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Presented at the NABS Annual meeting, La Crosse, Wisconsin, 2001
INVADING SPECIES DOMINATE THE HARPACTICOID FAUNA IN NEARSHORE SANDS OF SOUTHERN LAKE MICHIGAN
T. G. Horvath, E. J. Oberdick, L. L. Last, and R. L. Whitman. U. S. Geological Survey, 1100 N. Mineral Springs Road, Porter, Indiana 46304, USA
Harpacticoids (Copepoda: Harpacticoida) are important components of aquatic communities; however, they often are overlooked in studies of the Laurentian Great Lakes. We sampled psammic habitats of southern Lake Michigan >1 km offshore at different depths (1-15 m) from 1996 through 2000. We documented two harpacticoid species new to the Great Lakes: Schizopera borutzkyi Montschenko (introduced species) and Heteropsyllus sp. A (undescribed species). S. borutzkyi is native to the Danube River delta (Black Sea), and Heteropsyllus sp. A represents the first occurrence of this genus in freshwater. We consider both species to be recent invaders, based on their absence in previous studies. Combined harpacticoid abundance was low (0-5000 ind./m2) and differed by depth (p <0.05). Abundance was generally greater at deeper depths, but individuals occasionally were collected from shallow sands (< 5/m2 from 1 to 4 m deep). Invading species always greatly outnumbered native species; Heteropsyllus sp. A tended to dominate (55-100%) the harpacticoid abundance to depths of 9 m, whereas S. borutzkyi was most dominant (55-76%) at 15 m. The ecological effects of these introductions are not known, but these invaders are altering the species composition of nearshore communities in Lake Michigan.
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