* Correspondence address: Universite H de La Rochelle, De H pt. de Biologie, Avenue Marillac, 17042 La Rochelle, France. Tel.: #33-5-46-45-85-52; fax: #33-5-46-45-82-64. E-mail address: gerard.blanchard@univ-lr.fr (G.F. Blanchard). Continental Shelf Research 20 (2000) 1243}1256 The e!ect of geomorphological structures on potential biostabilisation by microphytobenthos on intertidal mud#ats G.F. Blanchard*, D.M. Paterson, L.J. Stal, P. Richard, R. Galois, V. Huet, J. Kelly, C. Honeywill, J. de Brouwer, K. Dyer, M. Christie, M. Seguignes Universite & de La Rochelle, De & pt de Biologie, Avenue Michel Cre H peav, 17042 La Rochelle, France CNRS-IFREMER, CREMA L+Houmeau, BP5, 17137 L+Houmeau, France Gatty Marine Laboratory, University of St. Andrews, St. Andrews, Scotland KY16 8LB, UK NIOO-CEMO, P.O. Box 140, NL-4400 AC, Yerseke, Netherlands IMS, University of Plymouth, Drake Circus, Plymouth, Devon, PL4 8AA, UK Received 17 May 1999; received in revised form 14 November 1999; accepted 18 November 1999 Abstract The chlorophyll a and colloidal carbohydrate content of sediments were measured at Ske%ing mud#at in the Humber estuary, UK, in July 1997 as part of a "eldwork experiment carried out within the framework of the INTRMUD project. The aim was to analyse the spatial variations of Chl a and colloidal carbohydrate concentrations within the surface 1 cm of sediment (together with physical variables) in the di!erent macroscopic sedimentary struc- tures found at four stations along a cross-shore transect. The underlying assumption was that epipelic microalgae (Chl a) produce extra cellular polymeric substances (EPS), largely com- prised carbohydrates, when migrating vertically at the sediment surface. This organic material binds sediment particles and thus contributes to enhance sediment cohesiveness/stability. Therefore, the shape and the strength of the relationship between Chl a and colloidal carbohy- drates are fundamental for assessing the role of autotrophic microbial communities in bio- stabilisation processes. At station A, the highest level of the mud#at, there were no obvious sedimentary features, while a ridge (crest) and runnel (trough) system was present at mid-tidal stations (B and C). At station D, the sediment was sandier; crests and troughs were obvious but did not form a ridge and runnel system as at stations B and C. Taking all data together, a signi"cant positive linear relationship between colloidal carbohydrates and Chl a was found, but analysing data separately by station indicated that there was no relationship between 0278-4343/00/$ - see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S 0 2 7 8 - 4 3 4 3 ( 0 0 ) 0 0 0 2 1 - 2