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Natural dietary markers (stable isotopes and fatty acids) were used to determine the trophic structure and characterize carbon source(s) of juvenile and adult fishes associated with floating Sargassum in mid-shelf waters of the Gulf of Mexico. Stable carbon isotope ratios (d13C) of four autotrophs (Cladophora sp., phytoplankton [based on POM], Sargassum fluitans, Sargassum natans) were distinct (range:-16.3 to -21.0 ‰), with S. fluitans and S. natans enriched by 2-5 ‰ relative to Cladophora and POM. Stable nitrogen isotope ratios (d15N) of both S. fluitans and S. natans were depleted by 5 –7 ‰ compared to Cladophora and POM. The majority of d13C values of consumers were between -16 and -18 ‰, and d13C values were most depleted for juvenile shrimps, juvenile crabs, and certain juvenile fishes. Stable carbon isotope ratios of adult fishes varied from -16.1 to -17.5 ‰. Enrichment of δ15N occurred with increasing trophic position and the lowest values were observed for juvenile crustaceans, which ranged from 6.0 to 8.7 ‰. The majority of juvenile fishes were secondary heterotrophs (δ15N values ca. 8.0 to 11.0 ‰), while most adult fishes were tertiary consumers with δ15N values ranging from 11.9 to 14.3 ‰. Carbon source estimates from the two-source mixing model indicated that ~ 80 % of organic matter supplied to consumers (pooled across taxa) in the Sargassum complex was derived from POM. Fatty acid signatures of the primary producers were significantly different and used to further evaluate organic matter contribution to Sargassum-associated consumers. C22 polyunsaturated fatty acids (PUFAs) (22:6n-3, 22:5n-3) were most abundant in POM, while high levels of C18 and C20 PUFAs were observed for Cladophora and Sargassum (18:2n-6 and 20:4n-6, respectively). Consumer signatures were dominated by 22:6n-3. Principal component analysis indicated that fatty acid signatures of each of the six juvenile and six adult fish species were highly similar to POM and distinct from the other producers within the Sargassum complex. |
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fore more information: Rooker JR, Turner JP, Holt SA (2006) Trophic ecology of Sargassum-associated fishes in the Gulf of Mexico determined from stable isotopes and fatty acids. Mar Ecol Prog Ser 313:249-259. PDF Turner JP, Rooker JR (2006) Fatty acid composition of flora and fauna associated with Sargassum mats in the Gulf of Mexico. Journal of Marine Biology. PDF |
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Copyright 2006, Pelagic
Fisheries Conservation Program |
