I just came across EcoSphere Closed Ecosystems, and can’t wait to get one.
As a long-time marine reef-keeper, I have a special spot in my heart for contained marine ecosystems, and just can’t get over how cool these are, especially with the minimal maintenance involved.
Basically it’s a blown glass sphere (they also have teardrop and ‘pod’ shapes) with filtered sea water, a sea fan, some decorative shells and gravel, and some cool looking shrimp who provide the main attraction as they eat the algae and breathe the air in the water. In return, the bacteria processes the shrimp poop into nutrients for the algae, which produces food and oxygen for the shrimp. A perfect circle of life!
If you follow the instructions for care (simply a room with indirect sunlight and the correct temperature) an ecosphere will normally last for 2-3 years. According to their website, some have lasted as long as 10 years and are still going.