Organic carbon decomposition, primary and bacterial productivity, and sulphate reduction, in tropical seagrass beds of the Gulf of Carpentaria, Australia

Abstract

Seagrass (mainly Enhalus acoroides, Syringodium isoetifolium, Cymodocea serrulata, Thalassia hemprichii and Cymodocea rotundata) gross productivity, determined by a lacunal gas technique, ranged from 0.5-4.3 g C m-2-1. In comparison, gross community productivity ranged from 4-9 g C m-2d-1. Macroalgae, epibenthic and epiphytic algae made the major contribution to gross primary production in the communities studied, contributing 40-90% of gross primary production. Most of the primary production was utilized by hydrolytic and fermentative bacteria and was ultimately oxidized by sulphate-reducing bacteria. Hydrolytic (aerobic) and fermentative bacterial productivity ranged from 3-13 g C m-2d-1 (integrated over a depth of 12 cm in the sediment). Highest rates of sulphate reduction coincided with the below-ground distribution of seagreass roots and rhizomes. Between 1.7-2.2 g C m-2d-1 was oxidized to CO2 by the sulphate-reducing bacteria, is equivalent to 30-80% of the net community productivity. -from Authors