Abstract:
Plankton samples were collected using plankton nets to examine the phytoplankton and zooplankton
community dynamics in two streams: namely, Mahaoya, and Panajjawa Oya and two lakes: namely,
Bubula Lake and Wagaspitiya Lake in Mahaoya, Ampara district, Sri Lanka. The samples were
collected in two consecutive periods in May and August 2011.
Aplocheilus dayi and Rasbora daniconius, two naturally occurring fish species were collected (n=50)
using cast nets to examine their food aspects in absence of Anopheles mosquito larvae in May 2011
and in their presence in August 2011. Of the total plankton community, only about 28% (14 species)
represented zooplanktons while 72% (55 species) were phytoplanktons. Total 14 zooplankton species
belonged to; Class Branchiopoda (5 species); Class Lobosa (1 species); Class Maxillopoda (4
species); and Class Monogononta (4 species), and 55 species of phytoplankton population belonged to
Class; Chlorophyta (24 species); Class Cyanophyta (11 species); Class Bacillariaphyta (10 species);
Class Ochrophyta (4 species); Class Euglenophyta (4 species); Class Heterokontophyta (2 species).
The zooplankton population of two streams was dominated by Chromogaster spp. (40 - 80 /ml) while
that of two lakes, Bubula and Wagaspitiya were dominated by Eucyclops spp.(120/ml) and Cyclops
spp. (80/ml) respectively. The phytoplankton population in all the four water bodies was dominated
by Closterium spp. (200-400/ml).
The above data reveals that the phytoplankton diversity in two lakes is greater (total of 26
species/taxa) than that of two streams (total number of 14 species/taxa) but, there was no difference in
zooplankton diversity between the two habitats. Density and diversity of both phytoplankton and
zooplankton in each site between two consecutive sampling occasions (soon after heavy rains in
absence of mosquito larvae and during the dry spell in presence of mosquito larvae) did not vary
significantly. Gut analysis of two naturally occurring fish species, Aplocheilus dayi and Rasbora
daniconius revealed that both of their diets mainly composed of crustaceans 40%, insects 35% and
algae, detritus, diatoms and plant parts 25% by number, in presence of mosquito larvae in the habitats
in August 2011.
