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

Abstract

Production of faecal pellets by the herbivorous estuarine copepodGladioferens imparipes, and the rate at which the pellets sink through a water column, were investigated in the laboratory. Pellet production rate, at excess food concentration, varied among food types, with a maximum rate of 3.2 pellets h ^–1 copepod ^–1 when copepods were fed on the diatom Skeletonema costatum, and a minimum of 1.5 when fed on the chlorophyte Chlamydomonas globosa. Pellet production rates may have reflected feeding prehistory and related effects on food preference and ingestion rates. Settling rates ranged from 2.0 m day ^–1 for pellets produced on the thecate dinoflagellate Scrippsiella sp. to 71.8 for pellets produced on S. costatum. The estimate of settling rate was strongly influenced by the method used to measure it and measure pellet density. Application of the laboratory results to average copepod densities in the Swan River estuary suggested a conservative estimate of production 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 day ^–1 , pellets would easily reach the sediments within a tidal cycle in many parts of the Swan River estuary.