Toledo Harbor (Maumee River and Maumee Bay) is a “port of concern” for introduction of non-indigenous species into the Great Lakes due to the large amounts of ballast water from outside the Great Lakes discharged at the port, the amenable habitat for many potential invasives, and the large amount of ballast water transported from Toledo to other Great Lakes ports, making Toledo a potential source of invasives throughout the entire region. To estimate sampling intensity needed to detect rare or new non-indigenous species, 27 benthic grab samples from 13 locations near Toledo Harbor were collected during autumn, 2010. Benthic organisms were identified, and sampling intensity needed to detect rare or new non-indigenous species was evaluated via a Chao asymptotic richness estimator. Morphological taxonomic criteria and cytochrome oxidase I (COI) sequence barcodes identified 29 different taxa (20 to species level) in the samples, including six non-indigenous taxa (Branchiura sowerbyi, Bithynia tentaculata, Corbicula fluminea, Dreissena polymorpha, Dreissena bugensis, Lipiniella sp.). While all the non-indigenous species had previously been reported in Lake Erie or nearby Ohio waters, several North American species are not previously listed in Ohio. Richness estimates indicate that >75% of the benthic species in the area were encountered and that 90% of the species could be detected with less than a doubling of collecting effort. Since sampling for this study occurred only in the autumn and detectable life stages of benthic organisms may vary seasonally, additional species may be observed with more extensive sampling over a broader seasonal range.
Dreissenids are invasive bivalves, native to water bodies of the Ponto-Caspian region of southwestern Asia. Following dispersion in Europe in the early nineteenth century, they were accidentally introduced into the Great Lakes region of North America in the 1980s and 1990s. Recently, they were discovered in the southwestern USA. Initially, Dreissena polymorpha (zebra mussel, ZM) spread more rapidly than Dreissena rostriformis bugensis (quagga mussel, QM); however, QM is becoming predominant in many areas of the Great Lakes and was the first to appear west of the Continental Divide, in Lake Mead. In Europe, as well, ZM was the first species to spread widely in western Europe from its endemic range; however, QM have recently been found in areas previously colonized only by ZM. This article reviews the dynamics of this double dreissenid invasion and considers the question: what mechanisms mediate the displacement of ZM by QM? Despite their similar appearance, QM differ from ZM in temperature and salinity tolerance, byssal thread attachment, growth, respiration rates, assimilation efficiency, enzymes such as thiaminase, depth of occurrence, and reproduction. Differences in reproduction include the depth at which reproductively active animals are found, the temperature at which spawning can be initiated, number of gametes produced, and length and timing of their annual reproductive cycle. A hypothetical role of hybrids between the species mediating species change is suggested. Future investigations of the displacement of ZM by QM should consider the role of reproductive differences (hybrids, responses to environmental chemicals, etc.) in mediating the change.