Lythrum salicaria?

Question

how have other organisms been affected?

Answer 1

What this plant (purple loostrife) does is out-compete other native wetland plants and replace them around wet areas.  This, in turn, impacts wetland animals which rely on the native wetland plants (cattails, grasses, sedges) for food, nesting materials, and breeding sites.

It can also physically slow the movement of water in a wetland if it grows thickly enough, and lower flow can lead to changes in the substrate (more fine materials will settle out of the water which can impact spawning habitat for fish) as well as lower amounts of dissolved oxygen in the water.