Production and enzymatic hydrolysis of carbohydrates in intertidal sediment

A significant proportion of microphytobenthos (MPB) production is in the form of intra- and extracellular carbohydrates. We measured changes in MPB biomass, associated carbohydrates, and relative exoenzyme activity in an intertidal biofilm over the course of daylight tidal emersion. Two experiments were carried out in North Inlet (South Carolina, USA) during June 2007. MPB biomass accumulated in the upper 5 mm of sediment during daylight emersion, and there was a loss of biomass after tidal flooding of the sediment, with a 50 +/- 21% (mean +/- SD) decrease in sediment chl a content. Six carbohydrate fractions were measured in the sediment, and there were significant positive correlations between chl a and all carbohydrate fractions, indicating that the MPB was the major source of carbohydrates in the sediment, despite significant local primary production by Spartina alterniflora. Rates of relative glycosidase activity followed the pattern: b-glucosidase > alpha-glucosidase > (b-xylosidase = b-galactosidase = alpha-galactosidase). Glucosidase enzymes dominated the hydrolysis of carbohydrates, contributing 70 +/- 6% of the measured total relative exoenzyme activity. There were significant positive correlations between the total and hot water-extracted carbohydrates in the sediment with relative alpha-glucosidase activity. Relative alpha-galactosidase activity was positively correlated with the saline-extractable and saline-extractable low molecular weight fractions. In addition to b-glucosidase, other exoenzymes play a significant role in the remineralization of exopolymers in MPB-dominated intertidal sediments.