I know my solution can sound like if I want to create a new Zoo but more sophisticated, but the marine ecosystem is one that is being more affected for Climate Change due to the rise in the water temperature that means that at some point we won’t be able to eat some species of fish because they will be dead or because we won’t be able to fish them because they are moving North or going deep to find the optimal conditions to live. In my opinion it would be better to invert the money in create the environment to protect the fishes and have aliment to feed the human population than lost all of them and have to get rid of fish in our diets.
I know extinctions have occurred all over the past but is also true that in this case we are also contributing to it, the extinction in the past were only caused by natural reason but the one that could happened in some years in going to be increase by us. So because we have the resources may be we can protect those species, if they are in a place where the conditions are optimal to live they are not going to get extinct because they were able to reproduce. I am not talking of about bringing species from one environment to other because as you said in your example that could have negative consequences, although one of the solutions that scientist are proposing is to move the species that are in risk to a different place and one of the risk is that the endemic species could be affected by the new species. But that is not what I am suggesting I am suggesting to keep each specie in their own create environment and only combine those that are adjust to live together already.
The last problem that you talked about is the money, well I said in my solution that this will be a place that could be maintenance with the money from the visitors as a Zoo. If we keep species that are not visible outdoors in this “Zoo” people will come and visit, also if there is species that are use as aliment for humans the many obtained for selling those species can be used to support the “Zoo”.