Isotopic niche of coastal fish and cephalopods off the Campos Basin, southeastern Brazil

The stable isotopes of carbon (δ13C) and nitrogen (δ15N) of three demersal guilds (benthic feeders, benthic/nekton feeders and nekton feeders) were assessed to understand their trophic relationships on the southeastern Brazilian coast. The organic matter (OM) pool that fuels the demersal food web is composed of a mixture of autochthonous (marine) and allochthonous (terrigenous) sources, highlighting the Paraíba do Sul River (PSR) influence in the shallow coastal waters, regardless of seasonality. Of the studied guilds, the nekton feeder guild (Doryteuthis plei, Lophius gastrophysus, Percophis brasiliensis and Saurida caribbaea) in the demersal food web had the highest δ15N’ values in the dry and rainy seasons. The benthic feeder guild (Atlantoraja platana, Dactylopterus volitans, Dules auriga, Etropus longimanus, Prionotus nudigula and Zapteryx brevirostris) presented the widest isotopic niche breadth (highest total niche area and trophic diversity) due to the assimilation of a variety of benthic crustaceans, with different isotope signatures. The assimilation of benthic and pelagic crustaceans by the benthic feeder and benthic/nekton feeder (Atlantoraja cyclophora, Octopus vulgaris and Priacanthus arenatus) guilds resulted in isotopic overlap (28.1–50.6%). Seasonal trends from benthic and inshore to pelagic and offshore associated food webs were observed for the benthic feeder and benthic/nekton feeder guilds. Our results highlight the importance of terrestrial OM sources from PSR to shallow coastal demersal food webs off inner and medium continental shelf in southeastern Brazil. In addition, the trophic relationships of megafauna from benthic to nekton feeders were discussed.