Vernal pool fairy shrimp are one-inch-long relatives of lobsters and crabs. Like lobsters or crabs, these shrimp are a type of invertebrate called a crustacean. The tiny, translucent crustaceans have 11 pairs of appendages, which they use for swimming, breathing, and feeding.
The shrimp's habitat is limited to vernal pools in Oregon and California. Occasionally these tiny crustaceans will be found in habitats other than vernal pools, such as artificial pools created by roadside ditches. They can be found in densities of as many as 200 shrimp per liter of water.
Vernal pool fairy shrimp swim around upside down, eating algae and plankton growing in the vernal pool. In order to digest their food, they must produce a thick, glue-like substance to mix with their meal. They use their legs to filter feed or scrape food from hard substrates.
This fairy shrimp is one of many species specialized for a short life cycle in seasonal ponds called vernal pools. Each winter, during the rainy season, dry depressions fill up with water and the fairy shrimp hatch. They grow to maturity over several weeks, eating algae and plankton. Before the vernal pool dries up again, the females produce hardy resting eggs, called cysts, which survive the dry season and hatch when the rains come again. This strategy allows them to avoid predators that can’t survive in such a temporary habitat.
It takes 41 days for a shrimp to reach maturity, after which point it must reproduce before dying at the end of the rainy season. Typically the young hatch in December and live until May, unless temperatures become too warm.
The vernal pool fairy shrimp is federally listed as threatened. Habitat destruction and alteration are the biggest causes of decline, but a recovery plan for vernal pool ecosystems has been put in place California and southern Oregon.
Fairy shrimp are an important food source for waterfowl—but wildlife that eat or trample the eggs are actually beneficial to the fairy shrimp. The eggs are hardy enough that they can withstand the harsh treatment and remain viable until they are deposited in a new location.
Endangered Species Project, California Department of Pesticide Regulation
Oregon Fish and Wildlife Office
Species Accounts, East Contra Costa County
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