Objective: Intertidal mudflats may sustain extended biofilms of benthic diatoms. It is assumed that these diatoms play an important role in the stability of these sediments. Diatoms may secrete extracellualr polymeric substances (EPS), which are composed primarily of polysaccharides that may act as glue and consolidate the sediment surface. The objective of this project is to investigate the conditions that control the secreation of EPS by diatom biofilms and its fate in mudflats and to assess the relation of EPS dynamics to sediment stabilization. Approach: Diatom biofilms from different European mudflats are investigated. The main sites studied are: the biezelingse Ham (Westerschelde) and the Heringsplaat (Ems-Dollard estuary) in the Netherlands, the Humber estuary and St. Andrews in the United Kingdom and the mudflat of Marennes-Oleron in France. The diatom biomass is determined by analysis of the specific pigments using HPLC. A method was developed to extract and analyze 2 different operational fractions of EPS. One fraction is extracted by water and another fraction is extracted by 100 mM EDTA. The water-extractable EPS fraction is loosely bound to the sediment and is probably mainly composed of neutral sugars. This colloidal carbohydrate is probably largely removed from the sediment each time it is inundated and could therfore represent an important carbon source for filter feedders. The EDTA-extractable carbohydrate contains uronic acids and sulfated carbohydrates. Thsi fraction is probably important for binding sediment particles through the interactions with charged groups. The 2 operational fractions of EPS will be characterized qualitatively and quantitatively. The fractions that control their production will be investigated. The realtion between diatom species, EPS secreation and sediment characteristics will be subject of study. In order to achieve this, different sampling sites in one intertidal mudflat will be compared, but also comparisons between different mudflats will be made. In addition, seasonal variations will be taken into account. Diatoms may secrete EPS as a result of unbalanced growth or as part of their migratory behavior. The interaction of EPS secreation and photosynthesis in diatom biofilm will be investigated. By using a Cohesive Strength Meter (CSM) the relation between EPS content and sediment stabilization will be measured. The fate of EPS will be studied by studying its degradability. Planning 2000: The chemical and physical characteristics of the two operational carbohydrate fractions will be studied in more detail using HPLC, ultafiltration (chemical characterization), rheology and IPV (physical characterization). Furhtemore, experiments with diatom cultures and field material will be conducted, to get a better understanding of short-term EPS dynamics.
Hummel H. 1998: Benthos on the Biezelingse Ham as part of INTRMUD. Netherlands Institute of Ecology; Centre for Estuarine and Marine Ecology, Netherlands. Metadata available at http://mda.nioo.knaw.nl/imis.php?module=dataset&dasid=1006, meer
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