O ciclo de vida dos dinoflagelados oceânicos tem sido pouco estudado. A divisão é iniciada em determinados tempos do dia (divisão celular faseada). Este estudo relata os estágios de divisão (zona e ponte dorsal megacítica) para a população de Ornithocercus, no Oceano Atlântico Sul (Arquipélago de Fernando de Noronha), em diferentes tempos do dia. As amostras foram coletadas a cada 3h, durante 24h, em dois pontos fixos, nos anos 2010 e 2012. Foi feito o arrasto vertical da rede de plâncton (malha de 20µm). As células em divisão de Ornithocercus foram registradas, em que ocorreram O. magnificus Stein, O. thumii (Schmidt) Kofoid & Skogsberg, O. quadratus Schütt e O steinii Schütt, os quais apresentaram a divisão faseada e pelo menos um dos estágios de divisão celular. O. quadratus ocorreu no maior número de horários, desde antes, durante e depois do amanhecer, bem como durante e depois do pôr do sol. Palavras chave: fitoplâncton, dinoflagelados, variação nictemeral.
Abstract:We aimed verify the composition of the phytoplankton community and this life forms that occur in the Capibaribe River estuary, Pernambuco, Brazil. This is a highly impacted ecosystem by anthropic activities. We collected samples of the phytoplankton community at three stations, during three months of each season: dry, from October to December 2010; rainy, from May to July 2011. We collected samples during the low and high tide, at the spring tide. We classified the species based on life forms. We identified 127 taxa, and the majority of species were freshwater planktonic form (FP; 30%), followed by marine oceanic planktonic (MOP; 25%), marine neritic tichoplanktonic (MNT; 22%) and planktonic (MNP; 19%,), and tichoplanktonic estuarine (TE; 3%) and freshwater (TF; 1%). The majority of species identified were diatoms, since it assumes the most variability of life forms, therefore enabling its presence in the different portions at the estuary.
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