Macrobenthos of Spartina foliosa (Pacific Cordgrass) Salt Marshes in Southern California: Community Structure and Comparison to a Pacific Mudflat and a Spartina alterniflora (Atlantic Smooth Cordgrass) Marsh

Abstract

Environmental attributes (vegetation and sediment properties) of and macrofaunal community structure in sediments of five southern California Spartina foliosa marshes (San Diego Bay, Mission Bay, Upper Newport Bay, Bolsa Chica Lagoon, and Anaheim Bay) were examined during October 1994. Macrofaunal densities in Pacific S. foliosa marshes (avg. 122,268 indiv. m2>300 μm) were 3 to 10 times higher than observed in Atlantic S. alterniflora and S. anglica marshes. The macrofauna of S. foliosa marshes was composed mainly of enchytraeid, naidid, and tubificid oligochaetes (66%), with the enchytraeids dominant at all sites except Bolsa Chica Lagoon. Polychaetes, insects, and peracarid crustaceans accounted for most of the remaining fauna. Multivariate analyses indicated greatest faunal similarity between the two southernmost marshes (Mission Bay and San Diego Bay), and between Anaheim and Newport Bay marshes, with Bolsa Chica Lagoon exhibiting a distinct assemblage. There were strong positive associations of faunal abundance and composition with percent organic matter and percent open area, and negative associations with percent sand and dry weight of algae. For the vegetated marsh in Mission Bay, faunal comparisons were made with an adjacent mudflat and with a S. alterniflora marsh in North Carolina, USA. The unvegetated mudflat exhibited similar macrofaunal densities but higher species richness than the adjacent Spartina marsh. The macrofaunal assemblage of the Mission Bay S. foliosa marsh differed from that of the Atlantic S. alterniflora marsh and the Pacific mudflat in having a greater proportion of oligochaetes, especially Enchytraeidae, and fewer polychaetes. This study represents the first published description that we are aware of for macrofauna in S. foliosa vegetated marsh sediments. The findings document faunal variation among southern California embayments and suggest that differences in macrobenthic community structure occur between marsh and mudflat habitat as well as between east and west coast Spartina marshes. Observed differences may have significant implications for wetland conservation and restoration efforts.