Effects of spatial and temporal heterogeneity on fish use and trophic structure in a restored tidal marsh

Ecological theory predicts that greater incorporation of habitat heterogeneity in restoration should enhance diversity and key functions. Topographic heterogeneity mediates hydrology and broadly impacts structure and function, from genetic to ecosystem scales. In arid-lands restoration, 10-20 cm deep pits collect water and function as nodes of biotic recovery. In intertidal wetlands, subtler variations (1-3 cm) are important due to frequent water level oscillations.; In a large-scale (8-ha) southern California experimental restoration site, we tested the role of topographic heterogeneity on trophic structure and fish use of salt marsh habitat. Shallow pools were important for fishes because they provided unique habitats and invertebrate prey. Pools were a preferred microhabitat for Fundulus parvipinnis (California killifish) even when the entire marsh was inundated. At a larger scale, areas with topographic heterogeneity in the form of replicate tidal creek networks supported more frequent occurrence of Gillichthys mirabilis (longjaw mudsucker) than areas without creeks. We propose a conceptual model for tidal wetlands wherein creeks function as "conduits" that enhance connectivity between subtidal and intertidal habitat and pools serve as "oases" of elevated prey resources.; We created shallow pools to mimic geomorphological processes and subjected them to experimental bottom-up (nitrogen fertilization) and top-down (fish exclusion) treatments. Pools quickly developed abundant invertebrate prey (within 4-weeks), with densities exceeding those found in older, "natural" pools. Some measures of algal biomass were increased by nitrogen addition but there were no upward-cascading effects on invertebrate composition or abundance. Fish abundance in the site varied seasonally but there were no compelling effects of fish exclusion treatments on algal or invertebrate abundance.; In a young restored marsh, with limited plant cover and subject to disturbances, multiple forms of heterogeneity helped to restore trophic function by enhancing feeding opportunities for consumers. Natural systems are heterogeneous, not simple, and we should mimic this complexity in our restoration efforts.