A variação temporal de densidade e dos parâmetros populacionais de Pseudevadne tergestina foi estudada na Baía de Guanabara. As coletas foram realizadas na superfície de uma estação fixa, a cada 3-4 dias, de fevereiro a agosto de 2000. Os máximos de abundância dessa espécie foram observados em março, com densidades variando de 20 a 600 ind.m-3. Foram calculadas as taxas de nascimento (0,25-0,90 ind.dia-¹), de crescimento (-0,30 -0,90 ind.dia-¹) e de mortalidade (-1,6 - 1,9 dia-1). O início da população pode ser atribuído ao aumento da temperatura e à eclosão dos ovos de resistências. A população entra em colapso no outono - inverno, como conseqüência dos efeitos combinados de diversos fatores: a diminuição da temperatura da água (de 27ºC para 21ºC) influenciando o tempo de desenvolvimento dos ovos (de 2,27 para 3,28 dias), a predação por Chaetognatha cuja densidade alcançou 100 ind.m-3 e a mudança de estratégia reprodutiva de P. tergestina, de partenogênica para gametogênica. O transporte das águas pelas correntes contribui também na redução da densidade populacional dessa espécie.

Populations of Pseudevadne tergestina were studied in Guanabara Bay, southeastern Brazil, to assess temporal variations in density and population dynamics. Data on temperature, salinity and zooplankton samples were taken from the superficial water of a fixed station, every 3 - 4 days, from February 2 through August 1, 2000. The highest abundance of this species was observed in March, when densities varied widely, from 20 to 600 ind. m-3. Population parameters were calculated, such as birth rate (from 0.25 to 0.90 ind.-1.day-1), growth rate (from -1.30 to 2.09 day-1 ) and death rate ( from -1.6 to 1.9 day-1 ) Start of population could be attributed to the increase of temperature and to the hatching of resting eggs. The population collapsed in fall-winter, as result from the combined effects of different factors: decrease of water temperature (from 27ºC to 21ºC) influencing egg development time (from 2.27 to 3.28 days); predation pressure by chaetognaths (Max. 100 ind. m-3 ) and switch of population from parthenogenic to sexual reproduction. Horizontal transport of water by tidal currents contributed partially to the reduction of population density.

A first recordof Pleopis schmackeri (Poppe,1889) (Branchiopoda, Onychopoda) in the Guanabara Bay, Rio de Janeiro, Brazilis described.This marine cladoceran species occurred in zooplanktonic samples obtained on June 26, 2000, with densities ? 4.0 ind.m-3. Its presence may berelated with inflow of coastal waters to the bay.

Two species of marine cladocerans, Penilia avirostris Dana, 1852 and Evadne tergestina Claus, 1877 were collected in thirteen samples at a fixed station in Guanabara Bay, Rio de Janeiro (30-meter depth) by means of vertical tows with a 200 µm mesh size net at different times from September 12th to 15th, 1995. The parthenogenetic females of Evadne tergestina bore mature embryos (with pigmented eye) only in the samples collected at night, whereas Penilia avirostris at any time of day. This phenomenon was interpreted based on the greater visibility of the Evadne tergestina brood: one of the benefits for embryo maturing during the darkness period would be a decrease of predation on gravid females.

This note relates the occurrence of Evadne spinifera Müller, 1867 (Crustacea, Branchiopoda) in Guanabara Bay, Rio de Janeiro State, Brazil. The samples were obtained by vertical tows with a 200µm mesh-size conical net at different times over a four day period in September, 1995. Evadne spinifera densities was always low.