The Connecticut Department of Energy and Environmental Protection and Connecticut Sea Grant announced in a press release the discovery of a sub-adult Chinese mitten crab in a fishway in the Mianus River in Greenwich, Conn.
This unpleasant little feller is well established in European waters and is certainly moving around in ballast water, but it has also become established in estuaries on both the U.S. east and west coasts and so probably is also spreading the old-fashioned way. It has been found for several years in the Hudson River and so a spread into western CT wouldn’t be completely surprising.
[ed. note: another crab, an adult female, appears to have been found in autumn 2014. Jim Carlton, of the Williams-Mystic marine program, noted that western Connecticut would be in the “larvae shadow” of the infestation in the Hudson so periodic finds and eventual population would be expected.]