Benthic macrofauna–habitat associations in Willapa Bay, Washington, USA

Estuary-wide benthic macrofaunaehabitat associations in Willapa Bay, Washington, United States, were determined for 4 habitats (eelgrass [Zostera marina], Atlantic cordgrass [Spartina alterniflora], mud shrimp [Upogebia pugettensis], ghost shrimp [Neotrypaea californiensis]) in 1996 and 7 habitats (eelgrass, Atlantic cordgrass, mud shrimp, ghost shrimp, oyster [Crassostrea gigas], bare mud/sand, subtidal) in 1998. Most benthic macrofaunal species inhabited multiple habitats; however, 2 dominants, a fanworm, Manayunkia aestuarina, in Spartina, and a sand dollar, Dendraster excentricus, in subtidal, were rare or absent in all other habitats. Benthic macrofaunal BrayeCurtis similarity varied among all habitats except eelgrass and oyster. There were significant differences among habitats within- and between-years on several of the following ecological indicators: mean number of species (S ), abundance (A), biomass (B), abundance of deposit (AD), suspension (AS), and facultative (AF) feeders, Swartz’s index (SI), Brillouin’s index (H), and jackknife estimates of habitat species richness (HSR). In the 4 habitats sampled in both years, A was about 2.5 greater in 1996 (a La Nin˜a year) than 1998 (a strong El Nin˜o year) yet relative values of S, A, B, AD, AS, SI, and H among the habitats were not significantly different, indicating strong benthic macrofaunaehabitat associations despite considerable climatic and environmental variability. In general, the rank order of habitats on indicators associated with high diversity and productivity (high S, A, B, SI, H, HSR) was eelgrass ¼ oyster Atlantic cordgrass mud shrimp bare mud/sand ghost shrimp ¼ subtidal. Vegetation, burrowing shrimp, and oyster density and sediment %silt þ clay and %total organic carbon were generally poor, temporally inconsistent predictors of ecological indicator variability within habitats. The benthic macrofaunaehabitat associations in this study can be used to help identify critical habitats, prioritize habitats for environmental protection, index habitat suitability, assess habitat equivalency, and as habitat value criteria in ecological risk assessments in Willapa Bay.