Creation of Rocky Intertidal and Shallow Subtidal Habitats to Mitigate for the Construction of a Large Marina in Puget Sound, Washington

Development of a 1,200-slip marina in Puget Sound, Washington (USA), required the construction of mitigation to offset the loss of intertidal rearing habitat that is important to outmigrating juvenile salmon. Monitoring the mitigation areas to evaluate the production of important food organisms (epibenthic zooplankton) for juvenile salmon and resident marine fish was a critical element in the permitting of the marina. We discuss the mitigation approach and the preliminary results of the monitoring program. Mitigation to compensate for losses of fish rearing habitat included: (1) creation of 3.2 ha (8 ac) of rocky beach and kelp habitat in the 0 to −2.5 m (0 to −8 ft) bottom elevation range (located east and west of the marina); and (2) construction of 2.0 ha (5 ac) of new beach within the marina. Monitoring began in 1991 and will continue through 1996. The mitigation habitat provided interstitial refuge for epibenthic organisms and structure for the attachment of algae. Micro- and macro-algae growing on rocky subtidal and beach mitigation habitats were found to be an important habitat for the epibenthic animals. These results were consistent with other investigations showing that areas of increased algae and seagrass density, or biomass, contained more species and a greater abundance of epibenthic invertebrates than did areas of lower vegetative cover or structure. The original mitigation goal, to replace “in-kind” food resource production on intertidal and subtidal cobble and gravel habitats lost due to marina construction, appears to be feasible, at least in the short term.