MEPS 428:49-61 (2011)  -  DOI: https://doi.org/10.3354/meps09052

ABSTRACT: Mangroves provide important habitats for many species throughout the tropics and subtropics. But the direct contribution of mangrove productivity to associated food webs through trophic interactions varies depending on site-specific context. We used stable isotopes to examine trophic structure among major habitat types associated with 2 fringing mangrove areas in Shark Bay, Western Australia, a nearly pristine ecosystem. The only mangrove species, Avicennia marina, had a distinctive δ¹³C isotopic value, which allowed direct testing of the hypothesis that consumers relied on mangrove-derived production. We found little evidence to support this hypothesis in isotope values of invertebrates or fish from 4 different feeding guilds. Within the species of fish we were able to sample, variation in δ¹³C and δ¹⁵N stable isotope values occurred over spatial scales of hundreds of meters. Some of this variation is consistent with the spatial mosaics of seagrass, sand flat and mangrove habitats available to fish. In a nearly pristine system, fish captured in mangrove systems show fine scale variability in stable isotope values, but we found no indication that mangrove productivity directly supported local fish populations through the trophic web.

KEY WORDS: Energy flow · Fish · Food web · Seagrass · Stable isotope analysis · Australia