The effects of crude oil on the population structure of plankton

The effects of crude oil on the population structure of plankton in water samples collected from a fish pond at the African Regional Aquaculture Centre, Aluu, was investigated for a period of four weeks. The samples were analyzed initially for species composition, community structure, population density and water quality. The samples were divided into five different tanks after which crude oil was introduced into the test tanks. The data showed that exposure to crude oil significantly reduced the population density of the plankton, altered the species composition, community structure and some of the water quality variables in the experimental tanks. In the control, pH values dropped from 6.61 to 6.05 in the 1.0 and 2.0ml/L tanks respectively. Oxygen values decreased from 7.5 to 5.78 in the control and to 5.34 and 5.16 in the 1.0 and 2.0ml/L tanks respectively. Temperature values were relatively stable in all the tanks. Exposure to crude oil caused a reduction in the number of phytoplankton genera from 19 to 12 and from 19 to 11 in the 1.0 and 2.0ml/L tanks respectively. Similarly, zooplankton genera decreased from 8 to 5 in the 1.0ml/L tank but increased from 8 to 9 in the 2.0ml/L tank. The genera eliminated by the crude oil include Cosmarium spp, Euglena and Navicula dicephela. The effects of crude oil on plankton therefore are tied to the amount of crude oil spilled