The influence of benthic tundra pond vegetation and prey behavior on Zooplankton predation by the flatworm Mesostoma lingua

Experiments were conducted at the Smoking Hills and Tuktoyaktuk, N.W.T., to determine if Mesostoma lingua, a common pond inhabitant, preys selectively on co-occurring Zooplankton, and whether predation rates are affected by the presence of pond vegetation. Experiments were conducted in 250-mL containers at the sites. Mesostoma fed heavily on Daphnia pulex and Chironomus riparius, but not on Branchinecta paludosa or Diaptomus arcticus. The presence of alternative prey led to significant reductions in Daphnia predation rates, while the presence of the pond plants Cladophora insignis and Drepanocladus aduncus, which provide shelter and cover, significantly increased predation rates. The advantage of the moss and algal habitat was largely to the predator.

Erratic occurrence of anostracans in a temporary pond: colonization and extinction or adaptation to variations in annual weather?

Five species of Anostraca (Branchinecta paludosa (O.F.M.), Branchinecta lindahli Packard, Eubranchipus bundyi Forbes, Eubranchipus intricatus Hartland-Rowe, and Eubranchipus ornatus Holmes) inhabited a temporary pond near Calgary, Alberta. During a 14-year study of this pond, occurrence and species composition of anostracans changed almost every year. In most years only one to three species were common or abundant, and the other species were either absent or rare. Four of the five species were dominant in at least 1 year. A review of literature on anostracans and analyses of annual weather patterns at Calgary were carried out in order to determine the cause of these erratic occurrence patterns and changes in species composition. For Eubranchipus bundyi, Branchinecta lindahli, and possibly Eubranchipus intricatus, the cause was probably due to long-term viability of eggs in association with species specific requirements of the embryo for certain quantities of precipitation at critical times of the year. It is suggested that when these precipitation requirements were ideal, hatching was substantial. For two other species, Branchinecta paludosa and Eubranchipus ornatus, erratic occurrence patterns could be explained by either the above or by a colonization–extinction hypothesis.

On the distribution and biology of an arctic fairy shrimp Artemiopsis stefanssoni Johansen, 1921 (Crustacea: Anostraca)

The distribution of Artemiopsis stefanssoni is described. Samples from eight localities in Baffin Island and Somerset Island were analysed and showed wide variations between populations in body size and egg production. These variations probably correspond to variations in food availability. Maximum lengths recorded were 9.00 mm for males and 11.95 mm for females. The egg sac of this species has no genital opening. Successive clutches are retained within the egg sac instead of being released after fertilisation and deposition of the tertiary shell. Egg sacs contained up to 120 eggs, whereas maximum ovary output was 40 eggs per clutch. It is suggested that retention of eggs within the egg sac affords protection against egg predation by benthic feeders such as Branchinecta paludosa and Lepidurus arcticus.