to benefit species dependent on these resources. Following the 'North Cape' oil spill of January 1996 in Rhode Island (northeastern USA), habitat restoration was used to compensate for losses of fish, invertebrates, and aquatic birds. A habitat restoration model based on food-chain transfers was used to estimate equivalent production at the same trophic level as the losses, a novel approach that uses energetic efficiencies to scale across trophic levels. Benefits of habitat to each trophic level were estimated by assuming that the production of consumers is proportional to prey production gained by the restoration of habitat. The habitat restoration model balanced the losses with trophically equivalent production, discounting future gains in compensatory production relative to present losses such that interest is paid, analogous to economic discounting. Results showed that restoration of seagrass beds would be more productive than salt marsh restoration in southern New England and, likely, other temperate zone locations. Moreover, benthic faunal production in salt marshes could be accounted for by in situ primary production of angiosperms and benthic microalgae, whereas in seagrass beds, benthic faunal production exceeded that expected from in-bed primary production. The trophic model provides a methodology to estimate the scale of a restoration project that will provide production (ecological services) equivalent to losses of organisms at multiple trophic levels, applicable to natural resource damage assessments and other environmental assessments.