Secondary production of Chaoborus ceratopogones (Diptera: Chaoboridae) in Lake Bosumtwi, Ghana

Abstract

Preliminary surveys of the zooplankton of Lake Bosumtwi revealed copious amounts of larval stages of Chaoborus ceratopogones in the water column. Secondary production was subsequently determined to assess its role in the zooplankton community. Head capsule length distinguished consecutive larval instars without overlaps. Growth rates were low in instar I and pupae. Instars II and III were the focal points of population growth. Growth equations were used to compute stage-specific biomass and production. Mean larval density was 16,053±15,865 organisms per m3. Daily standing stock varied from 80 to 4180 mg dw m−3 and an annual average production of 920 mg dw m−3 yr−1. Prey biomass was weakly correlated with Chaoborus biomass so most of the variance in Chaoborus production was controlled by mechanisms external to food abundance. Transfer efficiency of Chaoborus production to planktivorous fish may be low because of intense fishing pressure on the lake.