I really hate this kind of brainless driveby pessimism. Look up the steel frames they're using; they're tiny. The amount of steel being added to the ocean by this project is absolutely inconsequential compared to the steel added by innumerable other human activities. Even shipping containers falling off ships dwarfs this project, let alone ships themselves sinking. Furthermore, we have decades of experience that tells us that corals and fish quite like steel shipwrecks, debris, etc. What's more, the frames they're using demonstrably do work as scaffolding for coral growth; it's not an untested idea.