Beyond acres and turions: Improving metrics for eelgrass mitigation

Native eelgrass (Zostera marina) provides a wide variety of ecological functions that support nearshore ecosystems, and is one of the only rooted vascular marine plants on the West Coast. Recognition of the functions provided by eelgrass has led to increasing regulatory attention and scrutiny of projects with the potential to affect eelgrass systems. In 2014, the National Oceanic and Atmospheric Administration published guidance for projects that impact eelgrass habitat: the California Eelgrass Mitigation Policy (CEMP). This guidance provides a framework for mitigation associated with projects that impact eelgrass habitat. However, it fails to account for projects that may co-exist with eelgrass habitat, or where effects to eelgrass beds are limited or transitory. While the CEMP recognizes that there are ecological functions provided by shellfish aquaculture, there is no guidance on how to calculate changes to functions by adding shellfish to eelgrass habitat.

A framework for a credit-debit accounting system for marine habitats was developed using an accounting tool from wetland ecology. The credit-debit framework is designed to provide guidance on how to value three ecological functions: (1) water quality, (2) habitat structure, and (3) prey resources. These functions support over 90% of the importance for which eelgrass is recognized. A set of questions was established for each function that values a habitat based on site potential, landscape context, and watershed or regional priorities. This framework is intended to initiate a detailed conversation about how to value ecological functions associated with a variety of marine habitats, including eelgrass, shellfish aquaculture, mudflat, and salt marsh.