Links between introduced fish and zooplanktonic and zoobenthic food sources in the food webs of two reservoirs of a semi-arid zone in Algeria

Few studies have focused on the trophic functioning of the reservoirs in Algeria. The study of the gut contents of fish species, as well as the analysis of the stable isotopes of(13)C and(15)N in the environment, were carried out on samples collected during spring 2010 in two reservoirs: Ghrib and Harreza of the upper Cheliff plain (Algeria) within a semi-arid climate zone. In each of the reservoirs,C-13 and(15)N were measured in sediments, particulate organic matter (POM), macrophytes, zooplankton, zoobenthos and fish. The isotopic analysis shows that the carbon values that supply both reservoirs, Ghrib and Harreza, were -31.16 +/- 0.05 <C-13 < -18.01 +/- 0.21 parts per thousand and -30.82 +/- 0.07 <C-13 < -17.24 +/- 3.50 parts per thousand, respectively. The carnivorous fishSander lucioperca, andAbramis brama, an omnivorous fish, were allocated to the top of the food web in Ghrib and Harreza reservoirs, respectively. In the latter, a reservoir with low hydrodynamism and depth, the food web is simpler with a single fish species, which benefits from both benthic and pelagic sources. In Ghrib, a deeper dam with stronger hydrodynamics, only the riverine crabPotamon algerienseexploits the benthic sources, whereas fish mainly feed on zooplankton.