Fossil synuracean (Chrysophyceae) scales in lake sediments: a new group of paleoindicators

Abstract

A qualitative examination of the recent sediments of 10 lakes spanning a wide range of limnological conditions indicated that synuracean scales were consistently well preserved in lake sediments. The stratigraphic distribution of the fossil scales of 6 Mallomonas species [M. fastigata, M. crassiquama, M. lelymene, M. allorgei, M. lychenensis and M. reginae] was then studied in the recent sediments of 3 Canadian Shield lakes. Two of these lakes (Found and Jake lakes) are adjacent to a major highway and have been subjected to moderate cultural disturbances. Delano Lake, isolated 4.5 km south of the road, was not subjected to these disturbances and hence was a control. Road construction coincided with the near extinction of M. allorgei in Found Lake, while M. fastigata increased in relative importance in both Found and Jake lakes following cultural disturbances. The Mallomonas standing crop, estimated from the accumulation rate of scales, increased strikingly in Found Lake immediately following the 1933 road construction. No sudden changes in Mallomonas species composition or standing crop were recorded in the control lake''s recent history. Mallomonas taxa may be sensitive to changes in water quality and are therefore potentially useful paleoindicators.