The impact of population abundance on the deposit-feeding rate of a cosmopolitan polychaete worm

Abstract

The impact of population abundance on the deposit-feeding rate of Mediomastus ambiseta (Capitellidae: Polychaeta) was studied in still-water laboratory experiments. Mean individual pellet production rate (mg worm-1 d-1) decreased monotonically with increasing worm abundance in the range of 6.5 x 103 to 1.3 X 105 worms m-2. Worms fed roughly an order of magnitude slower in the high-density treatment than in the low-density treatment. The vertical distribution of pellets (i.e., sites of egestion), however, was insensitive to changes in worm abundance. Despite the high population abundances, the weight-% of pellets in the highest abundance treatments was <20%. Therefore, contrary to expectations, it was unlikely that feeding rate was limited by the availability of ingestable particles. Rather, some combination of resource depletion and possibly of enhanced physical or chemical interference caused the observed decline in feeding rate at higher population abundances. These results suggest that studies that seek to transfer laboratory-based measures of deposit-feeding rate to the field must be careful to match abundances in the two domains.