The Black Sea is one of the few places that's not super super cold that's immune to them. It's because you've got like a very thin layer of oxygenated water near the surface and then below that, it's like super anoxic. So the worms just can't survive. If a ship sinks quickly enough in the Black Sea, it won't be affected by shipworms or it shouldn't unless that also changes with climate change - which is possible.