Benthic food-web succession in a developing salt marsh

Abstract

Ecological succession has long been a focal point for research, and knowledge of underlying mechanisms is required if scientists and managers are to successfully promote recov- ery of ecosystem function following disturbance. We addressed the influence of bottom-up pro- cesses on successional assemblage shifts in salt marshes, ecosystems with strong physical gradi- ents, and how these shifts were reflected in the trophic characteristics of benthic fauna. We tracked the temporal development of infaunal community structure and food-web interactions in a young, created salt marsh and an adjacent natural marsh in Mission Bay, California, USA (1996−2003). Macro faunal community succession in created Spartina foliosa habitats occurred rapidly, with infaunal densities reaching 70% of those in the natural marsh after 1 yr. Community composition shifted from initial dominance of insect larvae (surface-feeding microalgivores) to increased dominance of oligo chaetes (subsurface-feeding detritivores) within the first 7 yr. Iso- topic labeling of microalgae, N2-fixing cyanobacteria, S. foliosa and bacteria revealed direct links (or absence thereof) between these basal food sources and specific consumer groups. In combina- tion with the compositional changes in the macroinvertebrate fauna, the trophic patterns indi- cated an increase in food-web complexity over time, reflecting resource-driven marsh succession. Natural abundance stable isotope ratios of salt marsh consumers (infaunal and epifaunal macroin- vertebrates, and fish) initially reflected distinctions in trophic structure between the created and natural marsh, but these diminished during successional development. Our findings suggest that changing resource availability is one of the important drivers of succession in benthic communi- ties of restored wetlands in Southern California.