Branchinecta

Abstract: Two distinct communities exist in a series of small subalpine ponds on Galena Mountain, Colorado, at 3,400 m. In the deep ponds, two predators, the culicid larva Chaoborus and the axolotl Ambystoma tigrinum, coexist with two small herbivores, the copepod Diaptomus coloradensis and the cladoceran Daphnia rosea. In the shallow ponds the predatory salamander (Ambystoma tigirinum) coexists with three large herbivores, Daphnia pulex, Diaptomus shoshone (which may be predatory as an adult), and the fairy shrimp, Branchinecta shantzi, as well as the small Diaptomus coloradensis. Despite the proximity of deep and shallow ponds, each community has remained resistant to invasion from the other for at least 5 years. To determine why, I recorded the survival of organisms placed in cages in foreign ponds alone and in combination with the native species. Results revealed that chemical or physical conditions were limiting only for Daphnia pulex, which did not survive well in deep ponds. The large Diaptomus shoshone and ...

Abstract: Observations on populations of Branchinecta mackini in temporary ponds, which last for as little as 3 days to as long as 4 months, on a desert playa showed that hatching of dehydrated cysts (eggs) follows initial entry of water into the basin if salinity remains low. Salinity ranges from an initial 0.5% to as much as 34% as the pond evaporates. Hatching is continuous at constant low salinity, but since salinity general increases rapidly, initial hatch is usually of short duration. Additional periods of hatching follow further inflows of water or after meeting of ice, that is, after reductions in salinity. The duration of hatching is inversely proportional to rate on increase in salinity. When salinity of small—volume summer ponds increases at rates above 500 ppm (1,000 (mu)mhos) per day, three in virtual inhibition of hatching. Laboratory studies showed that egg hatching was controlled by both salinity and oxygen operating in various combinations to inhibit or stimulate hatch. The hatching characteristics...

Abstract: Experiments were performed in 1977 to determine which large zooplankton in a series of high altitude ponds can be consumed by the predatory flatworm Mesostoma ehrenbergii. This predator consumes Daphnia at a high rate and the fairy shrimp Branchinecta at a low rate, but does not consume Diaptomus. Experiments were performed in 1978 and 1979 to determined the rate of predation on Daphnia in 30 liter tubs and to determine if predation rate is correlated with surface to volume ratio of experimental containers. There is a clear correlation between surface to volume ratio and predation rate. Determinations of Mesostoma and Daphnia densities were made in a series of eight high altitude ponds, and pond surface to volume ratios were determined. Examination of these parameters lends credence to the argument that Mesostoma predation affects Daphnia dynamics in some circumstances. The results suggest that benthic invertebrate predators may affect zooplankton dynamics, especially in shallow ponds.