Trophic Ecology of Atlantic Bluefin Tuna (Thunnus thynnus) Larvae from the Gulf of Mexico and NW Mediterranean Spawning Grounds: A Comparative Stable Isotope Study

The present study uses stable isotopes of nitrogen and carbon (δ15Nandδ13C) 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 δ15N 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 δ15N signatures in favour of the MED larvae, which may have important implications in their growth during their early life stages. These low δ15N 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 δ15N in BFT larvae compared to zooplankton implies an alternative grazing pathway from the traditional food chain of phytoplankton— zooplankton—larval fish. Results provide insight for a comparative characterization of the trophic pathways variability of the two main spawning grounds for BFT larvaeVersión del editor4,411

Ontogenetic and seasonal changes in the feeding habits and trophic levels of two small pelagic fish species

13 pages, 5 figures, 3 tablesWe investigated ontogenetic and seasonal changes in the feeding ecology of 2 small pelagic fish species, the European anchovy Engraulis encrasicolus and the European pilchard Sardina pilchardus in the Gulf of Lions (NW Mediterranean). By analysing the stable isotopes δ13C and δ15N, we determined the seasonal variation in the food sources and in the trophic level of these species, and we examined dietary shifts during development. The results of these investigations provided estimates of the diets of both species. We compared the values observed during different seasons (summer, autumn and winter) and at different developmental stages (late-larvae, juveniles and adults) for both species, together with the values of potential groups of prey (microplankton, cladocerans, copepods and appendicularians). Late-larvae preferred to feed on microplankton, although differences in the diet appeared after metamorphosis. Cladocerans were usually the preferred prey when available (summer), and appendicularians were the preferred prey in autumn. During the winter, the diets seemed to be more heterogeneous. Different feeding behaviours between the late-larvae of the 2 species were the most likely reason for the slightly different trophic levels found in the present study. This research demonstrates that studies with stable isotopes can furnish an alternative and/or complementary method for determining the diet of small pelagic fishes over extended periods and provides comprehensive knowledge of the functioning of the pelagic ecosystemD.C. was funded by a PhD contract within the European project SARDONE (FP6 - 44294). J.N. was supported by a postdoctoral contract of the Juan de la Cierva programme (MICINN-JDC, Spanish Ministry of Science and Innovation)Peer reviewe

Mesograzers in Posidonia oceanica meadows: an update of data on gastropod-epiphyte-seagrass interactions

9 páginas, 5 tablas, 7 figuras.Information on dietary habits of mesograzers in Posidonia oceanica seagrass meadows is scarce and restricted to a few species. Here we provide data on the most likely food sources for eight gastropod species inferred from stable isotope data. We observed very similar isotopic signals for all species regardless of trophic guild category, indicating similar consumption behaviour with a main diet contribution from epiphytes. We also review the state of knowledge on gastropod-epiphyte-seagrass interactions, with particular emphasis on the scarcity of studies derived from Mediterranean systems. Laboratory experiments showed that under moderately nutrient-enriched conditions, two species of gastropods (Bittium reticulatum and Jujubinus striatus) were controlling epiphyte biomass at high grazer densities, with no consequences for seagrass performance. Finally, the results of a long-term in situ fertilisation experiment showed that the δ15N signal for seagrass, epiphytes and gastropods reflects experimentally induced eutrophication, thus cascading up nutrient effects throughout the food web.This work was supported by the FUNPOS project (Plan Nacional IqD, MEC ref. 2006301006). David Costalago was funded by MEC under the I3P postgrado programme and Diana Piorno is the recipient of a La Caixa pre-doctoral fellowship (2006–2008).Peer reviewe

Comparación de la dieta de juveniles de anchoa Engraulis encrasicolus y sardina Sardina pilchardus del Golfo de León en distintas épocas del año

Trabajo presentado en el XVI Simposio Ibérico de Estudios de Biología Marina (SIEBM), celebrado en Alicante (España), del 6 al 10 de septiembre de 201

Comparison of the feeding apparatus and diet of European sardines Sardina pilchardus of Atlantic and Mediterranean waters: ecological implications

15 pages, 4 figures, 3 tablesIn this study, the feeding apparatus (gill rakers, GR) and the diet composition of European sardine Sardina pilchardus populations living in two contrasting environments were compared: the upwelling area off western Iberia and the comparatively less productive region of the north-western Mediterranean Sea. The importance of local adaptations in the trophic ecology of this species was estimated. Sardina pilchardus from the Atlantic Iberian coast and from the north-western Mediterranean Sea have clear differences in the feeding apparatus and diet compositions. Those from the Atlantic Iberian coast have significantly more GRs than S. pilchardus of the same size range in the Mediterranean Sea. While S. pilchardus from the Mediterranean Sea mostly depend on prey ranging between 750-1500 and 3000-4000μm, corresponding mostly to cladocerans, decapods and copepods, those from the Atlantic depend on smaller prey (50-500 and 1000-1500μm) that include phytoplankton and copepods, particularly during summer months, and S. pilchardus eggs during the winter. The marked difference between the trophic ecology of S. pilchardus in the two areas studied appears to have originated from different dietary strategies that the two populations have adopted in contrasting feeding environments. These differences are shown to profoundly affect the size and quality of prey consumed, and the effect of cannibalism on the populations. © 2015 The Fisheries Society of the British IslesPeer Reviewe

Seasonal comparison of the diets of juvenile European anchovy Engraulis encrasicolus and sardine Sardina pilchardus in the Gulf of Lions

9 pages, 4 figures, 4 tablesAnchovy and sardine in the Mediterranean are known to share the same habitat and, consequently, to interact with one another. These two sympatric pelagic species are planktivorous and consume a wide range of planktonic prey items during all their developmental stages, potentially overlapping their ecological niches, although the feeding interactions between these species have been poorly investigated. Here we compare the dietary habits of the juvenile phases of anchovy and sardine during different seasons in the northwestern Mediterranean Sea, through analysis of their stomach contents and of their feeding-related anatomical characteristics. In this study we show that juveniles of anchovy and sardine do not compete for food, and we describe significant dietary differences between anchovy and sardine due to their different alimentary tract morphology. © 2014 Elsevier B.V.This researchwas conductedwithin the European project SARDONE (FP6 – 44294)Peer Reviewe

Growth and nutritional condition of anchovy larvae on the west and southeast coasts of South Africa

Cape anchovy Engraulis encrasicolus is an ecologically and economically important pelagic fish species occurring along the coast of South Africa. A recent eastward shift in Cape anchovy distribution indicates that environmental conditions are becoming more favorable for the species on the east coast. This shift is particularly important in the sheltered Algoa Bay region, a nursery area for fish larvae. However, the relatively low productivity of the Agulhas Current Large Marine Ecosystem on the eastern coast of South Africa may result in an anchovy population in poorer nutritional condition and with slower growth rates than the west coast population. Using otolith and nucleic acid analyses, the growth rates of anchovy larvae from the western and southeastern coasts of South Africa were compared. The otolith analysis results indicated that, at any given age, individual growth rates for anchovy larvae were higher on the southeast coast than on the west coast. The RNA:DNA values also indicated that instantaneous growth rates of anchovy larvae were higher in Algoa Bay than on the west coast. At the time of sampling, chlorophyll and zooplankton productivity were higher at sampling sites in Algoa Bay than sites on the west coast, potentially due to favorable oceanographic features in the bay. As such, the results suggest that Algoa Bay is a suitable and potentially favorable nursery area for the early stages of anchovy, highlighting the importance of separate management of the southeast coast region in a changing world.</jats:p