Bacteria in the Maciel tidal creek (Paraná, Brazil): a subsidy for oyster cultivation

Abstract

Oysters are bivalve mollusks usually consumed raw, that are filter feeders on phytoplankton from the surrounding sea-water, during the entire life cycle. Due to the efficient filtration mechanism they are able to accumulate, from the adjacent seawater big amounts of microorganisms. Thus they may act as bearers of human pathogenic microorganisms. In Paraná they are cultivated in the mud, in tables (both in the intertidal area) and in “long line” (between the tide channel and the margin). In this research the quantitative variability of the number of total heterotrophic bacteria, bacterial biomass, total coliforms and Escherichia coli in the margins and in the tide channel of Maciel's tidal creek was studied. The relationships among the bacterial values and physical-chemical factors of the water: temperature, salinity, pH, dissolved oxygen, suspended particulate matter, particulate organic matter and chlorophyll a were analyzed. The results showed that there was not significant variability of chlorophyll a among the stations, suggesting that, in relation to the feeding mode of the oysters they could be cultivated at any place of the gamboa. E. coli values indicate that Maciel's tidal creek is not proper for the cultivation of oysters that are to be consumed raw without previous purification. However, values significantly higher of this microorganism registered in the margins indicate that the most suitable cultivation method is of the type "long line” that should be located between the margins and the tide channel.