Distribution and summer diapause of Canthocamptus staphylinus (Jurine) (Copepoda: Harpacticoida) in Lake Ladoga
The spatial distribution of Canthocamptus staphylinus (Jurine) in Lake Ladoga was examined. C. staphylinus is one of the most numerous species of harpacticoids in the lake. It can dwell in almost all littoral biotopes. In profundal biotopes strongly exposed to anthropogenic influence (pollution and eutrophication) only this species of harpacticoid was found. A peculiarity of C. staphylinus biology is that in summer individuals are in the resting stage as cysts. In summer active individuals were found in littoral habitats at a water temperature of 20 °C, but their number was small in comparison with cold periods of the year. In the littoral zone the relative number of individuals in cysts was clearly related to water temperature. Twelve degrees temperature appears to be critical for development of littoral populations of C. staphylinus.
Effects of eutrophication and organic loading on the occurrence of profundal harpacticoids in a lake in southern Finland
Harpacticoids made up 19 and 30% of the meiobenthos proper by number and 39 and 55% by biomass at maximum depths and a depth of 20 m, respectively, in Lake Päijänne. Harpacticoids accounted for higher proportions of the total meiobenthos in oligotrophic and unpolluted areas than in polluted areas. Seven species were identified, with Canthocamptus staphylinus confined to semi-lotic areas influenced by organic pollution from a pulp mill. Other species exhibited somewhat different distributions in oligotrophic and mesotrophic areas. Harpacticoid densities were most closely correlated with oxygen content and phytoplankton biomass, and correlations with environmental values were closer at maximum depths than at 20 m. Attheyella crassa densities in the deepest zone had most marked negative correlation with total phosphorus, phytoplankton biomass, dissolved organic matter and organic sedimentation, while Paracamptus schmeili had the closest positive correlation with oxygen content. High densities of these species could be classified as an indicator of oligotrophic conditions. Similar correlations, although weaker, were evident for Bryocamptus minutus and still weaker for Bryocamptus echinatus and Moraria brevipes. Clustering of the stations based on harpacticoid abundances gave a similar result to clustering based on environmental data, particularly in the 20 m zone.
Sexual Reproduction in Copepods
AMONG the lower groups of Crustacea, namely, the phyllopods, cladocera and ostracods, parthenogenesis is a well-known phenomenon and in many cases it is the only one known by which reproduction takes place. It is therefore remarkable that the process has only been recorded once within the free-swimming copepods1.