BACTERIOPLANKTON IN GAIRA BAY, CARIBBEAN SEA (COLOMBIA): COMPARISON OF ABUNDANCE AND BIOMASS VARIABILITY DURING DIFFERENT PERIODS

Abstract

Marine bacterioplankton abundance, biomass, biovolume and shape were quantied in three stations within Gaira Bay at the Colombian Caribbean coast over three periods dened for this study as: “rainy” (July, August, 2003), “transition” (April, October 2004) and “dry” (February, March, 2004). Bacterioplankton samples were collected from 0.5 and 42 m depths, ltered onto 0.22 μm polycarbonate lters and quantied using epi!uorescence microscopy with Acridine Orange staining and image analysis. Average bacterial abundance ranged between 1.3 x 105-2.9 x 106 cells mL-1 during the rainy period, 8.8 x 104-2.2 x 106 cells mL-1 during the transition period and 6.7 x 104-3.9 x 105 cell mL-1 at the dry period, with a mean abundance of 4.4 x 105 cells mL-1. The differences in abundance were statistically signicant between sampling periods, stations and depths, the differences in biovolume were statistically signicant between sampling periods and stations, nally, the differences in biomass were statistically signicant between stations and water depths (ANOVA, p<0.05). Most of the cells had a coccoid shape and a small biovolume (0.01-0.08 μm3 cell-1). Over the sampling period, the mean bacterial biomass ranged between 0.88 and 32.1 μg C L-1, with the maximum observed during the rainy period. The results suggest that bacterial biomass increases during the rainy period, probably as a consequence of increased water discharge originating from the Gaira River and the Ciénaga Grande de Santa Marta lagoon. We hypothesize that the temporal dynamics of bacterial communities in Gaira Bay are being driven by the availability of organic nutrients (DOC).