House production by Oikopleura dioica (Tunicata, Appendicularia) under laboratory conditions

Abstract

We examined the generation time and the house renewal rate of Oikopleura dioica under various conditions. Animals were fed two flagellates, Isochrysis galbana and Tetraselmis sp., with concurrent determination of the carbon contents of body and house to estimate house production. The generation time was 6 days at 15°C, 4 days at 20°C and 3 days at 25°C at both 25 and 30 p.s.u. with a food concentration of 4 × 104 cells ml-1. The carbon content of newly secreted houses ranged from 0.5 to 0.8 μg, corresponding to 15.3 ± 4.8% of body carbon. The house renewal rates increased with increasing temperature and decreasing salinity. Food concentrations ranging from 100 to 16 × 104 cells ml-1, body size and light condition had no effect on house renewal rate. Clogging of the inlet filter by adding the large diatom Ditylum sol caused an increase in house renewal rates. The total number and carbon content of houses during an animal's lifetime ranged from 46 to 53 houses and from 6.5 to 10.4 μg, respectively. Since daily house production calculated for the O. dioica population corresponded to 130-290% of its biomass and daily discarded house materials corresponded to 490-1100% of the biomass, this organism must play an important role as a producer of macroscopic aggregates.