I wonder what will be algae/flora impact on a heat exchange after year or two. This thing will be warm and stationary so it will became overgrown really fast.
I imagine the first step would be to use standard marine anti-foul paint on the exchangers. But that only works for a few months at best.
After that, I'm not so sure. Perhaps a slow, continuous movement of an exchange surface past a hard surface would do the trick. When this stuff is young, it's easily wiped away, but once it's there for a while you get real problems.
The heat from hydrothermal vents on its own wouldn't support ecosystems in deep water, they also feed out various useful chemicals and nutrients. The base of these foodchains is creatures that can build biological carbon stuff using chemical energy from that instead of using light, called "chemosynthesis".
