Stoermer, E. F. University of Michigan, stoermer@umich.edu
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DIATOM SPECIES REACTIONS TO SILICA DEPLETION IN THE GREAT LAKES
 
Diatom species reacted differently to reductions in biologically available silica, resulting from phosphorus pollution, in the Great Lakes. The relative impact was highly related to individual species, or species associations, adaptations to particular temporal and physical habitats. In general, planktonic species most abundant during winter circulation increased relative to summer-blooming populations, even those which inhabit the sub-thermocline abundance maximum. The latter were largely extirpated from lakes Erie and Ontario, returning only after transparency increases due to the zebra mussel (Dreissena spp.) invasions. Tychoplanktonic species generally became more important relative to euplanktonic species. Winter-blooming populations increased following initial reductions in dissolved silica levels then declined as silica limitation became more severe. Summer-blooming populations, usually restricted to areas shallow enough to be circulated by wind stress in summer, increased and remained abundant even when dissolved silica was near analytical zero. It appears that a large number of species have been extirpated from the Great Lakes and a somewhat smaller number of exotics have successfully invaded. Extirpation was most drastic among rich benthic communities once abundant to depths < 30 m, although some characteristic plankton populations have been lost. Most successful invaders are salinity and eutrophication tolerant euplanktonic species.
 
Day: Friday, Feb. 5
Time: 03:45 - 04:00pm
Location: Sweeney Center
 
Code: SS13FR0345S