Abundance and production of particle-associated bacteria and their role in a mangrove-dominated estuary

Abstract

A 1 yr study was carried out in the mangrove-dominated, tropical Mandovi estuary (Goa, India) to assess the contribution of particle-associated bacteria (PAB) to the system's variability in terms of abundance and productivity. The suspended load, which was composed of inorganic mineral grains and allochthonous materials including mangrove litter, was high during the southwest (SW) monsoon season. The ratio of organic:inorganic content of these particles was low during the pre- and post-monsoon seasons. PAB abundance ranged from 0.01 ×1010 to 22.8 ×1010 m-2 and accounted for 4to 94% of the total bacterial abundance. The variation in PAB abundance was due to their preferential colonization, which depended on the quantity and quality of the particles. The average annual PAB production was 214 μg C m-2 d-1 and contributed to an average of 35% of the total bacterial production. Primary productivity (PP) was 137, 14, and 163 μg C m-2 d-1 for the pre-monsoon, SW monsoon, and post-monsoon periods, respectively. The calculated maximum bacterial carbon demand (BCD) of PAB was 37% of the total BCD. On an annual basis, <1% of PP contributed to PAB-BCD. It is suggested that the rest of the BCD was met from mangrove litter and other allochthonous sources. Principal component analysis showed that biotic parameters were predictors for ̃50% of the variability and had a marked seasonality linked to salinity. The allochthonous sources contributed significantly to the structure of the biological community of this mangrove-dominated estuary.