Temperature and food as factors affecting the population ecology of Bosmina longirostris (O. F. Muller, 1785) and Diaphanosoma brachyurum (Lieven, 1848)

The survival and reproduction of Bosmina longirostris and Diaphanosoma brachyurum (Cladocera) were investigated through feeding experiments with three algae and four different temperatures. The live samples were collected from the Gunston Cove area of the tidal freshwater Potomac River with a 202mu mesh conical net via a tow. Parameters examined were: (1) individual response to three food concentrations of three algae: Ankistrodesmus falcatus var. acicularis, Cyclotella meneghiniana and Micrucystis aeruginosis; (2) individual response to four temperatures: 10, 15, 20 and 25°C; (3) response to temperature with both cladocerans combined using 1:8, 2:6, 3:4 and 4:2 (ratios of Diaphanosoma to Bosmina) treatments at temperatures of 10, 15, 20 and 25°C. Results of the experiments showed that the population growth rates (rm) varied with food concentrations and food type for both species with generally positive responses to increasing food concentration in Ankistrodesmus and Cyclotella and a negative response to Microcystis. In the individual temperature treatment, the rm values for Bosmina increased from 10--20°C but decreased at 25°C. The rm values of Diaphanosoma increased with temperature reaching a maximum in 25°C. Results indicate a difference in temperature optima for the two cladoceran species which helps explain their coexistence in Gunston Cove.