Spatial and temporal forcing of macrobenthic succession in a restored coastal salt marsh
Lisa A. Levin and Theresa S. Talley
Studies of ecosystem recovery following wetland restoration offer scientists an exceptional opportunity to learn about structure, function and successional processes in salt marsh ecosystems, particularly when controlled experiments can be performed. This study employed mensurative and manipulative methods to examine the potential influence of vascular vegetation and soil organic matter on the rate and trajectory of macrofaunal recovery in a southern California created salt marsh, the Crown Point Mitigation Site (CPMS) during the first 3 years of establishment (1996-1999). Macrofaunal density and species richness recovered rapidly within the CPMS Spartina foliosa zone; densities in the created marsh were < 10% those in the natural marsh after 4 months, 50% after 16 months and 97% after 28 months. Early successional stages involve a significantly lower proportion of tubificid and enchytraeid oligochaetes, and a significantly higher proportion of chironomids and other insect larvae than the mature stages characterizing the natural marsh. The most common mode of macrofaunal entry into the created marsh was rafting on seagrass and algae by juveniles and adults via a tidal channel connected the adjacent natural marsh. Initial planting of S. foliosa had no influence on macrofaunal recovery, in part because of the variable survival of the cordgrass. However, both positive and negative correlations were noted between Spartina and Salicornia shoot density and densities of specific macrofaunal taxa. Soil organic matter (below-ground biomass, combustible organics, and chlorophyll a) was strongly correlated with macrofaunal densities, but not species richness. Soil amendment with kelp, alfalfa, and peat had little influence on faunal densities. Addition of Milorganite (a sewage product) promoted similarity to the natural system by enhancing development of enchytraeid and tubificid oligochaete assemblages. Overall, the most rapid faunal recovery was observed in highly localized, organic-rich marsh sediments remaining from the historical wetland. In addition, rising sea level associated with the 1998 El Nino appeared to promote similarity of macrofaunal communities between the created and adjacent natural marsh. We conclude that natural spatial and temporal heterogeneity in the system are likely to exert stronger influence on succession in southern California wetlands than manipulations of vegetation or soil properties.
September 7, 2006
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