Active post-settlement habitat selection for fine organic flocs, by a deposit-feeding polychaete, Polygordius jouinae, in a laboratory flume under still water and flow conditions.

Understanding the relationship between infaunal organisms and the sedimentary habitats in which they live is critical to the prediction of ecological responses to long-term habitat changes on continental shelves. Macrofaunal surveys at LEO-15 show the deposit-feeding marine worm, P. jouinae, is commonly found in much higher densities in ripple troughs compared to crests in sands. Using a laboratory flume under flow and flat bed conditions we tested whether this pattern could be causally related to active selection by the worm for fine organic flocs typically associated with troughs. In a racetrack flume, arrays of alternating fresh sediment from LEO-15 (+organic floc treatment) with freshly sieved  sediment (-organic floc treatment), showed significant subsurface movement of P. jouinae to sediments containing higher amounts of organic flocs (+ organic floc) in 48 h. Selection for  +organic flocs did not depend on floc location in relation to flow direction (downstream vs upstream). Subsequent experiments showed that initial movement of P. jouinae is best described as random, but worms that locate food patches remain there.