Particle-associated bacterial dynamics in a tropical tidal plain (Zuari estuary, India)

The dynamics of particle-associated bacteria (PAB) in a tropical estuary, Zuari, in Goa on the west coast of India, was studied for a year from September 1997 to October 1998. Bacterial abundance, productivity and enzymatic activities were measured at a fixed station in the estuary. The study period covered pre-monsoon (February to May), southwest monsoon (June to September) and post-monsoon (October to January) seasons. Particulate organic carbon ranged from 0.5 to 17.5 mg C l(-1). Particles of size range >3 to <220 pin were the most abundant, were rich in organic carbon (similar to60%), and formed 55% of the suspended load (ave. similar to0.1 g l(-1)) in the estuary. PAB ranged from 8.8 x 10(7) to 3.9 x 10(10)1(-1) and the waters close to the sediment had a higher abundance than the surface waters. PAB varied seasonally and accounted for 20 to 80% of the total bacterial population. The mean rate of production as measured by H-3-thymidine incorporation was 70 mug Cl-1 d(-1) in the surface and 35 mug C l(-1) d(-1) in the bottom waters. Monthly production varied by 2 orders and was not coupled to abundance. However, high production during the monsoon was fuelled by allochthonous input of organic matter. No linear relationship was observed between biological parameters and other measured environmental parameters except for temperature, which showed a linear relationship with PAB and particle numbers. The bacterial carbon demand (BCD) at the station was higher than the primary production (PP) and was met by allochthonous input. Our Study demonstrates that the PAB dynamics were determined by the availability of substrates and resuspension of sedimented materials.