Abstract
Mangrove and seagrass habitats are important components of tropical coastal zones worldwide, and are conspicuous habitats of Centla Wetland Biosphere Reserve (CWBR) in Tabasco, Mexico. In this study, we examine food webs in mangrove- and seagrass-dominated habitats of CWBR using stable isotope ratios of carbon and nitrogen. Our objective was to identify the importance of carbon derived from mangroves and seagrasses to secondary production of aquatic consumers in this poorly studied conservation area. Carbon and nitrogen isotope ratios of basal sources and aquatic consumers indicated that the species-rich food webs of both habitats are dependent on riparian production sources. The abundant Red mangrove Rhizophora mangle appears to be a primary source of carbon for the mangrove creek food web. Even though dense seagrass beds were ubiquitous, most consumers in the lagoon food web appeared to rely on carbon derived from riparian vegetation (e.g. Phragmites australis). The introduced Amazon sailfin catfish Pterygoplichthys pardalis had isotope signatures overlapping with native species (including high-value fisheries species), suggesting potential competition for resources. Future research should examine the role played by terrestrial insects in linking riparian and aquatic food webs, and impacts of the expanding P. pardalis population on ecosystem function and fisheries in CWBR. Our findings can be used as a baseline to reinforce the conservation and management of this important reserve in the face of diverse external and internal human impacts.
Highlights
Mangroves are an important vegetation type fringing tropical continental margins (Hogarth, 2007)
These mangrove species had δ13C values between 29.91 and -26.29‰, similar to carbon isotope signatures observed for the riparian vegetation at San Pedrito Lagoon (e.g. Phragmites australis, Thalia geniculata and Typha latifolia; Table 1, Fig. 2)
Carbon isotope signatures were similar across the tree species found at the mangrove creek, values of δ15N were highly variable among species, ranging from 3.07‰ for the Black mangrove Avicennia germinalis to 8.10‰ for the White mangrove Laguncularia racemosa (Table 1, Fig. 2)
Summary
Mangroves are an important vegetation type fringing tropical continental margins (Hogarth, 2007). They are highly productive, varying according to species composition, soil salinity, degree of tidal inundation, nutrient availability and photosynthetic capacity (Nichols et al, 1985; Sobrado, 1999; Sobrado & Ball, 1999). Previous research indicates that carbon derived from mangroves is often less important as an energy source for aquatic consumers, primarily fishes, than that derived from nearby marine seagrass ecosystems (Rodelli et al, 1984; Bouillon et al, 2002; Sheridan & Hays, 2003; Nagelkerken & Velde, 2004a, 2004b). Aquatic consumers in isolated mangrove creeks may be expected to rely more heavily on mangrove-derived carbon than aquatic consumers in mangrove habitats with high connectivity to seagrass beds
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