What the Heck Are Fairy Shrimp?

Most everyone knows what shrimp are, but what the heck are fairy shrimp? As with all shrimp species, fairy shrimp need water, but in the case of the fairy shrimp, they need a vernal pool or very clean and clear lake. So, what is a vernal pool? Well, as the name implies, it has something to do with green-the word vernal means green. Vernal pools are short term pools that generally appear after a rainfall. They tend to be found in a swale or depression in a meadow and have different plants than the surrounding land. These plants can stand out as being greener and being more water loving, since they will be living in the pond when water collects.

Vernal pools, however, are fleeting and will soon dry up. For this reason, organisms that rely on the pool must, out of necessity, reproduce quickly. Their life cycles are fast and in the case of the fairy shrimp, the eggs that were deposited on the floor of the pool the last time the pool was wet have to hatch very fast. In fact, the will usually hatch in about 30 hours after being wet. The baby shrimp grow by moulting, or shedding, their exoskeleton until they reach adulthood. They entire life cycle of a fairy shrimp is only a little over two weeks. This means they have to hatch, mature, mate and lay eggs in about two weeks.

The fairy shrimp are very tiny, about half an inch to one and a half inches in length. They are crustaceans that use eleven pairs of feathery legs to swim around. Once the male mates with a female, he dies within a few hours. The female will keep her fertilized eggs with her in a sack for several days before letting the sack fall to the bottom of the pool. The eggs won’t hatch during the pools current wet condition. Instead, they will stay in a sort of dormant state until the pool dries up and then becomes wet again either in the spring or fall. Fairy shrimp are found in several states, but in California, there are several different species, including the Vernal Pool Fairy Shrimp (Branchinecta lynchi) which is a federally threatened species. Most fairy shrimp are in danger of losing their habitat due to urban sprawl and off highway vehicle traffic. These tiny shrimp eat bacteria, algae and other microscopic organisms. Due to their need for the delicate vernal pools, the federal government-the US Fish and Wildlife Service-designated certains areas as critical habitat, which means those areas are protected to preserve the species that rely on it, including the fairy shrimp.