Freshwater bryozoans (Bryozoa) of Norway II: distribution and ecology of two species of Fredericella

• Published in: Hydrobiologia 2001-09, Vol.459 (1-3), p.103-123
• Main Authors: Oekland, KA, Oekland, J
• Format: Article
• Language: English
• Subjects: Animal and plant ecology; Animal, plant and microbial ecology; Animals; Aquatic plants; Autoecology; Biological and medical sciences; Bogs; Calcium; Ditches; Dystrophic lakes; Elevation; Eutrophic environments; Eutrophication; Fundamental and applied biological sciences. Psychology; Geographical distribution; High temperature; Low temperature; Magnesium; Mountain lakes; Mountain regions; Plant species; Protozoa. Invertebrata; Regression analysis; Sea level; Sediments; Shores; Surface water; Vegetation; Wave action
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1023/A:1012558524160

Freshwater bryozoans were investigated during field studies of 601 lakes and other surface water bodies throughout Norway from 1960 to 1978. The frequency of occurrence of the two Fredericella species was evaluated in relation to 12 environmental variables. Statistically significant deviations from the frequencies expected on the basis of random distribution were described using the categories preference, avoidance and absence. The typical European Fredericella sultana (with glossy statoblasts) occurred at 72 localities, north to 70° 25' N (the northernmost record on a global scale). Its frequency dropped towards the north. Maximum elevation above sea level was 1097 m (maximum recorded for Northern Europe). Another species with pitted statoblasts, tentatively considered to be Fredericella indica, occurred at 50 localities, north to 71° 09' N (the northernmost record reported to date). The geographical distribution reflected a typical northern cold-water species. One third of the 50 records were from lakes situated north of the Arctic Circle, and rich colonies were found on the North Cape plateau, as far north as possible on the European mainland. The few records from southeastern Norway were from high mountain lakes, up to 1397 m above sea level (highest record for Europe). This species was not found in any of the numerous lowland lakes investigated in southeastern Norway where F. sultana was common. Both species tolerated a cold climate, especially Fredericella indica, and they occurred in a wide range of environments. F. sultana preferred lakes with rather low elevation above sea level, rich vegetation with plant species typical for eutrophic environments, gyttja sediments and stony "hard" shores, some wave action, high content of calcium, and slightly coloured water. This species avoided ponds and was absent from ditches and mires, avoided dystrophic lakes surrounded by Sphagnum bog, with dy sediments and strongly coloured water, avoided sites with small wave action, was indifferent to magnesium and low concentrations of calcium, and was absent from lakes with pH below 5.4. F. indica was only recorded from lakes. It preferred rather low temperatures, oligotrophic conditions with poor aquatic vegetation and stony shores, some wave action, pH above 7.0, and low water colour (below 11 mg Pt l^sup -1^). This species avoided lakes with high temperatures and was absent above 20 °C, was absent where aquatic vegetation was rich or consisted of Sphagnum bog, avo