O nanoflagelado heterotrófico de dimensões entre 4,8 e 7,0 µm (Pseudobodo tremulans) e uma bactéria heterotrófica, isolados das águas costeiras de Ubatuba, SP, Brasil, foram utilizados em experimentos com o objetivo de analisar quantitativamente as relações entre bactérias e nanoflagelados. O significado dos resultados obtidos em relação ao papel dos nanoflagelados heterotróficos no ecossistema costeiro de Ubatuba é discutido.

Heterotrophic nanoflagellate Pseudobodo tremulans (4.8 to 7.0 µm) and heterotrophic bacteria, isolated from coastal waters in Ubatuba, SP, Brazil, were used in experiments to analyze quantitatively the relationships between bacteria and nanoflagellates. The meaning of these results for the role of heterotrophic nanoflagellates in the Ubatuba coastal ecosystem is discussed.

A variação temporal da comunidade microbiana (bactérias, picofitoplâncton total e nanoheterótrofos) nas águas de Ubatuba (23°S 45°W) foi estudada durante um período de 7 dias (de 27/02 a 04/03/1988). As amostras foram obtidas na termoclina, duas vezes ao dia (na estôfa da maré baixa e da maré alta durante o período diurno. A densidade de nanoheterótrofos variou de 0,9 a 3,5 x 10³ cels m-1 apresentando valor médio de 2,3 x 10³ cels m-1. Picofitoplâncton total foi representado principalmente por cianobactérias cocóides e sua denside de variocões de 1,0 a 7,6 x 10(6) cels m-1. O número de bactérias variou de 1,0 a 2,7 x 10 cels m-l . A população bacteriana apresentou um padrão de oscilação defasado em relação a variação das concentrações de CI a. O intervalo de tempo entre os valores máximos de Cl a e as densidades máximas de bactéria foi de aproximadamente 24 horas. No início do período de estudo, a interrelação entre nanoheterótrofos e bactérias-picofitoplâncton foi caracterizada por uma oscilação inversa, sugerindo uma interação predador- presa. A partir do dia 02 de março as 3 populações variaram quase que em fase. As influências das condições meteorológicas, do movimento das marés e da predação por microzooplâncton e metazoários são discutidas. A despeito dos vários fatores que podem afetar as interrelações entre nanoheterótrofos e bactérias- picofitoplâncton parece que o padrão observado não é errático e pode estar expressando uma intensa atividade predatória.

An investigation on the temporal variation of the planktonic microbial community (bacteria, total picophytoplankton and nanoheterotrophs) was undertaken over 7 days period (from February 27 to March 4, 1988) in a coastal region of Ubatuba (23°8, 45°W). Samples were obtained at the thermocline twice daily (at high and low tides) during daylight time. Average density of nanoheterotrophs (Nh) was 2.3 x 10³ cells m-l, ranging from 0.9 to 3.5 x 10 cells mrl. Total picophytoplankton was represfnted mostly by chroococcoid cyanobacteria and varie2 from 1.0 tp 7.6 x 10(4) cells m-l. Bacterial numbers ranged from 1.0 to 2.7 x 10(6) cells m-l. The oscillation pattern displayed by the bacterial populations was out of phase in relation to Chl-a variation. The time interval between Chl-a peak and the bacterial one was approximately 24 hours. At the beginning of studied period, the interrelationship between nanoheterotrophs and bacteria-picophytoplankton was characterized bya coupled oscillation, suggesting a predator- prey Interaction. During the last three days (Marsh 2-4) the densities of three populations have fluctuated in phase. The influences of weather conditions, tIdal movements, and predation by microzooplankton and metazoans are discussed. Many factors can affect the relationships between nanoheterotrophs and bacterial-picophytoplankton, but the oscillation pattern observed in this report are not fortuitous and may indicate an intense predation activity of nanoheterotrophs on pico-organisms.

No presente estudo foram analisados em laboratório, sob temperaturas de inverno e verão, aspectos quantitativos da alimentação de Hyale media (Crustacea-Amphipoda), utilizando-se o método gravimetría), aliado ao conteúdo de carbono dos itens alimentares oferecidos. Nos experimentos com temperatura de inverno não foi encontrado diferença significativa nas taxas de assimilação entre os diferentes estádios de desenvolvimento e sexo. Naqueles com temperatura de verão as taxas de assimilação para fêmeas ovígera e não ovígera foram maiores que aquelas encontradas para machos adulto e jovem. As variações encontradas nas taxa e eficiência de assimilação foram explicadas pelo efeito diferencial da temperatura sobre a taxa de crescimento específico e condições fisiológicas de cada estádio de desenvolvimento.

The feeding of Hyale media was analysed under laboratory conditions in winter and summer temperatures. The results showed that assimilation rates increased following food ingestion rates and decreased when egestion rates increased. In winter temperatures no significant differences were found in the assimilation rates among developmental stages and sexes. In summer temperatures assimilation rates for ovigerous and non-ovigerous females were higher than those found for adult and young males. Although not statistically analysed, mean assimilation efficiencies were highest among ovigerous females and adult males, in summer. The quantitative and qualitative variations found in the assimilation efficiency and rates were explained by the differential effect of temperature on the specific growth rate and in the physiological conditions of each growth stage concerned.

Oxidable POC, at two stations in the Cananéia estuary, was found to be largely dependent upon the smallest size POC. The correlation factors between POC and the numerical abundance of cells, heterotrofic particles and bacteria, in each of the size categories studied, were generally low and non-significant for both stations, with a few exceptions. At St. I the number of heterotrophic particles seems to account for some of the POC variation over the year. At St. II, the only significant correlation found was between the number of the largest and intermediate size classes bacteria and the equivalent size classes POC. At this station the importance of the detritus component is suggested. The differences found between the stations, concerning the numerical contribution of cells, particles and bacteria to total POC, have been attributed to the differential hydrodynamic conditions acting upon material coming from land, due to diverse location of the stations. Sampling date and the collection of different water masses have also been considered as factors that may greatly affect the relationships studied.