Food web analysis of southern California coastal wetlands using multiple stable isotopes |
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Authors: | T J Kwak Joy B Zedler |
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Institution: | (1) Pacific Estuarine Research Laboratory, Department of Biology, San Diego State University, San Diego, CA 92182, USA, US |
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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 15N 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.
Received: 24 April 1996 / Accepted: 24 October 1996 |
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Keywords: | Food web Restoration Salt marsh Stable isotopes Wetland |
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