Bryozoan statoblasts in the recent sediments of Douglas Lake, Michigan

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 210Pb 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-1 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 had 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.     

Freshwater bryozoans of New Zealand: A preliminary survey

Five bryozoan species were encountered in a 15‐day survey of freshwater habitats in New Zealand. Listed in order of decreasing frequency these were: Fredericella sultana, Plumatella repens, P. emarginata, Paludicella articulata, and one plumatellid species not previously described. Micro‐structural features of the floatoblast annulus separate the P. repens specimens into two distinct varieties, named here P. repens typica and P. repens rugosa. Paludicella, reported almost 100 years ago from the City of Dunedin waterworks, was still found only in a single reservoir of that city. Species distribution did not correlate significantly with water temperature, current velocity, pH, or total dissolved solids. Two additional species believed to occur in New Zealand, Fredericella australiensis and Plumatella fungosa, were not seen in this brief survey. An identification key is provided for New Zealand bryozoans.