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Liess, A., Faithfull, C., Reichstein, B., Rowe, O., Guo, J., Pete, R., et al. (2015). Terrestrial runoff may reduce microbenthic net community productivity by increasing turbidity: a Mediterranean coastal lagoon mesocosm experiment. Hydrobiologia, 753(1), 205–218.
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Zudaire, I., Murua, H., Grande, M., Goñi, N., Potier, M., Ménard, F., et al. (2015). Variations in the diet and stable isotope ratios during the ovarian development of female yellowfin tuna (Thunnus albacares) in the Western Indian Ocean. Mar Biol, 162(12), 2363–2377.
Résumé: The feeding strategy of female yellowfin tuna (Thunnus albacares) during their reproductive cycle was investigated using a combination of different trophic tracers, i.e., stomach contents and dual stable isotope analysis, along with an assessment of ovarian development based on a histological analysis. To complete these analyses, we collected 215 female yellowfin from the Western Indian Ocean in 2009 and 2010. From these fish, we noted the ovarian development and analyzed the contents of 166 non-empty stomachs and 104 liver and muscle tissue samples. Stomach content analysis identified a large variety of prey species (45 prey families), key groups including crustaceans dominated by the swimming crab Charybdis smithii and crustacean larvae; fish dominated by the cigarfish Cubiceps pauciradiatus; and cephalopods dominated by ommastrephids Sthenoteuthis oualaniensis and Ornithoteuthis volatilis. Individuals capable of spawning appeared to feed intensively, particularly on cigarfish, during the reproductive period. From the mean reconstituted weight values of the preys, our results indicated that this intensive feeding led to increased amounts of acquired energy. The results of the stable isotope analyses, carried out on the muscle and liver tissues, indicated a clear decrease in values from north to south. These analyses also showed that liver δ15N values in spawning females were significantly lower than those in immature and developing individuals. This latter observation highlights the differences in metabolic processes that occur between tissues during ovarian development and underlines the importance of the liver in energy acquisition and mobilization in female yellowfin tuna during reproduction.
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Navarro, J., López, L., Coll, M., Barría, C., & Sáez-Liante, R. (2014). Short- and long-term importance of small sharks in the diet of the rare deep-sea shark Dalatias licha. Mar Biol, 161(7), 1697–1707.
Résumé: Knowing the trophic ecology of marine predators is essential to develop an understanding of their ecological role in ecosystems. Research conducted on deep-sea and threatened shark species is limited. Here, by combining analyses of individual stomach contents and stable isotope values, we examined the trophic ecology (dietary composition and trophic position) of the kitefin shark Dalatias licha, a deep-sea shark considered as near threatened globally and as data deficient in the Mediterranean Sea. Results revealed the importance of small sharks in the diet of the kitefin shark at short- and long-term scales, although fin-fish, crustaceans and cephalopods were also found. Predation on sharks reveals the high trophic position of the kitefin shark within the food web of the western Mediterranean Sea. Stable isotope values from liver and muscle tissues confirmed our results from stomach content analysis and the high trophic position.
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Ben Gharbia, H., Yahia, O. K. - D., Cecchi, P., Masseret, E., Amzil, Z., Herve, F., et al. (2017). New insights on the species-specific allelopathic interactions between macrophytes and marine HAB dinoflagellates. Plos One, 12(11), e0187963.
Résumé: Macrophytes are known to release allelochemicals that have the ability to inhibit the proliferation of their competitors. Here, we investigated the effects of the fresh leaves of two magnoliophytes (Zostera noltei and Cymodocea nodosa) and thalli of the macroalgae Ulva rigida on three HAB-forming benthic dinoflagellates (Ostreopsis cf. ovata, Prorocentrum lima, and Coolia monotis). The effects of C. nodosa and U. rigida were also tested against the neurotoxic planktonic dinoflagellate Alexandrium pacificum Litaker sp. nov (former Alexandrium catenella). Co-culture experiments were conducted under controlled laboratory conditions and potential allelopathic effects of the macrophytes on the growth, photosynthesis and toxin production of the targeted dinoflagellates were evaluated. Results showed that U. rigida had the strongest algicidal effect and that the planktonic A. pacificum was the most vulnerable species. Benthic dinoflagellates seemed more tolerant to potential allelochemicals produced by macrophytes. Depending on the dinoflagellate/macrophyte pairs and the weight of leaves/thalli tested, the studied physiological processes were moderately to heavily altered. Our results suggest that the allelopathic activity of the macrophytes could influence the development of HAB species.
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Dhurmeea, Z., Zudaire, I., Chassot, E., Cedras, M., Nikolic, N., Bourjea, J., et al. (2016). Reproductive Biology of Albacore Tuna (Thunnus alalunga) in the Western Indian Ocean. Plos One, 11(12), e0168605.
Résumé: The reproductive biology of albacore tuna, Thunnus alalunga, in the western Indian Ocean was examined through analysis of the sex ratio, spawning season, length-at-maturity (L50), spawning frequency and fecundity. From 2013 to 2015, a total of 923 female and 867 male albacore were sampled. A bias in sex ratio was found in favor of females with fork length (LF) < 100 cm. Using histological analyses and gonadosomatic index, spawning was found to occur between 10°S and 30°S, mainly to the east of Madagascar from October to January. Large females contributed more to reproduction through their longer spawning period compared to small individuals. The L50 (mean ± standard error) of female albacore was estimated at 85.3 ± 0.7 cm LF. Albacore spawn on average every 2.2 days within the spawning region and spawning months, from November to January. Batch fecundity ranged between 0.26 and 2.09 million oocytes and the relative batch fecundity (mean ± standard deviation) was estimated at 53.4 ± 23.2 oocytes g-1 of somatic-gutted weight. The study provides new information on the reproductive development and classification of albacore in the western Indian Ocean. The reproductive parameters will reduce uncertainty in current stock assessment models which will eventually assist the fishery to be sustainable for future generations.
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