\u201cFor us as biologists, obviously, water quality getting better is the best thing we could possibly hear,\u201d said John Bieber, co-author of the study and a biologist at Loyola University Chicago. \u201cBut if we see that the water quality is good enough now for [scud] to be able to work their way closer to Lake Michigan, then that definitely does become a more pressing concern.\u201d<\/p>\n
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The invasive species known as Apocorophium lacustre. Credit: Robert Aguilar\/Smithsonian Environmental Research Center<\/p>\n
Scud is a general term for the small crustaceans common in aquatic environments around the world. While there are some varieties of scud native to Lake Michigan and Illinois\u2019 waterways, A. lacustre is an invasive species. From its native range on the Atlantic coast, scientists believe the species made its way up the Mississippi River and into the Illinois River by 2003<\/a>. They are worried, if it reaches Lake Michigan, it could replace vital native species at the bottom of the food chain, with cascading effects on the diets of other aquatic species\u2014all the way up the chain to salmon and other game fish.<\/p>\n A. lacustre has not yet been observed upstream of the Dresden Island Pool, the waters behind a lock and dam system that guides boats toward Chicago and Lake Michigan, approximately 100 river kilometers away. To understand why, the study authors conducted experiments to see how different water conditions changed the species\u2019 movement and behavior.<\/p>\n First, researchers tested how scud reacted in waters from the Chicago Sanitary and Ship Canal (CSSC), a waterway containing treated and untreated sewage, as well as runoff from the industrialized city. About 35 percent of A. lacustre exposed to this water did not survive, and researchers suggest in-situ scud would likely choose to stay downstream in less polluted waters, if given the chance.<\/p>\n Researchers also tested how two invasive species barriers might impact the species\u2019 spread. They simulated the CSSC\u2019s \u201celectric fence<\/a>\u201d system, which has been in operation since 2002, creating an electric field in the water to prevent larger invasive species, such as carp, from breaching Lake Michigan. However, researchers found this electric barrier caused little change in scud\u2019s behavior, except at 300 percent and 400 percent of the electric field strength currently used in the CSSC.\u00a0<\/p>\n Similarly, when researchers simulated a proposed<\/a> CO2 barrier\u2014which would increase CO2 levels in the CSSC to prevent invasive species from passing through\u2014they found impacting scud would require much higher levels of added CO2 than is currently allowed by the U.S. Environmental Protection Agency.<\/p>\n \u201cThere hasn\u2019t been a lot of work with scud,\u201d Bieber explained. \u201cThis is a first step effort to be able to understand how an amphipod, like scud, can respond.\u201d<\/p>\n While research of these organisms is still in its early days, their small size means their spread is difficult to detect and time is of the essence for learning more about them. Brandon Harris, a large river fisheries ecologist at the Illinois Natural History Survey, notes these tiny creatures can travel, relatively undetected, across large distances by hitching rides on vessel hulls or in ballast water.<\/p>\n To prevent scud and other invasive species from traveling this way, the United States and Canada have implemented a variety of regulations governing how and where trans-oceanic ships should empty their ballast water, but it\u2019s still possible for small species to slip through.<\/p>\n \u201cIt\u2019s a lot harder to see a small amphipod than it is, maybe, a fish,\u201d said Harris, who was not involved in the study. \u201cWhen they\u2019re small like that, they pose a lot more issues.\u201d<\/p>\n These issues are especially salient as the waterways around Chicago are finally getting cleaner after decades of restoration efforts. In late September, for the first time in nearly a century, the Chicago River hosted its first organized swim<\/a> after the once-toxic waters were deemed safe and clean.<\/p>\n
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