de Figueiredo G. G. A. A. auteur aut IRD Schwamborn R. auteur aut IRD Bertrand Arnaud auteur aut IRD Munaron Jean-Marie auteur aut IRD Le Loc'h François auteur aut IRD text journalArticle eng text/pdf born digital access 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. specialized Plankton delta C-13 delta N-15 Size classes Trophic level Predator/prey mass ratio ATLANTIQUE BRESIL FERNANDO DE NORONHA ROCAS ATOLL ZONE TROPICALE 036 034 212 103449 [10 p.] 2020 0924-7963 https://www.documentation.ird.fr/hor/fdi:010079900 10.1016/j.jmarsys.2020.103449 0924-7963 [F B010079900] https://www.documentation.ird.fr/hor/fdi:010079900 https://www.documentation.ird.fr/intranet/publi/2020/11/010079900.pdf Accès réservé (Intranet de l'IRD) IRD - Base Horizon / Pleins textes 2020-12-08 2025-02-24 fdi:010079900 fre