From what I've heard, the Zebra mussels have caused over $5 billion in damage so far in the Great Lakes.
As a "trailer sailor" I don't sail in lakes with Zebra/Quagga muscles, since I don't want to take the chance of spreading them when I launch in another lake. It sounds like they could be a huge problem for someone with a moored sailboat, especially if you have an inboard engine that has through-hulls for coolant water.
I think in the long term the mussels will either kill everything and sterilize the lakes they're in wiping themselves (and all other species) out, or else they will reach an equilibrium with reasonable population levels, probably wiping out other competing species in the process. Either way you're wiping out native species - possibly some which we depend on for food and income.
You never really know what will happen when you introduce an invasive species, and it can be drastically different in different areas. What played out in the great lakes might not be the same in Lake Texoma.
They're not the end of the world, but they can cause a lot of damage. I'm happy to see that they now have somewhat effective programs in place to keep them from spreading further.
Same thing you always do.
About 20 years ago Zebra muscles were found in the Great Lakes. At the time, it was predicted that the sky was falling, the fisheries would die and all hell would break loose, not too mention that several million people rely on those lakes for their drinking water.
Fast forward to today. The fisheries are doing just fine, the drinking water is just fine and the sky did not fall.
On the upside water clarity has improved and algae production seems to be less.
On the downside, the little buggers do tend to clog things up a bit.
So there will be more cleaning/replacement of intake grates and maybe a little more work cleaning up the boats.
Then again, those things almost sound like business opportunities.