Tidal flat macrofaunal communities and their associated environments in estuaries of southern California and northern Baja California, Mexico

Several tidal flats in both Estero de Punta Banda and Bahia de San Quintin, Baja California, and one in Mission Bay, southern California, were sampled for macrofaunal properties (taxonomic composition, density, species richne ss, and functional groups for animals greater than or equal to 0.3 mm) and associated environmental variables (sediment properties, salinity, plant be lowground biomass, and cover of Zostera marina) in order to establish a ben chmark data set for these areas. The grouping of macrofauna into higher tax onomic or functional groups for these comparisons reduced variability and r evealed stronger relationships. Each estuary had a fairly distinct macrofau nal assemblage, with that of Estero de Punta Banda being different from Bah ia de San Quintin and Mission Bay primarily due to dominance by a capitelli d polychaete, lower proportions of surface deposit feeders, and higher prop ortions of fauna with a planktonic stage. The flats in Mission Bq and Bahia de San Quintin were dominated by peracarid crustaceans, oligochaetes and p olychaetes and had higher proportions of direct developers and macrofauna w ith mobile adult stages than did Estero de Punta Bands. There was an overla p of the environmental characteristics among estuaries, with more variabili ty of sediment and vegetation properties within than among estuaries. Withi n Bahia. de San Quintin, there was an oceanic to back-bay distribution grad ient of macrofauna that was similar to that found in estuaries in wetter cl imates, despite the lack of a salinity gradient in San Quintin. A decouplin g of the benthos and the assumed anthropogenic stresses was observed with t he degraded site, Mission Bay, being most similar to the relatively pristin e Bahia de San Quintin. Selection of reference sites and sampling variables should be made cautiously because effects of disturbance factors on the be nthos may be site-dependent, scale-dependent, or negligible.