Trophic ecology of atlantic bluefin tuna (Thunnusthynnus) larvae from the gulf of Mexico and nw mediterranean spawning grounds: A comparative stable isotope study

Abstract

The present study uses stable isotopes of nitrogen and carbon (λ15Nandλ13C) as trophic indicators for Atlantic bluefin tuna larvae (BFT) (6-10mm standard length) in the highly contrasting environmental conditions of the Gulf of Mexico (GOM) and the Balearic Sea (MED). These regions are differentiated by their temperature regime and relative productivity, with the GOM being significantly warmer and more productive. MED BFT larvae showed the highest λ15N signatures, implying an elevated trophic position above the underlyingmicrozooplankton baseline. Ontogenetic dietary shifts were observed in the BFT larvae from the GOM and MED which indicates early life trophodynamics differences between these spawning habitats. Significant trophic differences between the GOM and MED larvae were observed in relation to λ15N signatures in favour of the MED larvae, which may have important implications in their growth during their early life stages.These low λ15N levels in the zooplankton from the GOM may be an indication of a shifting isotopic baseline in pelagic food webs due to diatrophic inputs by cyanobacteria. Lack of enrichment for λ15N in BFT larvae compared to zooplankton implies an alternative grazing pathway from the traditional food chain of phytoplankton zooplanktonlarval fish. Results provide insight for a comparative characterization of the trophic pathways variability of the two main spawning grounds for BFT larvae.