Giant mutant carp are, alas, not an easy answer to pond-choking milfoil (as Science Cafe learned)

Excellent Science Cafe last night about invasive species. I thought I knew all about the subject, which I have written about many times, but I learned plenty. Notable were two tales of how biocontrol can go wrong. Here's the first - I need to nail down details of the second, so it will come later:

Variable milfoil, as I'm sure you know, is an invasive weed that can rapidly turn ponds into green goop. Everybody in New Hampshire is fighting it.

One idea is to put triploid carp, which can't reproduce because their eggs have been zapped, into the water body so they'll eat it all. Sounds great! But Jeff Schloss of UNH, an aquatic specialist and one of four panelists last night, pointed out a problem: The carp don't really like milfoil all that much.

As a result, they only eat milfoil after they've eaten everything else - which means that the only way they can clear milfoil from a lake is to complete denude it of all vegetation. Schloss talked about ponds that have turned into empty mudholes because the carp wiped out everything in them. Plus, he said, these "sterilized" fish sometimes manage to reproduce, creating a new invasive species problem, which makes him cautious (to say the least) about using them as a milfoil solution.

Schloss also pointed out something else: The milfoil in New Hampshire (variable milfoil) is native to southern states of the U.S. and is different than the invasive milfoil in much of the rest of the country (Eurasian milfoil). Irony of ironies, variable milfoil is endangered in Ohio! We're trying to kill it, they're trying to save it!

Schloss said side-by-side tests have shown that the variable milfoil from NH seems hardier than the same species from elsewhere in the country. In a weird way, that made us all feel proud.