Résumé: We analyzed stomach contents and muscle isotopic composition (delta C-13, delta N-15) of yellowstripe goatfish Mulloidichthys flavolineatus from a coral reef to investigate size-related dietary changes and resource or habitat partitioning. Juveniles (< 12 cm total length [TL]), young adults (12 <= TL < 17 cm) and adults (>= 17 cm TL) showed a high diet overlap, especially between juveniles and young adults. According to stomach contents analysis, M. flavolineatus widens its prey spectrum with increasing size from a common prey pool that includes polychaetes, tanaids and harpacticoid copepods. We observed a significant increase in delta C-13 values (from -17.1 +/- 0.5 parts per thousand for juveniles to -10.7 +/- 0.8 parts per thousand for adults), which were correlated to fish size. Adults (delta N-15 mean of 11.1 +/- 1.8 parts per thousand) were one trophic level above juveniles and young adults (7.7 +/- 0.5 and 7.4 +/- 0.5 parts per thousand, respectively). These patterns of isotopic changes confirmed ontogenetic dietary shifts. However, trophodynamics can be influenced by physiological factors such as growth and sexual maturity. M flavolineatus shift from a pelagic to a macrobenthic diet, which is equilibrated at the adult stage. Results from combined stomach contents (prey volume) and stable isotope analyses suggested a dominant contribution of polychaetes (macrofauna), possibly through selective feeding. Conversely, on the basis of prey volume and stable isotope data, meiofauna did not feature significantly in the diet despite their high abundance in stomachs. Two adult groups were distinguished based on their delta N-15 values (11.9 +/- 0.8 and 7.8 +/- 0.6 parts per thousand), indicating possible stage-specific partitioning in habitat use inside the reef.

Résumé: The study of the feeding ecology of marine organisms is crucial to understanding their ecological roles and advancing our knowledge of marine ecosystem functioning. The aim of this study was to analyse the trophic ecology of two demersal predator species, black anglerfish (Lophius budegassa) and white anglerfish (L. piscatorius), in the northwestern Mediterranean Sea. Both species are important in the study area due to their high abundance and economic value, but information about their feeding behaviour is scarce. Here, we described the diet composition and ecological role of these two species, investigating whether trophic segregation exists between them and amongst fish of different sizes. In addition, by using experimental survey data we described the spatial distribution of both species to help us interpret trophic behaviour patterns. We gathered samples of two different sizes (small individuals of a total length <30 cm and large individuals >= 30 cm) of both species and combined stomach content analyses (SCA) and stable isotope analyses (SIA) of nitrogen and carbon with isotopic mixing models. Our results revealed that both anglerfish species are opportunistic predators, showing a diet composed mainly of fishes and, to a lesser extent, of crustaceans, with a small proportion of cephalopods, gastropods, bivalves and echinoderms. We found trophic segregation between the two species and the two sizes, indicating that they feed on different prey, in line with differences in their spatial distribution within the study area. This partial partition of food resources could also be explained by the differences in rhythms of activity that were reported in previous studies. In addition, although both species occupied a high position within the food web, our results showed that white anglerfish individuals and the large-sized fish of both species held higher trophic positions. This study demonstrates the usefulness of complementary approaches for trophic studies and confirms that both anglerfish species play an important role as predators in the northwestern Mediterranean Sea food web. (C) 2016 Elsevier Ltd. All rights reserved.

Résumé: The La Perouse seamount (60 m depth) has so far been poorly studied despite it being a short distance (160 km) from Reunion Island. As part of the MADRidge project, a multidisciplinary cruise was conducted to evaluate the effect of this shallow seamount on the local hydrology and ecology. Current measurements, temperature and chlorophyll-a profiles, and mesozooplankton and micronekton samples were collected between the summit and 35 km away. Micronekton data were supplemented with stomach content of pelagic top predators as well as fisheries statistics from the domestic longline fleet operating from Reunion. Vertical current profiles revealed distinct patterns between the offshore and seamount-flanked stations, giving evidence of topographical induced flow instabilities, notably on its leeward side (west) relative to the east flank. Distinct patterns in temperature and chlorophyll-a vertical profiles suggest the formation of convergent and divergent circulation cells as a result of the irregular and crescent-like summit topography. Spatial differences in zooplankton abundance were detected with higher biovolumes on the leeward flank. The overall acoustic backscatter for micronekton over the summit was weaker than offshore, but highly concentrated in the upper layer. Albacore tuna and swordfish dominate the longline catch west of Reunion, seemingly in association with a deep (900 m) topographic feature. Yet the largest catch is not directly associated with La Perouse which would be too shallow for top predators to aggregate around in the long term. Enhanced levels of phytoplankton or zooplankton enrichment at La Perouse were not demonstrated in this study, nor was there notable diversity of micronekton species. This might explain the relatively limited importance of this seamount to the tuna fisheries in this region.