, Volume 138, Issue 3, pp 325-332
Date: 19 Dec 2003

Trophodynamic linkage between river runoff and coastal fishery yield elucidated by stable isotope data in the Gulf of Lions (NW Mediterranean)

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Abstract

The link between climate-driven river runoff and sole fishery yields observed in the Gulf of Lions (NW Mediterranean) was analysed using carbon- and nitrogen stable isotopes along the flatfish food webs. Off the Rhone River, the main terrestrial (river POM) and marine (seawater POM) sources of carbon differed in δ13C (–26.11‰ and −22.36‰, respectively). Surface sediment and suspended POM in plume water exhibited low δ13C (–24.38‰ and −24.70‰, respectively) that differed more from the seawater POM than from river POM, demonstrating the dominance of terrestrial material in those carbon pools. Benthic invertebrates showed a wide range in δ15N (mean 4.30‰ to 9.77‰) and δ13C (mean −23.81‰ to −18.47‰), suggesting different trophic levels, diets and organic sources. Among the macroinvertebrates, the surface (mean δ13C −23.71‰) and subsurface (mean δ13C −23.81‰) deposit-feeding polychaetes were particularly 13C depleted, indicating that their carbon was mainly derived from terrestrial material. In flatfish, δ15N (mean 9.42 to 10.93‰) and δ13C (mean −19.95‰ to −17.69‰) varied among species, indicating differences in food source and terrestrial POM use. A significant negative correlation was observed between the percentage by weight of polychaetes in the diet and the δ13C of flatfish white muscle. Solea solea (the main polychaete feeder) had the lowest mean δ13C, Arnoglossus laterna and Buglossidium luteum (crustacean, mollusc and polychaete feeders) had intermediate values, and Solea impar (mollusc feeder) and Citharus linguatula (crustacean and fish feeder) exhibited the highest δ13C. Two different benthic food webs were thus identified off the Rhone River, one based on marine planktonic carbon and the other on the terrestrial POM carried by the river. Deposit-feeding polychaetes were responsible for the main transfer of terrestrial POM to upper trophic levels, linking sole population dynamics to river runoff fluctuations.