Análisis de la alimentación de larvas y juveniles del “stock” patagónico de la merluza común (Merluccius hubbsi) en relación con la composición taxonómica, abundancia y calidad nutricional del zooplancton.
The trophic relationships among early life stages (larvae and age-0 juveniles) of Patagonian hake (Merluccius hubbsi) stock and the zooplanktonic community in the spawning (between Isla Escondida and Bahía Camarones) and nursery (Golfo San Jorge) areas in the Argentine Sea (SW Atlantic ocean) were investigated. The study took place in the north Patagonian region (42°-47° S) during hake reproductive season (December-March). The effect of environmental features, including frontal regions, upon results was analyzed. On the one hand, patterns of distribution, abundance and diversity of the zooplanktonic community were studied, as well as the nutritional quality of species that are prey for hake early stages. Besides, trophic ecology analyses of larvae and age-0 juveniles combined both traditional gut content analysis and the ‘fatty acid trophic markers’ approach. Both diet composition and feeding strategy of early stages were identified as well as their nutritional condition. This Thesis is the first work employing both approaches to study the trophic ecology of a very important fish species in the Argentine Sea. In the spawning area, the combined use of 67 and 300 um meshes allowed capturing the complete zooplanktonic size spectrum. The zooplanktonic community was dominated by small-sized calanoid copepods (< 1 mm), mainly eggs, nauplius larvae and copepodites, with Drepanopus forcipatus , Ctenocalanus vanus , Microsetella norvegica and Oithona helgolandica as key species. Abundances were higher in the traditional spawning sector (Isla Escondida, ~ 50 m depth) than in external waters (~ 100 m depth), strongly influenced by the presence of the North Patagonian frontal system (SFNP). Hake larvae were, at a population level, specialist predators upon calanoid copepods < 2 mm, showing a narrow trophic niche. In the nursery area, the zooplanktonic community was dominated by calanoid copepodites 1-2 mm in size. Maximum abundances occurred in the north and south extremes of the gulf, highly influenced by the presence of SFNP and San Jorge Gulf Frontal System, respectively. Age-0 juveniles had an almost exclusively pelagic diet represented mainly by the amphipod Themisto gaudichaudii and the euphausiid Euphausia lucens , showing a specialization at a population level towards both crustaceans. Epibenthic prey were only included in the diet of individuals > 110 mm. Thus, development of a permanent demersal habit would occur gradually at sizes between ~110-150 mm. Lipids and fatty acids were used, for the first time in the Argentine Sea, as indices of early stages nutritional condition as well as indicators of food items quality. Hake early stages and their prey tissues were characterized by palmitic, estearic, oleic, erucic and DHA fatty acids. Oleic acid identified carnivory as the main strategy for both stages, with erucic acid indicating larval consumption of calanoid copepods and palmitic acid evidencing age-0 juvenile predation upon amphipods and euphausiids. These markers validated the gut content analysis and detected assimilated prey items with low frequency of occurrence in the stomachs. Larvae and age-0 juveniles would be obtaining the essential fatty acids directly from their diets rather than from de novo synthesis, highlighting their great dependence upon the trophic environment. Moreover, fatty acids markers of bacteria and dinoflagellates both in hake stages and their prey tissues suggest a great contribution of the microbial pathway in the north Patagonian food web. In terms of energy density and essential fatty acids, prey would exhibit an adequate nutritional quality that would provide hake larvae and age-0 juveniles with a good nutritional condition. In the nursery area, condition was higher in frontal areas, while this was not observed in the spawning area. However, in the latter, result should be interpreted cautiously due to their preliminary fashion and the low number of samples available for the analyses. Results of this Thesis contribute to the knowledge of hake early life stages biology, assuming that their relationships with the trophic environment may affect recruitment of the species.
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| Format: | Thesis/Dissertation biblioteca |
| Language: | Spanish / Castilian |
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Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales
2015
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| Subjects: | Efectivos, Larvas de peces, Juveniles, Pesquería de gádidos, Zonas de desove, Zonas de cría, Relaciones tróficas, Disponibilidad de alimentos, Merlucciidae, Merluccius hubbsi, Merluza, ASFA15::S::Stocks, ASFA15::F::Fish larvae, ASFA15::J::Juveniles, ASFA15::G::Gadoid fisheries, ASFA15::S::Spawning grounds, ASFA15::N::Nursery grounds, ASFA15::T::Trophic relationships, ASFA15::F::Food availability, |
| Online Access: | http://hdl.handle.net/1834/6808 |
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