Ecosystem impacts of the invasive rusty crayfish (Faxonius rusticus) over time

Invasive species have effects across levels of the ecological hierarchy, from genes to ecosystems, with negative consequences for biodiversity and global economies. These impacts likely vary over time and with invasion stage, though long-term studies on the effects of invasive species are rare. In my thesis, I use a unique long-term dataset (1975-2020) on the invasive rusty crayfish (Faxonius rusticus) in northern Wisconsin lakes to investigate the impacts of this invader over time. Since it was initially introduced in the 1960s, F. rusticus has reached hyper-abundance relative to native crayfishes and caused declines in fishes, macrophytes, and macroinvertebrates such as aquatic gastropods (snails). The red swamp crayfish (Procambarus clarkii) is another invasive crayfish that has caused declines of macrophytes, leading to decreases in water clarity in shallow lakes and wetlands in Asia and Europe. In my first study, I used remote-sensed estimates of Secchi disc depth and chlorophyll-a concentration to investigate if F. rusticus similarly decreases water clarity in north temperate lakes. Contrary to what I expected, I found a weak, positive relationship between F. rusticus and water clarity. If the positive association I document between F. rusticus and water clarity is real, F. rusticus may either be a positive driver of water clarity through a trophic cascade or may respond to changes in water clarity as benthic resources are either increased or decreased. In my second chapter, I used a long-term dataset (1987, 2002, 2011, and 2020) of crayfish, macrophytes, and snails in ten F. rusticus-invaded and control lakes to demonstrate that lake communities (macrophyte and snail abundance and richness) have started to recover after natural population declines of this invader. The recovery of lake communities that we document indicates that some effects of invasive species may be transient or time-dependent, but we still recommend managing and preventing the spread of invaders due to their severe impacts at the peak of invasion. I also report a delayed recovery of snails relative to macrophytes, suggesting that the recovery of some species after invader declines may lag behind the habitat on which they depend. Overall, my thesis provides a unique, long-term perspective on the impacts of F. rusticus, while demonstrating that lake ecosystems may be resilient over many decades to the effects of this major freshwater invasive species.U of I OnlyAuthor requested U of Illinois access only (OA after 2yrs) in Vireo ETD syste