Talk to someone who owns a tropical aquarium some time. You have to baby those things like you wouldn't imagine; it costs over 100$ a month just to keep a small home tropical aquarium alive. The initial investment is quite large too, because you need all sorts of monitoring equipment and precise lighting conditions. The bulbs my mother has to buy cost 40$ each.
We're just talking about *keeping them alive*. Let alone actually having them breed.
Freshwater aquariums, by comparison, will take whatever you can throw at them. Tropical ecosystems are incredibly delicate.
Why? There are many reasons, such as how they're adapted to a relatively unchanging environment, and as a consequence, have grown reliant on this in terms of osmosis, feeding cycles, etc. However, even more important is the issue of light: corals, anenomes, etc, are reliant not only on animal material, but even more importantly light. Not just any light, but the right kind of unfiltered intense light. Inside them, they host specialized zooxanthelae algae; with 30 days of cloudcover, even if the creatures themselves were lucky enough to survive, the algae would die, dooming the host.
Your concept of corals just going to "seed" would kill everything else on the reef. Even anenomefish - probably one of the easiest types of tropical fish to breed and keep alive - don't stand a chance without a fully established reef environment.
"Illuminant light,
illuminate me."
[This message has been edited by Rei, 01-02-2004]