Density dependence effect on bioturbation: a case study of Laeonereis culveri (nereidae, polychaeta).

MOLINA, L.M.; VALIÑAS, M.S.; PRATOLONGO, P.D.; PERILLO, G.M.E.

Bahía Blanca, Argentina

Simposio; ECSA 44 Symposium: Science and management of estuaries and coasts: A tale of two hemispheres; 2008

Estuarine and Coastal Science Asociation

Mesocosm laboratory experiments have been conducted on the effects of bioturbation by the polychaete Laeonereis culveri on the physical properties of estuarine muddy sediments. The aim of this study was to determine the effects of density on this kind of processes. Polychaetes (450 individuals) and muddy sediment (49 corers, 10 cm in diameter and 18 cm in depth) were collected from a high salt marsh in Bahia Blanca Estuary. Sediment columns were placed in a large water container (filled with filtered estuarine water and forced aeration) and were seeded with 5, 10, 15 and 20 individuals, nine replicates, leaving 13 corers without polychaetes as control. The experiment was deployed for a month, after that sediment samples were taken to measure grain size, water content, organic content, chlorophyll a and EPS content. Measurements of sediment stability were made with a Cohesive Strength Meter (CSM). The sediment water content and organic content were higher in the treatment. The sediment chlorophyll a content was higher in the control. The sediment grain size was larger in the treatment, and there were differences between the different densities. The measurements of sediment stability show a high critical shear stress for the control, being the different treatments less stables. The erosion index was higher for the less density treatment and lower for the high density treatment. These results support the hypothesis of a density dependence on the bioturbational effect of L. culveri.Keywords: shear stress, Laeonereis culveri, Cohesive Strength Meter, bioturbation, density dependence