| Summary: | Tese de doutoramento em Biociências, no ramo de Ecologia, apresentada ao Departamento de Ciências da Vida da Faculdade de Ciências e Tecnologia da Universidade de Coimbra Gelatinous carnivores’ zooplankton, commonly known as “jellyfish”, are ubiquitous organisms in neritic systems worldwide, with an important ecological role in the pelagic food chains. During the past several decades, their ever-increasing, mostly due to environmental perturbations and climate alterations, becoming a big concern for marine ecologists, due to the implications off their blooms on the zooplankton communities. In the Mondego estuary, the gelatinous zooplankton community is composed by higher Hydromedusae diversity and, also, by two colonial species, belonging to the order of Siphonophorae, the Calicophorans Muggiaea atlantica and its congener Muggiaea kochii, the former has constituted the most abundant gelatinous organisms in the Mondego estuary since 1994. The first chapter aimed to describe how changes in the species richness, the phenology, and the abundance of the gelatinous carnivores of the Mondego estuary during the period 2003-2013, were influenced by the North Atlantic Oscillations and its effect on regional atmospheric variability, such as on upwelling activity. During the 11-year time series, the most abundant gelatinous species were M. atlantica, Lizzia blondina, Obelia sp., Liriope tetraphylla, Solmaris corona and Clytia hemisphaerica. During the period investigated, the gelatinous community displayed phenological shifts, changed their mean annual pattern from unimodal to bimodal peak, before and after 2007, respectively. Also, the species richness increased since 2007-2008, with the increase presence of rare species. Shifts on the gelatinous community were connected to the atmospheric forces promoted by the NAO and its influence on upwelling activity and regional climate, as statistical analysis confirmed. The second chapter describes, more specifically, the spatial distribution on seasonal scale, of the two ...
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