My EcoSphere, part 2 of 2

Yesterday, I introduced you to a fascinating showpiece called the EcoSphere which is a complete, working ecosystem holding some shrimp and algae and all it needs is light to run. I worked it into Rome's Evolution as part of the explanation as to why there was so little variety in the lifeforms there. Here is the second part:

     Rei stooped down to where the water lapped up against the bank and scooped up a handful of water into his mouth. Rome did the same. Rei leaned back on his haunches then extended backwards so that he was lying on his back. He looked up at the canopy above them. Nothing on this planet was as it seemed. Rome decided to lie down as well and snuggled up next to him.
     “Look,” she said, pointing to the tree tops. The trees here were of the bushier kind that Rome had discovered lining the Great Southern Bay. “The bushier cane-trees must need more water. They are aligned here along this creek. I had noticed that the ones MINIMCOM transplanted to my campus were not thriving as well. That must be why. I’ll tell him to make sure they get more water when we get back.”
     “Whatever,” Rei said. He considered their circumstances. “You know, I used to think there was something wrong with this world. Its utter lack of biological diversity. But from what you said, they must have known what they were doing.”
     “Yes,” Rome replied. “They have built an optimal system.”
     “I guess I shouldn’t be so surprised,” Rei said. “When I was a kid, I had this thing called a bio-sphere. It was a sealed glass globe. All it had was some water, some air, a dead wood-like plant, some algae, some rocks and a few shrimp.”
     “Wouldn’t the shrimp suffocate eventually?” Rome asked, “If it was a sealed globe?”
     “No,” Rei said. “That was the sleek thing about it. All you had to do was supply light. The algae made oxygen which the shrimp breathed. The shrimp ate the algae. Their waste was food for the plants and so on. It was perfectly balanced and I had it for a long time.”
     “This world is perfectly balanced as well,” Rome said. “I hope we don’t upset that.”
     Rei sat up. “We’ll try hard not to. But we’d better get going.” He stood up then helped Rome up.