Brian F. Lantry Brent Boscarino Kelly Bowen Jocelyn Gerlofsma Ted Schaner Richard Back Jennifer Questel A. Garry Smythe Roberta Cap Michael Goehle Bryan Young Marc A. Chalupnicki James H. Johnson James E. McKenna Maureen G. Walsh 2010 <i>Hemimysis anomala</i>, a Ponto-Caspian littoral mysid, is an emerging Great Lakes invader that was discovered in Lakes Michigan and Ontario in 2006. Similar to the native mysid <i>Mysis diluviana</i>, <i>Hemimysis</i> exhibits a diel vertical migration pattern but generally inhabits shallower and warmer waters than <i>M. diluviana</i>. Because basic information on the distribution, habitat use, and biology of <i>Hemimysis</i> in the Great Lakes is scarce, the potential for food web disruption by <i>Hemimysis</i> cannot easily be predicted. Preliminary observations indicate widespread invasion of <i>Hemimysis</i> in Lake Ontario. In this study, we confirm the presence of <i>Hemimysis</i> at sites spanning the northern and southern shores of Lake Ontario and the presence of the individuals during winter months. In one horizontal tow in November 2007, over 26,000 individuals were collected with a length range of 4.4 to 9.0. mm and an average caloric density of 611. cal/g wet weight. The most effective methods for sampling <i>Hemimysis</i> were horizontal tows with either a zooplankton net in the water column or a benthic sled near the lake bottom. Although more quantitative data on the life history and distribution of this species is necessary, our preliminary observations support the prediction that the potential for <i>Hemimysis</i> to impact the nearshore food web in Lake Ontario appears high. application/pdf 10.1016/j.jglr.2010.04.012 en Elsevier Early observations on an emerging Great Lakes invader <i>Hemimysis anomala</i> in Lake Ontario article