Objective: Benthic diatoms secrete extracellular polymeric substances (EPS) that may contribute to the stability and erosion threshold of intertidal sediments. The objective of this project is to study the effects of global change on coastal sediment erosion. These include effects of nutrient availability, CO22 concentration, temperature, salinity, light and other factors. These factors control growth, photosynthesis and EPS secretion by benthic diatoms and hence effect sediment erosion. This project aims to investigate how these factors control the quantity and quality of EPS secreted by a number of diatoms. Approach: A number of different benthic diatoms have been isolated from various intertidal mudflats and grown in culture in the laboratory. The production of EPS by cultures of these diatoms will be investigated. A method will be developed to extract EPS from these diatoms. Different carbohydrate and EPS fractions can be distinghuished. One is the mucilage, which is excreted into the medium, is not or only loosely associated with the cells. It can be obtained by centrifuging the culture. Another fraction is more tightly associated with the cells and can be extracted using warm water. These fractions will be analyzed quanitatively and qualitatively. This includes the identification of molecular weight, monoscaccharide composition, presence of uronic acids and sulfated sugars. In addition to EPS the dynamics of intracellular polysaccharides and simple carbohydrates will also be investigated. The effect of various factors on the production of carbohydrate will be investigated. These include nutrient and CO2 availability, light, temperature, salinity and other factors. EPS secreation in diatoms is closely associated with photosynthesis, and therefore the effect of various environmental factors on this proces will also be taken into account. It will be assessed how much of the photosynthetic capacity is diverted to EPS. In addition, it will be investigated whether diatoms are capable of hydrolyssis of EPS. It is hypothesized that benthic diatoms may posses exo-orectoenzymes that are capable of hydrolysis of EPS. The significance of these controlling factors for natural mudflat communities will be checked by some experiments in the field. One of the main filed sites is located in the Gironde estuary in France. The local field site will be the Biezelingse Ham (Westerschelde).
