Dead leaves of the Neptune grass, Posidonia oceanica (L.) Delile, in the Mediterranean coastal zone, are colonized by an abundant "detritivorous" invertebrate community that is heavily predated by fishes. This community was sampled in August 2011, November 2011, and March 2012 at two different sites in the Calvi Bay (Corsica). Ingested artificial fibers (AFs) of various sizes and colors were found in 27.6% of the digestive tracts of the nine dominant species regardless of their trophic level or taxon. No seasonal, spatial, size, or species-specific significant differences were revealed; suggesting that invertebrates ingest AFs at constant rates. Results showed that, in the gut contents of invertebrates, varying by trophic level, and across trophic levels, the overall ingestion of AFs was low (approximately 1 fiber per organism). Raman spectroscopy revealed that the ingested AFs were composed of viscose, an artificial, cellulose-based polymer. Most of these AFs also appeared to have been colored by industrial dyes. Two dyes were identified: Direct Blue 22 and Direct Red 28. The latter is known for being carcinogenic for vertebrates, potentially causing environmental problems for the P. oceanica litter community. Techniques such as Raman spectroscopy are necessary to investigate the particles composition, instead of relying on fragment size or color to identify the particles ingested by animals.

The shrimp Rimicaris exoculata dominates several hydrothermal vent ecosystems of the MidAtlantic Ridge and is thought to be a primary consumer harbouring a chemoautotrophic bacterial community in its gill chamber. The aim of the present study was to test current hypotheses concerning the epibiont's chemoautotrophy, and the mutualistic character of this association. Invivo experiments were carried out in a pressurised aquarium with isotope-labelled inorganic carbon (NaH 13 CO 3 and NaH 14 CO 3 ) in the presence of two different electron donors (Na 2 S 2 O 3 and Fe 2 þ ) and with radiolabelled organic compounds ( 14 C-acetate and 3 H-lysine) chosen as potential bacterial substrates and/or metabolic by-products in experiments mimicking transfer of small biomolecules from epibionts to host. The bacterial epibionts were found to assimilate inorganic carbon by chemoautotrophy, but many of them (thick filaments of epsilonproteobacteria) appeared versatile and able to switch between electron donors, including organic compounds (heterotrophic acetate and lysine uptake). At least some of them (thin filamentous gammaproteobacteria) also seem capable of internal energy storage that could supply chemosynthetic metabolism for hours under conditions of electron donor deprivation. As direct nutritional transfer from bacteria to host was detected, the association appears as true mutualism. Import of soluble bacterial products occurs by permeation across the gill chamber integument, rather than via the digestive tract. This first demonstration of such capabilities in a decapod crustacean supports the previously discarded hypothesis of transtegumental absorption of dissolved organic matter or carbon as a common nutritional pathway.

The aim of this work was to identify and compare, using nitrogen and carbon stable isotope data, the food sources supporting consumer communities in a Mediterranean seagrass bed (Gulf of Calvi, Corsica) with those in an adjacent epilithic alga-dominated community. Isotopic data for consumers are not significantly dierent in the two communities. Particulate matter and algal material (seagrass epi¯ora and dominant epilithic macroalgae) appear to be the main food sources in both communities. Generally, the d 13 C of animals suggests that the seagrass Posidonia oceanica (L.) Delile represents only a minor component of their diet or of the diet of their prey, but the occurrence of a mixed diet is not excluded. P. oceanica dominates the diet of only of few species, among which holothurians appear as key components in the cycling of seagrass material.

Effects of physiological processes such as gestation, lactation and nutritional stress on stable isotope ratios remain poorly understood. To determine their impact, we investigated these processes in simultaneously fasting and lactating northern elephant seals (Mirounga angustirostris). Stable carbon and nitrogen isotope values were measured in blood and milk of 10 mother-pup pairs on days 5 and 22 of lactation. As long-and short-term integrators of diet, blood cells and serum may reflect foraging data or energy reserves from late gestation and lactation, respectively. Limited changes in isotopic signatures of maternal blood over the lactating period were highlighted. Nitrogen isotope fractionation associated with mother-to-offspring 1 2 MARINE MAMMAL SCIENCE, VOL. **, NO. **, 2010 transfer of nutrients was generated between mother and offspring during gestation and lactation. This fractionation was tissue and time-specific, it varied between early and late lactation from +0.6 to +1.3 in blood cells and from +1.1 to nonsignificant value in serum. Therefore, if pups appear to be good proxies to investigate the female trophic ecology especially for C sources, much more caution is required in using ␦ 15 N values. Further studies are also needed to better define the relative impact of fasting and lactation on the enrichment or depletion of isotopes in different tissues.Key words: northern elephant seal, Mirounga angustirostris, stable isotopes, lactation, fasting, gestation.Stable carbon and nitrogen isotope ratios ( 13 C/ 12 C reported as ␦ 13 C and 15 N/ 14 N reported as ␦ 15 N, respectively) in animal tissues have been widely used to study trophic relationships and foraging locations in terrestrial and marine food webs (Hobson and Stirling 1997, Burns et al. 1998, Burton and Koch 1999, Kelly 2000, Kurle and Worthy 2001, Das et al. 2003, Dehn et al. 2007. Isotopic ratios in the various foods consumed are reflected in the animal's tissues, proportionate to the amount assimilated for each food source, after accounting for fractionation against heavier isotopes in the digestion and assimilation process Epstein 1978, 1981). Stable nitrogen isotopes undergo fractionation between predator and prey, leading to an enrichment in 15 N with increasing trophic level Epstein 1981, Minagawa andWada 1984), thereby denoting an animal's trophic position. The ␦ 13 C value is close to that of the diet and is used to indicate relative contributions to the diet of two different potential primary sources in a trophic network, indicating for example the aquatic vs. terrestrial, inshore vs. offshore, or pelagic vs. benthic contribution to food intake (Hobson et al. 1995, Dauby et al. 1998. Geographic differences in ␦ 13 C values can be used to indicate foraging locations of animals in marine environments (Kelly 2000, Kurle andWorthy 2002). Stable isotope methodology, however, is dependent on physiological and biochemical assumptions that are not sufficiently taken into consideration (Cherel et al. 2005). Indeed, nutritional st...

Associations of tunas and dolphins in the wild are quite frequent events and the question arises how predators requiring similar diet in the same habitat share their environmental resources. As isotopic composition of an animal is related to that of its preys, stable isotope ( 13 C/ 12 C and 15 N/ 14 N) analyses were performed in three predator species from the North-east Atlantic: the striped dolphin, Stenella coeruleoalba, the common dolphin Delphinus delphis and the albacore tuna, Thunnus alalunga, and compared to their previously described stomach content. Heavy metals (Cd, Zn, Cu and Fe) are mainly transferred through the diet and so, have been determined in the tissues of the animals. Tuna muscles display higher d 15 N than in common and striped dolphins (mean: 11.4 vs. 10.3½ and 10.4½, respectively) which re¯ects their higher trophic level nutrition. Higher d 13 C are found in common ()18.4½) and striped dolphin ()18.1½) muscles than in albacore tuna ()19.3½) probably in relation with its migratory pattern. The most striking feature is the presence of two levels of cadmium concentrations in the livers of the tunas (32 mg kg À1 dry weight (DW) vs. 5 mg kg À1 DW). These two groups also di er by their iron concentrations and their d 15 N and d 13 C liver values. These results suggest that in the Biscay Bay, tunas occupy two di erent ecological niches probably based on di erent squid inputs in their diet. Ó