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

We examined the generation time and the house renewal rate of Oikopleura di oica under various conditions. Animals were fed two flagellates, Isochrysis galbana and Tetraselmis sp., with concurrent determination of the carbon c ontents of body and house to estimate house production. The generation time was 6 days at 15 degreesC, 4 days at 20 degreesC and 3 days at 25 degreesC at both 25 and 30 p.s.u. with a food concentration of 4 x 10(4) cells ml(- 1). The carbon content of newly secreted houses ranged from 0.5 to 0.8 mug, corresponding to 15.3 +/- 4.8% of body carbon. The house renewal rates inc reased with increasing temperature and decreasing salinity. Food concentrat ions ranging from 100 to 16 x 10(4) cells ml(-1), body size and light condi tion had no effect on house renewal rate. Clogging of the inlet filter by a dding the large diatom Ditylum sol caused an increase in house renewal rate s. The total number and carbon content of houses during an animal's lifetim e ranged from 46 to 53 houses and from 6.5 to 10.4 mug, respectively. Since daily house production calculated for the O. dioica population corresponde d to 130-290% of its biomass and daily discarded house materials correspond ed to 490-1100% of the biomass, this organism must play an important role a s a producer of macroscopic aggregates.