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Albo-Puigserver, M., Navarro, J., Coll, M., Aguzzi, J., Cardona, L., & Saez-Liante, R. (2015). Feeding ecology and trophic position of three sympatric demersal chondrichthyans in the northwestern Mediterranean. Mar. Ecol.-Prog. Ser., 524, 255–268.
Résumé: Understanding how marine predators interact is a scientific challenge. In marine ecosystems, segregation in feeding habits has been largely described as a common mechanism to allow the coexistence of several competing marine predators. However, little is known about the feeding ecology of most species of chondrichthyans, which play a pivotal role in the structure of marine food webs worldwide. In this study, we examined the trophic ecology of 3 relatively abundant chondrichthyans coexisting in the Mediterranean Sea: the blackmouth catshark Galeus melastomus, the velvet belly lanternshark Etmopterus spinax and the rabbit fish Chimaera monstrosa. To examine their trophic ecology and interspecific differences in food habits, we combined the analysis of stomach content and stable isotopes. Our results highlighted a trophic segregation between C. monstrosa and the other 2 species. G. melastomus showed a diet composed mainly of cephalopods, while E. spinax preyed mainly on shrimps and C. monstrosa on crabs. Interspecific differences in the trophic niche were likely due to different feeding capabilities and body size. Each species showed different isotopic niche space and trophic level. Specifically, C. monstrosa showed a higher trophic level than E. spinax and G. melastomus. The high trophic levels of the 3 species highlighted their important role as predators in the marine food web. Our results illustrate the utility of using complementary approaches that provide information about the feeding behaviour at short (stomach content) and long-term scales (stable isotopes), which could allow more efficient monitoring of marine food-web changes in the study area.
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Albo-Puigserver, M., Navarro, J., Coll, M., Layman, C. A., & Palomera, I. (2016). Trophic structure of pelagic species in the northwestern Mediterranean Sea. J. Appl. Dev. Psychol., 47, 27–35.
Résumé: Ecological knowledge of food web interactions within pelagic marine communities is often limited, impairing our capabilities to manage these ecologically and economically important marine fish species. Here we used stable isotope analyses to investigate trophic interactions in the pelagic ecosystem of the northwestern Mediterranean Sea during 2012 and 2013. Our results suggest that European sardine, Sardina pilchardus, and anchovy, Engraulis encrasicolus, are consumers located at relatively low levels of the pelagic food web. Unexpectedly, the round sardinella, Sardinella aurita, appeared to be located at a higher trophic level than the other small pelagic fish species, although previous studies found similarity in their diets. Isotope data suggested that trophic niches of species within the genera Trachurus spp. and Scomber spp., were distinct. Atlantic bonito Sarda sarda, European hake Merluccius merluccius and European squid Loligo vulgaris, appeared to feed at higher trophic levels than other species. Despite some intraspecific seasonal variability for some species, community trophic structure appeared relatively stable through the year. These data provide an important step for developing models of food web dynamics in the northwestern Mediterranean Sea. (C) 2016 Elsevier B.V. All rights reserved.
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Albouy, C., Velez, L., Coll, M., Colloca, F., Le Loc'h, F., Mouillot, D., et al. (2014). From projected species distribution to food-web structure under climate change. Global Change Biology, 20(3), 730–741.
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Annasawmy, P., Cherel, Y., Romanov, E., Le Loc'h, F., Menard, F., Ternon, J. - F., et al. (2020). Stable isotope patterns of mesopelagic communities over two shallow seamounts of the south-western Indian Ocean. Deep-Sea Res. Part II-Top. Stud. Oceanogr., 176, 104804.
Résumé: The stable carbon (delta C-13) and nitrogen (delta N-15) isotope values of soft tissues of micronekton (crustaceans, squid, mesopelagic fish) and zooplankton were measured from organisms collected on the RV Antea at two seamounts located in the south-western Indian Ocean: La Perouse (summit depth similar to 60 m) and “MAD-Ridge” (thus named in this study; summit depth similar to 240 m). Surface particulate organic matter (POM-Surf) showed higher delta C-13 at the more productive MAD-Ridge than at the oligotrophic La Perouse seamount. Particulate organic matter and zooplankton were depleted in N-15 at La Pemuse pinnacle compared with MAD-Ridge. Gelatinous organisms and crustaceans occupied the lowest and intermediate tmphic levels (TL similar to 2 and 3 respectively) at both seamounts. Mesopelagic fish and smaller-sized squid sampled at both seamounts occupied TL similar to 3 to 4, whereas the large nektonic squid, Ommastrephes bartramii, collected at MAD-Ridge only, exhibited a TL of similar to 5. The delta N-15 values of common open-water mesopelagic taxa were strongly influenced by specimen size and feeding habits at both seamounts, with an increase in delta N-15 values with increasing size. Carnivorous fish species sampled exclusively over the seamounts' flanks and summits exhibited TL values of similar to 4, irrespective of their wide size ranges. The work could not demonstrate any differences in delta C-13 values of mesopelagic fish between the seamounts and the surrounding oceanic areas. The study segregated clusters of mesopelagic organisms according to their delta C-13 and delta N-15 values, with variations in stable isotope values reflecting a complex range of processes possibly linked to productivity as well as biological and ecological traits of the species (size and feeding mode).
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Araújo Abrantes de Figueiredo, G. G., Schwamborn, R., Bertrand, A., Munaron, J. - M., & Le Loc'h, F. (2020). Body size and stable isotope composition of zooplankton in the western tropical Atlantic. J. Mar. Syst., 212, 103449.
Résumé: Size-based approaches are paramount tools for the study of marine food webs. Here, we investigated the relationship between zooplankton body size, stable isotope composition and trophic level (TL) along a large-scale onshore-offshore gradient in the western tropical Atlantic. Samples were obtained on the Brazilian continental shelf, slope and in oceanic waters (off Fernando de Noronha archipelago and Rocas Atoll) in September and October 2015. Zooplankton was sieved into five size fractions. Zooplankton was dominated by copepods, except for the largest (> 2000 mu m) size fraction, that showed a high biovolume of chaetognaths, decapods, and fish larvae. Maximum zooplankton abundance and biovolume was found at the continental slope. POM showed consistently lower delta C-13 than zooplankton, indicating a selective use of C-13-rich primary food sources by zooplankton. Particulate organic matter (POM) was more C-13-enriched in shelf areas (average: -22.8, -23.6 and -24.3% at the shelf, slope and oceanic islands, respectively), probably due to the higher abundance of diatoms nearshore. POM had delta N-15 values between 2.5 and 6.9% (average: 4.0, 4.9 and 4.2% at the shelf, slope and oceanic islands, respectively). Zooplankton delta N-15 and TL increased with body size. The delta N-15 of the 200-500 mu m size fraction was used as baseline for TL estimation. Oceanic areas (average baseline delta N-15 = 5.8% +/- 0.52, n = 14) showed a higher baseline delta N-15 than the shelf (average = 3.9% +/- 0.69, n = 9) and the slope areas (average = 3.1% +/- 0.93, n = 9). In spite of differing baselines, the delta N-15 data produced a consistent pattern of log-linear increase in TL with increasing size, in all areas. The choice of input trophic enrichment factor (TEF) values only slightly changed the log10 (body size) vs TL slopes, but this choice had a considerable effect on the estimates of predator/prey size ratio (PPSR) and predator/prey mass ratio (PPMR). Using a TEF above 2.3 leads to unrealistic PPSR and PPMR estimates. Overall average slope was 0.59 +/- 0.08 TL mu m(-1) with TEF = 2.3 and 0.42 +/- 0.07 TL mu m(-1) with TEF = 3.2.
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