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Título

Microzooplankton feeding impact in three different European coastal systems

AutorTeixeira, I. G.
DirectorFigueiras, F. G. ; Lobo da Cunha, Alexandre
Palabras claveMicrozooplankton
Coastal systems
Coastal ecology
Fecha de publicación2009
ResumenIn this work, the microzooplankton feeding impact on the plankton community has been assessed in three systems along the European coast: an embayment in Spain (Ría de Vigo), a shallow fjord in Denmark (Limfjord) and a shallow basin in the Netherlands(Oosterschelde). This was achieved by performing the dilution method (Landry & Hassett 982) associated with microscopic enumeration and identification, which allowed determining the production of the several components of the plankton community, both autotrophic and heterotrophic, and their consumption by microzooplankton. The dilution method, albeit being the most widely used experimental technique to estimate the microzooplankton feeding impact in marine systems, can present several problems regarding the correct accomplishment of the basic assumptions on which it relies. In the first part of this work (section 2), the violation of these basic assumptions was analysed in relation to the observed deviations from linearity in a relationship that theoretically should be linear. Non-linear responses, which are also frequently reported in the literature but rarely analysed, were related to the non-linear feeding behaviour of the microzooplankton, which at high food availability reaches the maximum ingestion rate and enhances their selectivity for certain preys. These findings, which do not invalidate the use of this technique, provide further evidence for the introduction of some changes in the protocol in order to optimize its use. In the following three sections (3, 4 and 5), the estimation of the microzooplankton feeding impact in the three coastal systems referred above, provided an insight into the impact of microzooplankton on different communities and under contrasting environmental conditions. In the seasonal study performed in the coastal upwelling system of the Ría de Vigo (section 3), the microzooplankton feeding impact on the several plankton groups varied over the year. Predation on heterotrophs was very constant and relatively more important during downwelling conditions, when consumption of phytoplankton was low. During upwelling, the main food source for microzooplankton was phytoplankton, mainly diatoms. In the Limfjord (section 4), the hydrodynamics of the system, characterized by stratification-mixing cycles during 9 successive sampling days, was very important for the coupling between the benthic and pelagic systems. Mixing events enhanced this coupling, favouring a short food chain where the impact of microzooplankton was lower. In contrast, stratification periods favoured the microbial food web and the decoupling between benthic and pelagic communities. In the Oosterschelde (section 5), microzooplankton was observed to have an important role during a bloom of the colonial haptophyte Phaeocystis sp., either from direct consumption of this algae, or from consumption of heterotrophs which were favoured by the dissolved organic matter released during the collapse of the bloom. Major findings from this work are related to the validity of the use of the dilution technique, even when non-linear responses are obtained, and to the determination of the important role that microzooplankton plays in coastal systems as consumers of the several autotrophic and heterotrophic plankton groups. The understanding of the importance of microzooplankton in marine systems aids to a better knowledge of their functioning, enabling to develop more accurate models and predictions under the several environmental conditions.
URIhttp://hdl.handle.net/10261/14344
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