Planktonic microbial community oxygen consumption rate in Cananéia waters (25°S 48°W), Brazil

Water samples were taken monthly in 1976 at three sites along the Cananéia estuarine-lagoon system (25°S 48°W), on the southern coast of São Paulo State, Brazil. After screening through a 100 μm mesh silk screen, samples from two sites were size fractionated in classes between 100–50 μm, 50–10 μm and 10–0.45 μm and, concentrated. Oxygen consumption rates (OCR) of the fractionated and unfractionated surface samples were estimated after incubating in dark bottles at ‘in situ’ temperature. OCR varied from 0.26±0.95 to 41.61±2.56 μl O₂ l^?1 h^?1. Highest OCR was observed in summer, at the site under fresh-water influence. At this site, for most of the year, the smallest size category contributed mostly to total OCR. Bacteria attached to particulate matter appear to be responsible for most of the oxygen consumption measured. At the more saline waters, OCR was found to be associated with organisms in the 10–100 μm size class. At this site, size analysis of chlorophylla showed that the 0.45–10 μm size category comprised the major portion of total chlorophyll. The lack of association between the OCR dominant size class and the prevailing phytoplankton and bacteria size categories, suggests the oxygen consumption to be due to other organisms, probably nano- and microzooplankton. OCR measured in the unfractionated samples, at site 2, showed the same order of magnitude to those of the fractionated ones. At this site the importance of the bacterial metabolism in relation to the total OCR measured is discussed. It is concluded that in the surface waters of the Cananéia estuarine lagoon system the contribution of bacterial metabolism to total oxygen consumption differs along the system, being significant at the upper reaches of the estuary, where the inputs of organic matter are larger. In saline waters, in spite of high bacterial densities, oxygen consumption seems to reflect the metabolism of larger organisms.