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8 páginas, 4 tablas, 2 figuras. ; Stable isotopes of carbon and nitrogen were used to assess the relevance of 4 primary carbon sources (the macroalga Cystoseira balearica, decaying blades of the seagrass Posidonia oceanica, seagrass epiphytes and pelagic particulate organic matter [POM]) for consumers inhabiting 3 adjoining subtidal habitats in the Western Mediterranean: seagrass meadows, unvegetated sandy patches and the overlying pelagic ecosystem. MANOVA and ANOVA revealed statistically significant differences between the δ 13C signal of decaying blades of P. oceanica (–13.0 ± 0.6‰), epiphytes (–19.7 ± 0.4‰) and a third group including POM (–23.1 ± 0.3‰) and C. balearica (–22.7 ± 0.8‰). However, these primary sources did not differ in their δ 15N signals (average: 1.0‰; range: 0.8 to 1.2‰). IsoSource mixing model software was used to calculate the contribution of each primary source to the carbon assimilated by each animal species. Nested ANOVA showed that the 3 trophic webs differed in the average contribution of the decaying blades of P. oceanica to the carbon assimilated by animals. The average contribution was 46.0 ± 14.0% for meadow-dwelling species, 18.3 ± 6.0% for sand-dwelling species and 12.8 ± 3.0% for pelagic species, once zooxanthellae-bearing jellyfish were removed from the analysis. However, IsoSource provided solutions for all the pelagic species and for half the sand-dwelling species that do not use decaying blades of P. oceanica as a carbon source. Conversely, IsoSource identified the decaying blades of P. oceanica as a relevant carbon source in all the solutions calculated for 3 different sand-dwelling species and in all of the meadowdwelling species. Thus, we conclude that organic detritus from P. oceanica is a relevant carbon source for species inhabiting seagrass meadows and for those sand-dwelling species living close to the meadows, but not for species exploiting deeper and more distant unvegetated patches. ; These samples were analyzed under the Life project 'Protección de Praderas de Posidonia en LICs de Baleares' LIFE 2000/NAT/E/7303 and the project BOS2003-05904 of the Spanish Government (CICYT). M. Sales was supported by Institut Menorquí d'Estudis ; Peer reviewed

Organochlorine (OC) pesticides and the more persistent polychlorinated biphenyls (PCBs) have well-established dose-dependent toxicities to birds, fish and mammals in experimental studies, but the actual impact of OC pollutants on European marine top predators remains unknown. Here we show that several cetacean species have very high mean blubber PCB concentrations likely to cause population declines and suppress population recovery. In a large pan-European meta-analysis of stranded (n = 929) or biopsied (n = 152) cetaceans, three out of four species:- striped dolphins (SDs), bottlenose dolphins (BNDs) and killer whales (KWs) had mean PCB levels that markedly exceeded all known marine mammal PCB toxicity thresholds. Some locations (e.g. western Mediterranean Sea, south-west Iberian Peninsula) are global PCB "hotspots" for marine mammals. Blubber PCB concentrations initially declined following a mid-1980s EU ban, but have since stabilised in UK harbour porpoises and SDs in the western Mediterranean Sea. Some small or declining populations of BNDs and KWs in the NE Atlantic were associated with low recruitment, consistent with PCB-induced reproductive toxicity. Despite regulations and mitigation measures to reduce PCB pollution, their biomagnification in marine food webs continues to cause severe impacts among cetacean top predators in European seas. ; The research was conducted by the UK Cetacean Strandings Investigation Program (CSIP) and the Centre for Environment, Fisheries and Aquaculture Science (Cefas) under contract to the UK Department for Environment, Food and Rural Affairs (Defra) and the Devolved Governments of Scotland and Wales. Additional funding for toxicological analyses was provided by ASCOBANS under contract "SSFA2010-3" and by the Fundació Barcelona Zoo. The Gulf of Cádiz and Strait of Gibraltar samples collection were sponsored by Loro Parque Foundation, Fundación Biodiversidad, CEPSA and ECOCET Project (CGL2011-25543) and logistical support for sample sexing was provided by Laboratorio de Ecología Molecular, Estación Biológica de Doñana, CSIC (LEM-EBD). Samples from Galicia were obtained with the support of Direccion Xeral de Conservacion da Natureza-Xunta de Galicia, co-financed with European Regional Development Funds (ERDF/FEDER). S. Murphy was supported by a Marie Curie International Outgoing Fellowship within the Seventh European Community Framework Programme. R. de Stephanis and J. Giménez were supported by the Severo Ochoa Programme for Centres of Excellence in R + D + I (SEV-2012-0262). A. D. Foote was supported by a Lawski Foundation stipend. ; Peer reviewed