Adding Texture and Relief to Seattle’s New Seawall, an Application of Ecological Engineering

The aftermath of the 2001 Nisqually earthquake revealed that Seattle’s seawall was decaying and in need of replacement. The resulting seawall replacement project presented an opportunity to replace vertical featureless walls with more complex and productive habitat. Several years before the new seawall was designed, the City of Seattle invited University of Washington biologists to participate in developing concepts for improved seawall habitat. This resulted in collaborations with several City of Seattle departments, during which we designed, deployed, and evaluated large habitat panels that tested several types of slopes and textures. Four years of monitoring algae, sessile invertebrates, and epibenthic organisms demonstrated that important biological “ecosystem engineers” benefited from adding texture and relief to seawalls. For example, compared to simple flat treatments and the existing seawall, recruitment of mussels was increased on panels with cobble texture, and rockweed was more abundant on high relief “finned” and “stepped” panels. Species richness of biota was also higher on surfaces with higher habitat complexity. This project represents a successful test of ecological engineering concepts, and the findings are being incorporated into the seawall that is currently being built. The City’s 10-year monitoring and adaptive management plan will allow for continued evaluation of these types of habitat enhancements on a larger scale. Invited comment: Mark Mazzola, Environmental Manager for the Seattle Department of Transportatio