If it becomes loose in the water it would get in their gills and bottom feeders would suck it up off the sea floor and harm them the same way it harms lungs. That said, im not sure there would be loose pieces of it leaving the cement. Plus if someone REALLY wanted the properties of asbestos, there are plenty of ceramic wools that are pretty much identical products (with the same risks of asbestos) that are comparable in price and not subject to the same kind of rules. However nobody that makes ceramic wool would be dumb enough to pretend that shit isn't harmful to be exposed to.

I would wager that most marine animals would be unaffected. Mammals would hold their breath, and any other animal with gills already deals with fine-grained sediment.

Might perforate the blood vessels in the gills and enter the blood stream? Later on we eat it?