Epibenthic invertebrates of natural and constructed marshes of San Diego Bay

To aid in assessing the functioning of a constructed salt marsh and the adjacent natural marsh, we conducted a one-year study of epibenthic invertebrates using a new sampling method. Invertebrates were trapped in litter bags (5-mm mesh) filled with Spartina foliosa; these were compared with bags containing other substrates (plastic grass, Typha, and Scirpus, all of which trapped fewer individuals than Sparrina-filled bags. A total of 168 Spartina-filled bags trapped 43,531 individuals over 8 sampling dates. Invertebrate abundances differed by season, elevation, cover of Spartina, and marsh type. There were more invertebrates trapped in fall than in winter; there were more in the lower than higher elevation, and in the natural marsh, there were twice as many invertebrates in areas with greater than or equal to 80% cover of Spartina than with less than or equal to 20% cover. The strongest pattern was with marsh type. Natural, fully vegetated marsh had 2-3 times as many individuals as the sparsely-vegetated, 4-year-old constructed marsh. Overall, the most abundant species was a larval dipteran, Pericoma sp., which was up to 9 times more abundant in the natural marsh. An anemone, Diadumene franciscana, was virtually restricted to the natural marsh. However, the more open constructed marsh had significantly more Hemigrapsus oregonensis crabs and more exotic mussels (Musculista senhousia). The invertebrate assemblage in the 4-year-old marsh was not equivalent to that of the natural marsh. Both marshes had 37 species, but species lists were 46% similar for all sites and dates combined, and relative abundances were 67% similar. Coarser sediment, lower organic matter, and sparse vegetative cover were potential causes of significantly lower abundances in the constructed marsh.