[classicman]

The data suggests that initially it draws fish from other areas and over time, as the reefs take hold in the environment, the reefs increase the fish population by creating a new place for smaller organisms and species to live and breed. This works its way up the food chain to larger species and so on.
Personally, it has increased the places to fish in my area - the older spots are still productive, but there are new ones now as well. To me, that indicates increasing populations. Thats the only personal experience I can bring to the issue.