Bacterial growth rates and productivity within a seagrass system: seasonal variations in a Posidonia oceanica bed

Abstract

At 20 m depth in the Bay of Calvi, Corsica, over summer 1989 and winter 1990 there were only small variations in numbers of bacteria, decreasing by a factor of two from summer to winter. Significant variations in cell number were observed in summer 1990 where values ranged from 3.6-19.4 × 105 cells ml-1. Differences in bacterial biomass were more pronounced over the seasons and primarily determined by changes in abundance and biovolume of rod-shaped bacteria with a minimum of 6.8μg C l-1 in winter and a maximum of 81 μg C l-1 for summer 1990. Bacterial growth rates were at their maximum in summer (0.058 and 0.074 h-1 for 1989 and 1990 respectively). Doubling times varied between 12.8-36.2 h from July-September but 108.3-409.3 h from January-April. The estimated bacterial carbon production rates, amounting to 0.02-1.72 μg C l-1 h-1 in winter and 0.50-6.67μg C l-1 h-1 in summer, were not significantly different to rates obtained from the water column above the meadow during the same sampling period. The carbon requirements of the bacteria within the meadow are discussed and related to the available data on primary production and carbon release. -from Authors