(S)ome environmentalists, as well as federal and independent scientists, question whether an artificial reef program provides ecological benefits. Some view the creation of artificial reefs as a dumping ground for unwanted industrial trash and claim it to be an economic shortcut opportunity for recycling. Others note that although most artificial reefs offer potential habitat for certain kinds of marine life, these are not always environmentally harmonious homes. Artificial reefs can cause damage to natural habitats during their construction and can displace naturally occurring species and habitats. Also, because they tend to concentrate fish unnaturally, they can become more vulnerable to overfishing.
read more at http://voices.nationalgeographic.com/2014/11/06/artificial-reefing-the-blue-solution-to-americas-aging-infrastructure/