Julius, M. L.. University of Michigan, mjulius@umich.edu
Stoermer, E. L.. University of Michigan, stoermer@umich.edu

 
ONE DIATOM, TWO LAKES: STEPHANODISCUS NIAGARAE POPULATION DYNAMICS RECORDED IN LAKE ONTARIO AND LAKE ERIE SEDIMENTS
 
Stephanodiscus niagarae populations present in sediment cores from Lakes Ontario and Erie show sharp transitions in mean valve diameter and diameter variance. Valve diameter and variance were both relatively stable in these populations from ca. 1850 to 1940 but decreased rapidly after 1940. Temporal patterns in these statistics are highly correlated between populations in the two lakes until approximately 1989. Stephanodiscus niagarae is not present in any post-1989 sediment samples from stations across Lake Ontario. This marks the taxon's extirpation from its type locality. The species may have been directly eliminated from the lake, or sexual reproduction may have been delayed beyond the species' ability to sustain numbers through asexual reproduction. In Lake Erie, S. niagarae populations are present in post-1989 sediments and the decreasing trend in mean valve diameter and variance is reversed in these samples. This reversal is consistent with patterns expected in sexually reproducing populations. This change is coeval with the introduction of Dreissena spp., which has heavily influenced biotic and physical factors in Lake Erie. Introduction of Dreissena, and concomitant increases in transparency, may have prevented the demise S. niagarae populations in Lake Erie.
 
Day: Thursday, Feb. 4
Time: 10:45 - 11:00am
Location: Sweeney Center
 
Code: CS62TH1045S