You wouldn't by any chance have a list of those 100 essential species, would you?
I wonder if there is a crater that we can fill with an inert liquid, maybe a liquid CFC, and seal off with an impermeable floating wax memiscus that is produced by life inside the "lake". If there is enough pressure and oxygen in the lake, maybe people and other animals could enter the lake and move around without space suits. If it were essentially transparent then plants could grow. Fish could be used to circulate the fluid, and disperse oxygen and other gas bubbles.
Sci-fi authors are so much better at this.