Diel variation of bacterial abundance and productivity in tropical coastal lagoons: the importance of bottom-up

factors in a short-time scale.

FARJALLA^1,2, V.F.; LAQUE¹, T.; SUHETT¹, A.L.; AMADO¹, A.M. & ESTEVES¹, F. DE A.

¹ Laboratório de Limnologia, Departamento de Ecologia, Instituto de Biologia, CCS, Bloco A, UFRJ, Ilha do Fundão, Rio de Janeiro, RJ, Brasil. CEP:21941-590. C. Postal: 68020

farjalla@biologia.ufrj.br

² Núcleo de Pesquisas Ecológicas de Macaé (NUPEM/UFRJ). Parque de Exposições Latiff Mussi Rocha, Rod. Amaral Peixoto km. 181, C. Postal: 119331 São José do Barreto, Macaé, Rio de Janeiro.

 ABSTRACT: We analyzed the diel variation of some limnological variables and its effects on the abundance and secondary productivity of bacterioplankton in two tropical coastal lagoons located in Southeastern Brazil (Rio de Janeiro State). Bacterial abundance and secondary productivity remained constant throughout the day in Cabiúnas lagoon, as the water temperature and the dissolved oxygen concentration. On the other hand, Garças lagoon showed a wide diel variation in water temperature, reaching values close to 39 ºC at 16:00 h. The oxygen concentration varied throughout the day, surpassing 10 mg O2.L-1 at noon and dropping to less than 3 mg O2.L-1 during the night in Garças lagoon. Despite the fact that bacterial abundance remained constant in Garças lagoon, bacterial productivity varied throughout the day. Bacterial productivity was higher at night, in the period of oxygen depletion and lower temperatures. The high temperatures observed in Garças lagoon during the day seem to be detrimental to bacterial metabolism, probably due to denaturation of bacterial enzymes. Thus, in shallow tropical ecosystems, as is particularly the case for most of coastal lagoons, the daily temperature variation may be an important factor regulating bacterial production in a short-time scale, with great implications for the metabolism of these ecosystems.

Key-words: planktonic bacteria, bacterial production, diel variation, bottom-up factors, coastal lagoons.