Influence of food type on the production and settling rate of faecal pellets produced by an estuarine copepod

Production of faecal pellets by the herbivorous estuarine copepod Gladiofer ens imparipes, and the rate at which the pellets sink through a water colum n, were investigated in the laboratory. Pellet production rate, at excess f ood concentration, varied among food types, with a maximum rate of 3.2 pell ets h(-1) copepod(-1) when copepods were fed on the diatom Skeletonema cost atum, and a minimum of 1.5 when fed on the chlorophyte Chlamydomonas globos a. Pellet production rates may have reflected feeding prehistory and relate d effects on food preference and ingestion rates. Settling rates ranged fro m 2.0 m day(-1) for pellets produced on the thecate dinoflagellate Scrippsi ella sp. to 71.8 for pellets produced on S. costatum. The estimate of settl ing rate was strongly influenced by the method used to measure it and measu re pellet density. Application of the laboratory results to average copepod densities in the Swan River estuary suggested a conservative estimate of p roduction of 360 pellets L-1 day(-1), or 8 g C and 1 g N, given appropriate food conditions. With a conservative estimate of settling rate at 6.3 m da y(-1), pellets would easily reach the sediments within a tidal cycle in man y parts of the Swan River estuary.