Food web analysis of southern California coastal wetlands using multiple stable isotopes

Abstract

Carbon, nitrogen, and sulfur stable isotopes were used to characterize the food webs (i.e., sources of carbon and trophic status of consumers) in Tijuana Estuary and San Dieguito Lagoon. Producer groups were most clearly differentiated by carbon, then by sulfur, and least clearly by nitrogen isotope measurements. Consumer N isotopic enrichment suggested that there are four trophic levels in the Tijuana Estuary food web and three in San Dieguito Lagoon. A significant difference in multiple isotope ratio distributions of fishes between wetlands suggested that the food web of San Dieguito Lagoon is less complex than that of Tijuana Estuary. Associations among sources and consumers indicated that inputs from intertidal macroalgae, marsh microalgae, and Spartina foliosa provide the organic matter that supports invertebrates, fishes, and the light-footed clapper rail (Rallus longirostris levipes). These three producers occupy tidal channels, low salt marsh, and mid salt marsh habitats. The only consumer sampled that appears dependent upon primary productivity from high salt marsh habitat is the sora (Porzana carolina). Two- and three-source mixing models identified Spartina as the major organic matter source for fishes, and macroalgae for invertebrates and the light-footed clapper rail in Tijuana Estuary. In San Dieguito Lagoon, a system lacking Spartina, inputs of macroalgae and microalgae support fishes. Salicornia virginica, S. subterminalis, Monanthochloe littoralis, sewage- derived organic matter, and suspended particulate organic matter were deductively excluded as dominant, direct influences on the food web. The demonstration of a salt marsh-channel linkage in these systems affirms that these habitats should be managed as a single ecosystem and that the restoration of intertidal marshes for endangered birds and other biota is compatible with enhancement of coastal fish populations; heretofore, these have been considered to be competing objectives.

Temporal and spatial variability in stable isotope compositions of a freshwater mussel: implications for biomonitoring and ecological studies

“…The survey of E. complanata from 22 streams in North Carolina corroborates other studies demonstrating spatial stratiWcation of bivalve stable nitrogen and carbon isotope signatures by site (McKinney et al 1999; Post et al 2000) or land-use (Fry 1999;McKinney et al 2002) characteristics. We found a positive association between dissolved 15 N-NO 3 and corresponding mussel tissue signatures across sites, consistent with the speculated relationship between bivalve 15 N composition and nutrient loading in ambient waters (Cabana and Rasmussen 1996;Hansson et al 1997;Kwak and Zedler 1997;McClelland and Valiela 1998). Although the association between resident mussel signatures and a site's water signature was statistically signiWcant, the two compartments were not tightly correlated.…”

Dietary Segregation of Pelagic and Littoral Fish Assemblages in a Highly Modified Tidal Freshwater Estuary

“…Food resources from SAV could also be inferred for omnivorous species, such as the golden shiner and hitch, which had mean d 13 C signatures less than À21%. Based on the enriched d 13 C signatures of most consumers in open-water shoals, a terrestrial-or marsh-derived food web pathway is not substantiated (Kwak and Zedler 1997;Howe and Simenstad 2007). Rather, our findings highlight the importance of energy imports from adjacent SAV as the primary subsidy to consumers in open-water shoals (Hyndes and Lavery 2005;Melville and Connolly 2005;Cardona et al 2007).…”

“…In other estuaries, intertidal shoals are key habitats where fishes reside to gain access to marsh plains during flood tides (Weisberg et al 1981;Kneib 1984;Madon et al 2001) or to escape predators from deep subtidal waters (Kneib 1987) or adjacent SAV habitats (Rozas and Odum 1988). We believe that creation of open-water shoals would promote native fish use in littoral areas; however, companion research on the functions of this habitat are needed to address uncertainty associated with long-term sustainability of this habitat and native fish populations in the estuary (Kwak and Zedler 1997;Madon 2008). …”

“…A variety of organic carbon sources may support coastal and estuarine consumers, including phytoplankton (Canuel et al 1995;Deegan and Garritt 1997;Sobczak et al 2002;Howe and Simenstad 2007), submerged aquatic vegetation (SAV;Fry 1981;Kitting et al 1984), benthic algae (Hecky and Hesslein 1995;Deegan and Garritt 1997;Kwak and Zedler 1997;Page 1997), epiphytic macroalgae (Kitting et al 1984;Moncrieff and Sullivan 2001;Vizzini et al 2002), and terrestrial vegetation (Chanton and Lewis 2002).…”

Food web analysis in two permanently open temperate estuaries: Consequences of saltmarsh loss?

“…Where estuarine foodwebs are reliant on significant inputs from fringing saltmarsh and macrophytes, there is the potential for flow-on effects to higher trophic levels, such as large invertebrates and fish (e.g. Loneragan and Bunn 1997;Kwak & Zedler 1997). However, the literature suggests a varied role for this material in the diet of estuarine organisms.…”