PARENT SESSION
Poster Session #12: Marine Ecology.
Monday, August 5. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC
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Bioturbation by Nereis diversicolor and stability of estuarine sediments.
Fernandes, Sandra1, Sobral, Paula*,1, 1 IMAR - Universidade Nova de Lisboa, Lisboa., Portugal
ABSTRACT- Biological processes are a major component of the sedimentary cycles in low energy areas such as intertidal mudflats. Bioturbation by intertidal endofauna is known to modify sediment properties and thus influence its resistance to erosion. In this work the effect of bioturbartion by the polychaete Nereis diversicolor, a gallery builder, on the stability and erosion of estuarine sediments was tested using a annular flume. Cohesive intertidal sediments were collected from Ponta da Erva (Tejo estuary, Portugal) in March and October and stabilized in the laboratory in flume boxes with different densities of N. diversicolor (260, 370, 450 indm-2). Organic content of the sediment was 8-9%. After a stabilization period of 20 days (photoperiod: 8 h at 57 
E.m-2s-1), boxes were introduced in the flume and exposed to increasing free-stream velocities from ~0 to 50 cms-1 resulting in shear velocities (u*) up to 3.7 cm s-1. Water samples were collected at selected velocities for suspended and organic particulate matter and Chla determinations. Resuspension varied greatly between March and October (~2-4 gL-1 for the highest velocity) and bioturbation by N. diversicolor at densities >= 370 indm-2 resulted in a further increase in suspended particles and consequently erosion. At the highest density N. diversicolor reduced Chla probably by ingestion and transport to deeper layers as a result of sediment mixing. Our results highlight the role of N. diversicolor as a destabilizer of surface sediments. The need to integrate biological processes in hydrodynamic sediment transport models to improve coastal and estuarine management is also stressed.
KEY WORDS: Nereis diversicolor, bioturbation, sediment stability and erosion