Abstract:
Vertical distribution of cyclopid copepcds was studied in Kotmale reservoir,
in order to determine the variation in zooplankton at different depths. Their
seasonal distribution and migratory patterns were also studied.
Vertical and horizontal sampling were done at monthly intervals from
August 1990 to December 1991. Two diurnal samplings were done; one
when water level was low (40m) and the other when it was high (62m).
The two cycIopid species identified were Mesocyclops leukarti and
Thermocyclops crassus.
CycIopid adults and their immature stages were abundant at all depths.
However their population density decreased with increasing depth. Highest
density was found within the range of surface to ten meters.
They showed striking diurnal migration which was independent of the
intensity of sunlight. The migratory pattern of adults and young was not
much different.
The seasonal variation observed did not show the same pattern during
both sampling years. During the latter part of the study (October to December
1991)a large decrease in cyclopid population was observed which was correlated
with the collapse of green algae population and the appearance of algal bloom
caused by blue green algae (Microcystis aeruginosa).
