Influence of water circulation on marine and faecal bacteria in a mussel-growing area

Surface water and mussel samples were taken over a 2-year period in the southern part of Todos Santos Bay to follow the evolution of three different bacterial populations. The patterns and variability of viable heterotrophic bacteria, Vibrio-like organisms and faecal coliform populations were recorded to detect and assess the effects of pollution sources in this region, where mussel culture has recently been established. Faecal coliforms (FC) in surface waters had consistently low levels throughout the sampling period, normally under 14 FC 100 ml−1, the limit allowed by Mexican and US health agencies for areas dedicated to bivalve culture. We suspect that the southern part of Todos Santos Bay is protected from pollution generated in the north by its internal water circulation pattern, which is controlled in turn by the dominant winds in this region. A further implication of this circulation pattern is that the southern part of the area could be rapidly affected if organic wastes are discharged near the region of Punta Banda.