Primary production dynamics in seagrass beds of Mississippi Sound: the contributions of seagrass, epiphytic algae, sand microflora, and phytoplankton

Abstract

Primary production rates of four autotrophic components in Halodule wrightii beds off Horn Island were measured over an annual cycle. Hourly production rates varied from 0.9 mg C m-2 for H. wrightii leaves in winter to 1143 mg C m-2 for epiphytic algae during summer. Only 15% of the variation in hourly epiphytic algal production could be related to a single environmental variable (light energy). Variations in hourly production rates for the other productivity components were best explained by light energy, water temperature, tidal range and blade density; R2 for these regressions was 0.66 and 0.80 for phytoplankton and seagrass blades respectively. The epiphytic algal assemblage on H. wrightii leaves was dominated by the red alga Acrochaetium flexuosum and 12 taxa of araphid, monoraphid and biraphid diatoms. Phytoplankton over the beds were virtually all centric diatoms, whereas the microflora associated with the sandy sediments in which H. wrightii was rooted was dominated by small pennate diatoms. Annual production rates (g C m-2) were: epiphytic algae (905), phytoplankton (468), sand microflora (339) and H. wrightii (256). System production was dominated by the microalgae, with the contribution of H. wrightii blades being only 13% of the total. Epiphytic algae were the single most important productivity component, being responsible for 46 and 60% of total system and benthic production respectively. -from Authors