Bryozoan statoblasts in the recent sediments of Douglas Lake, Michigan

TitleBryozoan statoblasts in the recent sediments of Douglas Lake, Michigan
Publication TypeJournal Article
Year of Publication1997
AuthorsFrancis DRuth
JournalJournal of Paleolimnology

Statoblast valves produced by the freshwater bryozoan Plumatella nitens were recovered in three sediment cores from Douglas Lake, Michigan. Douglas Lake is a multi-depression lake of glacial origin. The region was heavily logged from 1880 to 1920. sediment cores were taken from three of the seven depressions, and dated using 210 Pb isotopes and pollen. Sedimentation rates were very low in the Grapevine Point core as compared to the other two cores. Concentrations of statoblasts ranged from three to 140 ml/l of wet sediment. Profiles of statoblast concentrations and accumulation rates indicate a sharp decline in Plumatella populations corresponding to the time the Douglas Lake watershed was being clear-cut. It appears that logging and the resulting increase in erosion has adverse effects on bryozoan populations, and possibly on the entire littoral zone of the lake. High sediment loads to the lake could have caused mortality in Plumatella by interfering with the feeding of these animals, or by decreasing numbers of macrophytes which are frequently used as substrate. Populations of Plumatella have not recovered to pre-disturbance levels.