) indicated the establishment of a herbivorous food web structure. Particulate organic carbon (POC) production was mainly due to phytoplankton (98%) and did not differ between periods. However, the observed variability in plankton trophic interactions should affect the magnitude of POC export from this dynamic system. KEY WORDS: Food webs · Carbon fluxes · Bacterioplankton · Phytoplankton · Zooplankton · Cabo Frio · South Brazil Bight Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 363: [109][110][111][112][113][114][115][116][117][118][119] 2008 small phytoplankton and bacteria to larger zooplankton and then higher pelagic trophic levels is mediated by heterotrophic nano-and micro-sized protists (Sherr et al. 1986). Therefore, in these microbial food webs, most of the biogenic carbon produced is recycled within the system through heterotrophic respiration (Legendre & Le Fevre 1995).In contrast, in more eutrophic systems with low vertical stability, larger phytoplankton cells are more representative and usually dominant, where turbulence simultaneously provides nutrient and prevents sinking below the euphotic zone (Kiørboe 1993). In those conditions an herbivorous food web prevails and most of the POC produced is exported via grazing, as the mesozooplankton are the dominant primary consumers (Legendre & Rassoulzadegan 1996). Moreover, carbon export is directly related to the input and uptake of 'new' nutrients, mainly nitrate (N-NO 3 ) to the euphotic zone (Dugdale & Goering 1967), and this nitrogen form is primarily utilized by larger cells, such as diatoms (Price et al. 1985).Coastal waters influenced by upwelling are among the most productive aquatic systems. The periodical wind-driven transport of surface waters offshore and the consequent upwelling of deeper water masses provide enrichment to previously oligotrophic waters. The high nutrient input to the surface waters, especially N-NO 3 , stimulates phytoplankton production, mainly for larger species, resulting in higher mesozooplankton and fisheries productivity. This pattern has been described for several upwelling zones around the world, such as those in the SE Pacific Ocean , Iriarte & Gonzalez 2004, Fernandez-Alamo & Farber-Lorda 2006, NE Pacific Ocean (Peterson et al. 1979, Collins et al. 2003, NE Atlantic Ocean (Bode et al. 2003), and Indian Ocean (Brown et al. 2002).Upwelling zones usually occur along eastern ocean boundaries, between 30°N and 30°S, due to the dominance of the trade winds. In the SW Atlantic, however, the change in the coastal direction at 23°S (Cabo Frio, SE Brazil) from N-S to E-W, along with the proximity of the 100 m isobath to the coast, allow the NE winds to move surface waters offshore and the consequent upwelling of the South Atlantic Central Water (SACW). This results in a high productivity core in the midst of the otherwise oligotrophic Brazilian Current waters (Valentin 1984a). The upwelling of deeper water masses is reversed when shifts in wind direction bring surface w...

A B S T R A C TThe dynamics of the plankton compartments at the entrance of Guanabara Bay (SE Brazil) were assessed during a short-term temporal survey to estimate their trophic correlations. Size-fractioned phytoplankton (picoplankton: < 2µm, nanoplankton: 2-20µm and microplankton: > 20µm) biomass and photosynthetic efficiency, composition and abundance of the auto-and heterotrophic nano-and microplankton, and mesozooplankton were evaluated at a fixed station for 3 consecutive days at 3-h intervals, in the surface and bottom (20m) layers. The variability of almost all plankton compartments in the surface layer was directly dependent on temperature, indicating the great influence of the circulation at the entrance of the bay on plankton structure. In the surface layer, the mesozooplankton seems to be sustained by both autotrophic nano-and picoplankton, this last being channeled through the microzooplankton. Near the bottom, both auto-and heterotrophic microplankton are probably supporting the mesozooplankton biomass. Our findings thus suggest that the entrance of Guanabara bay presents a multivorous food web, i.e., a combination of both grazing and microbial trophic pathways. R E S U M OA dinâmica dos vários compartimentos do plâncton foi avaliada durante uma série de curta duração na entrada da baía de Guanabara (SE do Brasil), com o objetivo de estimar suas correlações tróficas. A biomassa e eficiência fotossíntética das três frações do fitoplâncton (picoplâncton: < 2µm, nanoplâncton: 2-20µm e microplâncton: > 20µm), juntamente com a composição e abundância do nano-e microplâncton auto-e heterótrofos e do mesozooplâncton, foram determinadas em uma estação fixa durante 3 dias consecutivos, a intervalos de 3h, nas camadas de superfície e de fundo (20m). A variabilidade de quase todos os compartimentos do plâncton na superfície foi diretamente relacionada à temperatura, indicando forte influência da circulação da entrada da baía na estrutura planctônica. Na camada superficial, o mesozooplâncton parece ser alimentado pelo nano-e picoplâncton autótrofos, esse último sendo sustentado pelo microzooplâncton. Próximo ao fundo, o microplâncton auto-e heterótrofo estão possivelmente sustentando a biomassa mesozooplanctônica. Nossos resultados sugerem, portanto, que na entrada da baía de Guanabara esteja estabelecida uma rede trófica multívora, i.e., uma combinação entre as cadeias microbiana e de pastagem.

The aim of this study was to determine the development time of embryos and to estimate the hatching rates of resting eggs of cladocerans found in the sediment of Guanabara Bay, Rio de Janeiro, Brazil, under experimental conditions. Eggs were sorted by species (Penilia avirostris -Sididae; Pleopis polyphemoides and Pseudevadne tergestina -Podonidae) and incubated at a temperature of 25 °C, salinity 35 and photoperiod 12 hours light/ 12 hours dark. Hatching rates were about 38% for Pseudevadne tergestina and 28% for Pleopis polyphemoides. Embryos of resting eggs of Penilia avirostris developed comparatively slowly (hatching after 86 days of incubation), with a hatching rate of only 5%. It was observed that development and hatching of resting eggs of marine cladocerans suggest that pulses of recruitment may exist, thus contributing to the rapid appearance and maintenance of planktonic populations of these crustaceans in Guanabara Bay.Keywords: Cladocera, resting eggs, hatching, Guanabara Bay, Brazil. Taxas de eclosão de ovos de resistência de 'Cladocera' (Crustacea; Branchiopoda) em uma baía tropical, BrasilResumo O objetivo do presente estudo foi determinar o tempo de desenvolvimento de embriões e estimar as taxas de eclosão de ovos de resistência de cladóceros encontrados no sedimento da baía de Guanabara, Rio de Janeiro, Brasil, sob condições experimentais. Os ovos foram separados por espécie (Penilia avirostris -Sididae; Pleopis polyphemoides e Pseudevadne tergestina -Podonidae) e incubados a 25 °C, salinidade 35 e fotoperíodo 12 horas claro/ 12 horas escuro. As taxas de eclosão foram de aproximadamente 38% para Pseudevadne tergestina e de 28% para Pleopis polyphemoides. Os embriões dos ovos de resistência de Penilia avirostris desenvolveram-se de forma relativamente lenta (eclodindo apenas 86 dias após o início da incubação), com uma taxa de eclosão de apenas 5%. Foi observado que o desenvolvimento e a eclosão dos ovos de resistência de cladóceros marinhos sugerem que podem ocorrer em pulsos, contribuindo assim para o rápido aparecimento e manutenção destes crustáceos na baía de Guanabara.Palavras-chave: Cladocera, ovos de resistência, eclosão, baía de Guanabara, Brasil.