Freshwater bryozoans (Bryozoa) of Norway III: distribution and ecology of Plumatella fruticosa

• Published in: Hydrobiologia 2002-07, Vol.479 (1-3), p.11-22
• Main Authors: Okland, KA, Okland, J
• Format: Article
• Language: English
• Subjects: Alkaline water; Animal and plant ecology; Animal, plant and microbial ecology; Animals; Aquatic plants; Autoecology; Biological and medical sciences; Brackish water; Calcium; Cold regions; Distilled water; Ectoprocta; Eutrophic environments; Eutrophication; Fundamental and applied biological sciences. Psychology; Lakes; Magnesium; Plumatella fruticosa; Protozoa. Invertebrata; Sea level; Surface water; Vegetation
• ISSN: 0018-8158; 1573-5117
• DOI: 10.1023/A:1021060027225

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 Plumatella fruticosawas 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. According to our material P. fruticosais one of the most common bryozoan species in Norwegian fresh water, represented in samples from 251 localities. This species occurred frequently all over the country, north to 71° 06' N (the northernmost record globally). Maximum elevation above sea level was 1179 m (maximum for Northern Europe). In most studies of freshwater bryozoans from the holarctic region, Plumatella fruticosahas been reported as widely distributed, but locally rare. In Norway, however, P. fruticosa is frequently found all over the country, even far to the north. The species apparently finds an optimal climate in the cold temperate and cold regions of Norway. Plumatella fruticosapreferred lakes, avoided slow-flowing rivers and ponds, and was absent in smaller water bodies. The species preferred somewhat higher elevation (400-900 m above sea level), but avoided lakes with the lowest summer temperatures (below 11 °C). P. fruticosa also preferred oligotrophic conditions with poor aquatic vegetation, stony shores, lakes poor in calcium and magnesium (sometimes almost comparable with distilled water), where the water was clear and colourless, and slightly acidic to neutral. The species also preferred lakes surrounded by Sphagnum bogs and was absent when pH was below 5.2. P. fruticosa avoided eutrophic conditions with rich aquatic vegetation, alkaline water (pH above 7.0), lakes with a higher content of calcium and magnesium and those with strongly coloured water (above 100 mg Pt l^sup -1^). In spite of its preference for ion-poor conditions, it was also found in a brackish water lake. For most environmental variables, the species had a wider tolerance range than reported from elsewhere.[PUBLICATION ABSTRACT]