On the show, thinking on my feet, I said that Marmorkrebs might have some competitive disadvantages because they are a small species, and size is a very important factor in crayfish competition when animals are in one-on-one interactions. (When you match individuals for size, Marmorkrebs hold their own, however).
This is a similar question to the one I fielded at the Ecological Society of America meeting a few weeks ago. One crayfish get loose in a watershed, there is not much that you can do.
In a bit of l’esprit d’escalier, I might have added in my reply to Kiki that the kryptonite of marbled crayfish might be their reliance on humans. In general, crayfish are not all that mobile. Yes, some species are comfortable with leaving the water and making a portage to a new home, but in general, they will spread from one watershed to another only fairly slowly. They are horrible once they get established, but they have a hard time getting that first toehold without humans moving them around.
Left to their own devices, Marmorkrebs never would have made it to Madagascar, or Japan, or anywhere else. In North America, Marmorkrebs are human captives. Let’s keep it that way.
