THE ACTIVITY OF NEREIS-DIVERSICOLOR (POLYCHAETA) AND ITS IMPACT ON NUTRIENT FLUXES IN ESTUARINE WATERS

Seasonally and spatially varying populations of the polychaete Nereis diversicolor have been studied at three sites in the estuary of the River Tamar, south west England. Undisturbed cores from each of these sites, and from a fourth site devoid of this species, were incubated in the laboratory on each of six dates between December 1990 and May 1992 for sediment-water exchange studies. The fluxes of soluble ammonium and silicate were shown to be up to 100 times greater than those calculated from pore-water concentration gradients, and to be related to the extent of burrow surfaces as estimated from the population parameters of the worms recovered from the cores. Cores with the most worms (up to 5000 per m(2)) had burrow surfaces areas equivalent to between 200 and 300% of the unburrowed interface. This scale of increase was insufficient to fully explain the magnitude of the fluxes which are further enhanced by irrigation of the burrow surfaces, causing nutrient-enriched pore waters diffusing through burrow walls to be flushed into the water column. It is calculated that over the whole of the Tamar estuary, N. diversicolor populations could account for fluxes to the water column of between 10 and 20 times the measured inputs of soluble ammonium derived from riverine and sewage sources.