![\"Lovely](\"http:\/\/practiceconservation.com\/wp-content\/uploads\/2013\/05\/7747925682.jpg\")
<\/a>Lovely milfoil!<\/p><\/div>\n
What species are the worst offenders?<\/b> That\u2019s a pretty complicated question since it requires defining what a \u2018significant impact\u2019 is, as well as categorizing good and bad. Additionally, these invasive species all came from some place, so they are native flora in someone\u2019s backyard. However, there were a few names that kept coming up again and again in variety of places: Spartina alterniflora<\/i> (a type of marsh grass), Caulerpa taxifolia<\/i> (popular in aquaria), Hydrilla verticillata<\/i>, Eichhornia crassipes<\/i> (water hyacinth), Ipomoea aquatic<\/i> (Chinese water spinach), Myriophyllum spicatum<\/i> (European milfoil). Records for these species as invaders span the globe and a variety of water habitats. Some are an issue in coastal wetlands and in marine ecosystems (like Spartina<\/i> and Caulerpa<\/i>) while others are found in freshwater systems. The US<\/a>, IUCN<\/a>, other countries, and individual states have lists of invasive vegetation in case you want to see what\u2019s a real issue where you are (and what you\u2019re not supposed to be growing\u2026)- what was very interesting to me was looking through the US Federal List of Noxious Weeds and then searching the internet for vendors- some of these are unnervingly easy to find and don\u2019t mention their status as invasives (in fact, I found detailed instructions on how to take very good care of water hyacinth).<\/p>\n Exactly what is it that makes them so scary? <\/b>Well, it depends on the species, but some of them have the real capacity to modify the environments around them, and that can be a problem for native flora and fauna, as well as for humans. Water hyacinth and hydilla are on Florida\u2019s list of \u201cmost invasive\u201d plants because they tend to reduce surface water flow and dissolved oxygen in the water, so they cause more sediment to settle which can fill channels and canals, and hydrilla can outcompete native eelgrass and alter the vegetation available to native fish and invertebrates (Gordon 1998). Milfoil was found to suppress and displace native plants from deeper water in New York\u2019s Finger Lakes region (Madsen et al. 2008) and was linked to loss of habitat for larger fish in lakes in California and Nevada (Eiswerth et al. 2000). Spartina can trap sediment, changing west coast mud flats to raised marshes, and yet there are real concerns along the east coast about loss of native spartina as phragmites reeds spread. So, even the location is important to determining invader impact. And lest you think that the invasions are in one direction, in China fanwort from eastern North America is a problem (Zhang et al. 2003), and the Senegal delta in Africa has seen changes in water flow, sedimentation, and fauna with the presence of water hyacinth, water spinach, and other invasives (Fall et al. 2004). Having said all of this, there is still debate about whether invasive species are automatically bad and whether they can suitably fill ecosystem roles in their new habitat<\/i> (Capers et al. 2007; Madsen et al. 2008; Mueller & Hellmann 2008). In some areas, invasives create a monoculture which negatively impacts native flora and fauna, in others invasives improve water quality. And how do you address an invasive which may be threatened in its native range? These situations can get pretty complicated.<\/p>\n How are these aquatic invaders moving around?<\/b> We can take a lot of credit for this- we\u2019re doing a pretty good job of providing transportation. In some cases, we\u2019ve deliberately introduced nonnative species, such as the tomatoes which are now such a staple of Italian cooking (and originally from the Americas) or the chickens whose eggs I used for baking a few days ago (origin in southeast Asia) and sometimes these species get out from under our control- in the case of aquatic plants, that could be as a result of spreading aquaculture or even heavy rains which caused your pond to overflow into a nearby stream. We\u2019ve also carried species unintentionally during the course of international trade, for example in the dirt and water ballasts of ships (which is one reason to have ships discharge ballast water mid-ocean and then take on fresh water for the remainder of the journey, although it\u2019s not a complete solution), or even on planes (brown tree snake meet vulnerable Guam bird species, Guam bird species meet bad news\u2026). And then there at the introductions done intentionally but without really thinking about it<\/i>– Caulerpa and other species found in home aquaria tend to be released into the wild when people get tired of caring for pet fish and decide to liberate them- since the individuals in aquaria are more likely to be larger, mature specimens with the capacity for reproduction, versus those in ballast water, they already have a head start (Padilla & Williams 2004).<\/p>\n