Growth, Consumption and Respiration by Larvae of the Kelp-Fly Fucellia Capensis (Diptera:Anthomyiidae)

Abstract

At 18 °C the eggs of the kelp-fly, Fucellia capensis, hatch in 24 – 32 h and the larval and pupal stages last 10 – 12 and 9 – 14 days respectively. The growth curve is discontinuous, with declining relative growth rates in successive larval instars. Food consumption is relatively independent of size, at 0,25 mg dry kelp mg^-1 wet larva day^-1. Respiration rate is related to larval mass by the equation: Respiration rate (μl O₂ h^-1) = 2,75 (wet mass larva)^0,66. In terms of energy an individual larva consumes 245,5 J over its lifespan, grows to the equivalent of 43,9 J and respires 51,6 J, indicating an assimilation efficiency of 30% and a gross growth efficiency of 17%. Kelp-fly larvae are probably less significant consumers of drift kelp than amphipods or isopods, but they promote the decay of wrack beds and are favoured as food by sea-shore birds.