Ocean Watch
By Susan Scott
Shrimp cubes are
balanced ecosystemsA reader e-mailed me this week about the closed aquatic ecosystems currently being sold in shops and on the Internet. These sealed cubes and bowls contain shrimp, snails or fish and are designed to grace desks or countertops. My reader wonders if these small containers are capable of maintaining healthy environments.
They are. Life in these small aquariums is based on the same recycling principles that drive all life on Earth. Plants need light, carbon dioxide, water and nitrogen to make carbohydrates. During this carbo production, plants give off oxygen as a waste product.
Oxygen isn't a waste product to animals, of course, since we all require it to live. In the process of eating plants' carbs and breathing oxygen, animals release carbon dioxide, water and nitrogen as waste products.
And there's the cycle of life.
When the ins and outs of plants and animals balance, the only thing you need to add to their ecosystem is light. And that's how these glass ecosystems work. You set them in a lighted place, either natural or electric, and let the plants and animals take care of themselves.
We humans are having a hard time maintaining the right eco-balance on Earth, and in a small jar there's far less margin for error. Failure can mean puny, half-starved fish or, at the other extreme, a bowl of slimy algae.
Some animals, however, are champs in these systems because they evolved to survive in tight conditions. Among these adaptable creatures are Hawaii's native anchialine shrimp, or opaeula.
The term anchialine comes from a Greek word meaning near the sea and describes coastal ponds near young lava fields. These ponds have no surface connection to the ocean, but stay fresh through a mixture of fresh and salt water seeping in and out of lava cracks.
During volcanic eruptions and other pond-altering events, such as the introduction of alien species, the red, half-inch-long anchialine shrimp hide in underground cracks. When conditions improve, even years later, the shrimp emerge and reproduce like crazy.
For Christmas this year, Santa brought me a jar of eight anchialine shrimp. These super shrimp are my second batch of eight. The first I kept in a jelly jar on my desk for more than five years. About one shrimp died per year, and when I got down to two, I set them free where I found them, in a pond on the Kona coast of the Big Island.
Five years is not particularly long-lived for anchialine shrimp. Some have lived in captivity for 20 years.
Opaeula eat the algae and bacteria that grow on the surfaces of their habitats. They also eat the shed exoskeletons of their own molts, and when their jar or pond mates die, they eat them, too.
One Hawaii species of anchialine shrimp also lives in the Maldives and in Egypt. This odd distribution of identical animals suggests that these shrimp once inhabited anchialine ponds all over the world. Some evolved into marine or freshwater shrimp, and others did not evolve at all. If you have one of these aquatic ecosystems, remember that controlling the amount of light is the way to control the inside environment and, therefore, the health of your animals.
Also remember that if you buy, collect or receive anchialine shrimp as a gift, you may have pets on your desk for a long, long time.
Marine science writer Susan Scott can be reached at http://www.susanscott.net.
