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.

Keywords:

• Diptera
• Chaoborus
• secondary production
• tropical
• Lake Bosumtwi

Acknowledgements

This research is part of collaborative work between the Biology Departments of the University of Waterloo (UW), Canada and Kwame Nkrumah University of Science and Technology (KNUST), Ghana which was financed by Natural Sciences and Engineering Research Council of Canada (NSERC) Special Research Opportunities grant with supplementary support from KNUST Staff Development Programme. Department of Foreign Affairs and International Trade (Canada) through its Commonwealth Graduate Student Exchange programme supported P.O Sanful for 1 year fellowship activities at UW where analyses of field samples were carried out. The authors acknowledge consecutive SIL Tonolli Memorial Fellowship awards to P.O Sanful. Prof. S.K Danuor, Mr Fredua Agyeman, John Bilson, Yaw Manu and “Ice Water” all assisted with field work. Prof. Nils Ekelund hosted P.O Sanful at Mid Sweden University and Swedish Institute Guest Scholarship Programme funded the research activities at Mid Sweden. Prof. W.D Taylor and Prof. W. M Lewis Jr provided continued guidance throughout the research with the latter critically reviewing the manuscript. Dr Megan Otu and Dr Francis E. Awortwi were involved in the collaboration and assisted this research in various ways.