Sediment bioturbation by polychaete feeding may promote sediment stability

Feeding characteristics and burrowing activities of bioturbators can change the dynamic of soft bottoms. The nereidid polychaete Laeonereis acuta (Tre adwell, 1923), is an important component in the intertidal mudflats of the Mar Chiquita coastal lagoon (37 degrees 32'S, 57 degrees 19'W; Argentina). Its feeding mode and burrowing activity were examined in relation between s ediment bioturbation and sediment bedload transport. L. acuta is a deposit feeder that lives in burrows connected to the surface. Burrow depth is rela ted to size, although most worms inhabit the upper 5 cm. Burrows less than 21 mm total length were U-shaped whereas individuals >21 mm in length were found in straight vertical tubes with only one aperture at sediment-water i nterface. The number of sediment mounds produced by L. acuta feeding were c orrelated with their density (1324.16 ind m(-2)), producing up to 57.8 g m( -2) d(-1) of sediment on the surface. Sediments from mounds were coarser, b etter sorted and showed a significantly higher amount of organic matter tha n surrounding bottom sediments. An experiment using bedload traps deployed in a large area dominated by this species showed that the particle size of the sediment from mounds were larger than those transported by bedload. Thi s pattern suggests that cohesive, organically rich sediment deposited at th e surface by polychaete feeding stabilizes the sediment. Under conditions o f low environmental energy, bioturbation by L. acuta may promote sediment s tability.