Cycle characteristics of planktonic cladocerans in a tropical lake, Central Amazon: Field and experimental work

Abstract

This thesis is concerned with an investigation into the effects of food concentration, temperature and turbidity on the life cycle characteristics such as growth, body size, development and reproduction of species of planktonic Cladocera brought to the U.K. from a shallow turbid Lake Jacaretinga, Amazonia. The species studied were Daphnia gessneri, Moina reticulata and Diaphanosoma sarsi. Long term growth experiments were performed using both batch and continuous flow culture under controlled laboratory conditions using various combinations of temperature (22°, 27°, and 32°C),concentration of algal food Scenedesmus acutus (0.03, 0.05, 0.1, 0.25, 0.5, and 1.OmgC.1) and turbidity (10, 20, and 50 NTU). Animals were examined daily throughout their cycle from the newborn (neonate) to 3rd adult instars.The ecology of planktonic animals in Lake Jacaretinga was studied intensively during a three month period (February, March and April 1986). This period of study included two ecologically/limnologically important periods, namely, before the flooding of the River Amazon and after the river flooding, when the lake became more turbid due to suspended particles. Weekly samples of zooplankton providedinformation on the species composition and numerical density of the cladoceran populations as well as their horizontal distribution in five stations. Information was also obtained on environmental condition in the lake (Temperature, dissolved oxygen concentration, Secchi disc transparency, chlorophyll-a and particulate carbon concentration.Population of Diaphanosoma sarsi, Ceriodaphnia cornuta and Daphniagessneri, decreased during the flood, and populations of Moinareticulata increased and became a dominant species. Life cycle experiments shows that growth and reproduction are greatly influenced by food concentration and turbidity. Consistent differences were found between Daphnia gessneri and Moina reticulata,being Moina reticulata more successful in survival, growth and reproduction. Application of the experimental results on the effects of food, temperature and turbidity on the life cycle characteristics of the planktonic cladocerans are used to interpret the changes in the cladoceran population in Lake Jacaretinga during this period of floading. This is a significant contribution to our knowledge since Lake Jacaretinga is one of the characteristic varzea lakes in Central Amazonia whose limnology is largely determined by the annual flooding of Amazon River.