Measurement of acid polysaccharides (APS) associated with microphytobenthos in salt marsh sediments

Abstract

Microphytobenthos (MPB) are an important component of shallow-water habitats where there is sufficient light to support benthic photosynthesis. Production of extracellular polymeric substances (EPS) is characteristic of the MPB, and acid polysaccharides (APS) are a major component of these EPS. A simple technique was developed to extract and measure APS concentrations in sediments. Water-extractable APS (wAPS) were extracted with ultra high purity water from lyophilized sediments. After centrifuging to remove the sediment, wAPS in the supernatant was precipitated with alcian blue, a cationic dye. The APS-alcian blue precipitate was removed by filtration. The remaining alcian blue in solution was determined spectrophotometrically and was inversely proportional to the concentration of wAPS in the sediment. Chlorophyll (chl) a, carbohydrate fractions, and wAPS were measured in sediments from 5 contrasting sites in a microtidal salt marsh in the subtropics. wAPS concentrations, expressed as gum xanthan equivalents, ranged from 152 to 6268 mg m-2 in the upper 5 mm of sediment. The biomass (determined as chl a) of MPB at all sites was highest in the winter compared to the summer. There was a significant correlation (r = 0.675, p < 0.001, n = 107) between sediment wAPS and chl a concentrations. The ratio of wAPS to saline-extractable EPS (sEPS) was significantly higher in summer compared to winter, indicating a seasonal change in the composition of EPS. These data show that APS are a significant and variable component of the EPS pool in salt marsh sediments. © Inter-Research 2009.