Littoral macrophyte assemblage determines the δ13C signal of pelagic food web in shallow eutrophic temperate lakes from the pampa plain

GONZALEZ SAGRARIO MA; RODRÍGUEZ GOLPE, D.; LA SALA, L.; SÁNCHEZ VUICHARD, G.; PANARELLO, H.

La Plata

Congreso; VI Congreso Argentino de Limnología, Agua, Ambiente y Sociedad; 2014

ILPLA, CONICET, FAC CIENCIAS Y MUSEO UNLP

The study clarifies the relevance of the trophic linkage between the littoral and pelagic food webs mediated by the type of littoral vegetation in shallow eutrophic lakes. For this purpose, we coupled carbon and nitrogen isotopic analyses with conventional fish gut analyses to predict the degree of linkage and dependence between the littoral and pelagic systems. Carbon and nitrogen stable isotopes were determined in benthic, pelagic and littoral fish, macroinvertebrates, zooplankton, seston, periphyton, macrophytes and dissolved inorganic carbon in three shallow temperate lakes from the Pampa plain (Argentina, South America). The δ13C signals of seston differed among lakes, representing the planktonic or the phytoplankton plus littoral detritus signal. Macroinvertebrates exhibited a more enriched carbon signature in the lake codominated by emergent and submerged vegetation than in lakes dominated by emergent vegetation. Fish carbon signatures were intermediate between littoral- and pelagic-carbon signatures in all the lakes. More than the 80% of the carbon that sustain adult Oligosarcus, Odontesthes and Rhamdia is channeled from littoral resources and more than the 90% of the carbon consumed by Cyphocharax voga from the benthic habitat. Our results demonstrate that sources of littoral carbon (macrophytes and periphyton) are relevant and sustain both, the littoral and the pelagic food webs in these shallow temperate lakes. In fact,the δ13C-seston was related to the type of macrophyte (submerged or emergent) dominant in each system and also to lake size. Moreover, littoral carbon scale up food webs supporting directly or indirectly fish biomass. Littoral carbon must enter directly in the pelagic compartment as plant detritus which is firstly incorporated by zooplankton. Fish, both littoral and pelagic species, incorporate littoral carbon directly or indirectly through the consumption of littoral or pelagic prey that are supported by littoral producers. In conclusion, littoral primary producer signal scaled up to fish, resulting in a coupling of the pelagic and littoral compartments.