Selection by a deposit-feeding polychaete, Polygordius jouinae, for sands with relatively high organic content
Limnol. Oceanogr., 53(4), 2008, 1512-1520 | DOI: 10.4319/lo.2008.53.4.1512
ABSTRACT: Field observations and flume experiments investigated whether subsurface migration and selection by adult Polygordius jouinae for sediment enriched with organic flocs could help explain small-scale patchiness of this deposit-feeding polychaete in rippled, sandy sediments on the inner continental shelf off New Jersey. Paired ripple crest-trough samples taken from stations located kilometers apart in several months in 1994, 1995, and in May 2006 found higher but more variable densities of P. jouinae in troughs compared with crests. Sedimentary particulate organic matter was also patchily distributed at similar spatial scales. In a racetrack flume under realistic flow (shear velocity = 0.32 cm s-1) and flatbed conditions, arrays of alternating, fresh ambient sediment (including natural levels of particulate organic material) and freshly sieved sediment (reduced in particulate organic content) showed significant subsurface movement of P. jouinae to sediment patches containing higher amounts of particulate organic matter in 48 h. Subsequent experiments showed that locating organic patches was not the consequence of a directed search. However, worms that located richer patches remained there and fed. Rate of movement in sediments indicated that P. jouniae could potentially travel the wavelength of a typical ripple (14-30 cm) at the Long-term Ecosystem Observatory in 15-m water depth in 35-75 min. Thus in a dynamic environment where food concentrations are low and patchy, the affinity of P. jouinae for particulate organic matter and its undirected, high rate of subsurface movement is a plausible mechanism to account for the similar spatial distributions of P. jouinae and its food resources in continental shelf sediments.