Density-dependent effects of bioturbation by the clam, Scrobicularia plana, on the erodibility of estuarine sediments
Claudia Soares A B and Paula Sobral AA IMAR – Institute for Marine Research, FCTUNL, Campus da Caparica, 2829-516, Caparica, Portugal.
B Corresponding author. Email: csps@fct.unl.pt
Marine and Freshwater Research 60(7) 737-744 https://doi.org/10.1071/MF08069
Submitted: 1 March 2008 Accepted: 27 March 2009 Published: 28 July 2009
Abstract
Benthic organisms are known to modify sediment properties and influence the flux of materials to the water column. In this study, the density-dependent effects of bioturbation by the estuarine clam, Scrobicularia plana, on the biogeochemical properties and erodibility of the sediment were assessed using laboratory annular flumes. Sediments with different mud contents (~98% and 90%) were collected undisturbed from two different sites of the Tagus estuary. S. plana were added to the sediment at increasing densities (0, 57, 115 and 229 ind m–2) and left to bioturbate the sediment before the experimental erosion runs. All erosion runs were carried out following a stepwise increase of current velocities (U) up to 0.25 m s–1. Sediment chlorophyll a, pheopigments and extracellular polymeric substance fractions were measured at the time of sampling in the field and in the end of the erosion runs. Increasing densities of S. plana in the muddier sediment raised eroded mass, while the sediment with less mud behaved as non-cohesive and registered a decrease in eroded mass possibly due to a switch in the feeding behaviour of S. plana.
Additional keywords: annular flumes, erosion rates, muddy sediments, Tagus estuary.
Acknowledgements
The authors thank the Guest Editor and reviewers for their pertinent comments, which greatly contributed to improving the manuscript. We also thank Fernando Marques at the University of Lisbon for the grain-size analysis and Filipe Santos for his invaluable help during field work. This work was part of the Project ERODES (POCI/AMB/59262/2004) funded by the Portuguese Foundation for Science and Technology under the POCI 2010 Program and co-funded through FEDER.
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