Aspects of feeding, growth and stage development by trochophora larvae of the boreal polychaete Mediomastus fragile (Rasmussen) (Capitellidae)

Abstract

Planktotrophic larvae of the boreal capitellid polychaete Mediomastus fragile (Rasmussen) were hatched and reared to metamorphosis. Larvae were fed Isochrysis galbana and grazing rate, growth and developmental stage were recorded as a function of food concentration, 0–1350 μgC·1 −1. The larvae exhibited delayed stage shifts and reduced growth rates at low food concentrations, <150 μgC·1 −1. Maximum specific growth rate and the maintenance energy requirement were notably low, indicating adaptation to low in situ food concentrations. Larvae were able to capture and ingest particles in the size spectrum between 2 and 10 μm. The optimal particle size was 7 μm. The larvae enter the plankton in the early spring, when the phytoplankton size spectrum is typically dominated by large algal cells, exceeding the size for efficient uptake. The physical limitations for particle capture are therefore a potential limit for grazing. The ability to delay larval development is an advantage for a planktotrophic larva functioning as a growing dispersive organism.