Comparative physiological energetics of two suspension feeders: polychaete annelid Lanice conchilega (Pallas 1766) and Pacific cupped oyster Crassostrea gigas (Thunberg 1795)

Abstract

Feeding competition between the Pacific cupped oyster Crassostrea gigas and the polychaete Lanice conchilega was studied by assessing the polychaete suspension feeding activity. Retention efficiency was estimated by comparing particle size distributions at the output of experimental chambers containing the species and controls. Although particles ranging from 4 to 12 μm were collected by L. conchilega, no upper threshold or maximum retention rate was reached within this range. In contrast, C. gigas showed retention starting at 2 μm, and reaching an upper threshold at 6 to 8 μm. Based on our results, feeding competition is likely to occur between C. gigas and L. conchilega. Standardised filtration rates reached 0.225 l h −1 g dmw −1 (±0.08) for L. conchilega and 2.43 l h −1 g dmw −1 C. gigas for animals of 1 g dry meat weight (dmw). Assimilation rates, 0.44 for L. conchilega and 0.49 for C. gigas, were similar for the two species. Respiration rates were estimated at 0.113 and 0.68 ml O 2 h −1 for L. conchilega (Allometric coefficient=0.534) and C. gigas respectively. Therefore polychaete scope for growth (SFG) (4.01 J h −1 g dmw −1) was significantly lower when compared with C. gigas SFG (61.96 J h −1 g dmw −1). The impact of the L. conchilega population on that of cultivated oysters was evaluated from these results and field population assessment of both species. Based on field population estimates, L. conchilega was responsible for a 19% decrease in the carrying capacity and 30% of the oxygen depletion from the total activity of both species. However, L. conchilega SFG was only 16% of that of the C. gigas population. Several hypotheses regarding population interactions are discussed.