Establishment of two invasive crustaceans (Copepoda : Harpacticoida) in the nearshore sands of Lake Michigan

Benthic copepods (Copepoda: Harpacticoida) in the nearshore sediments of so uthern Lake Michigan appear to be dominated by two new invasive species. We report the first occurrence in North America of Schizopera borutzkyi Monts chenko, a native to the Danube River delta, and Heteropsyllus nr. nunni, li kely a new species that is morphologically similar to the marine species He teropsyllus nunni and represents the first occurrence of this genus in fres hwater. Schizopera borutzkyi is a euryhaline species occurring in shallow s ands in its native habitat and in deeper sands (6-15 m) in southern Lake Mi chigan. Based on the absence of these species from previous studies, we sug gest that they are recent introductions. Heteropsyllus nr. nunni dominated (55-100%) the harpacticoid abundance to depths of 9 m, but S. borutzkyi com prised 75% of the harpacticoid abundance at 15 m. Native harpacticoids were always greatly outnumbered by invasive harpacticoids in our samples, which suggests that the natives are being replaced rapidly or that the invasive species are finding unused resources. The ecological implications of these introductions are not known, but these invasions may represent continued "i nvasional meltdown" in Lake Michigan.