Vernal Pool Tadpole Shrimp

Vernal pool tadpole shrimp are uncommon even where vernal pool habitats occur. The vernal pool tadpole shrimp has a patchy distribution across the Central Valley of California, from Shasta County southward to northwestern Tulare County, with isolated occurrences in Alameda and Contra Costa counties. The California Natural Diversity Database currently reports 226 occurrences of vernal pool tadpole shrimp in the following 20 counties, including Alameda, Butte, Colusa, Contra Costa, Fresno, Glenn, Kings, Merced, Placer, Sacramento, San Benito, San Joaquin, Shasta, Solano, Stanislaus, Sutter, Tehama, Tulare, Yolo and Yuba counties. 

Sacramento County represents important habitat for the vernal pool tadpole shrimp by providing large, nearly contiguous areas of relatively undisturbed, high-quality vernal pool habitat. The county contains 28%, the greatest amount, of the known occurrences.

The species’ range today is much smaller than its historical distribution due to degradation and fragmentation of vernal pool habitat.  

Female vernal pool tadpole shrimp produce up to six clutches of eggs containing 32 to 61 eggs per clutch each wet season. They carry fertilized eggs in a sac on the underside of their body. The eggs are either dropped to the pool bottom or remain in the brood sac until the mother dies and sinks to the bottom of the pool. 

When the pool dries out, so do the eggs. Resting tadpole shrimp eggs are known as cysts. Cysts may remain viable for multiple years due to their protective coverings that help them withstand extreme environmental conditions and even digestion by predators. The cysts remain in the dry pool bed until hatching begins in response to rains and the return of water in the vernal pools.

The life span of the vernal pool tadpole shrimp is about 144 days on average. Vernal pool tadpole shrimp can be found in vernal pools starting in November most years and complete their entire life cycle by early May. On average, vernal pool tadpole shrimp take 38 days to mature after hatching and 51 days to reproduce. Multiple cohorts of eggs may hatch in a single vernal pool throughout the wet season given the right conditions. Vernal pool tadpole shrimp disappear before the vernal pools dry. 

Vernal pool tadpole shrimp are non-migratory and have little ability to disperse on their own. Aquatic birds are the most likely agents of dispersal of vernal pool tadpole shrimp. Large mammals are also known to act as distributors by wallowing in dirt, getting cysts caught in their fur and transporting the cysts to another wallow. Additionally, cysts can be ingested, passed through the digestive tract and then deposited in new habitats when the animal urinates.

The vernal pool tadpole shrimp is a small, freshwater crustacean that is found in vernal pools in California. They have a hard shell that is large, flattened and arched like a shield over its back. This structure structure
Something temporarily or permanently constructed, built, or placed; and constructed of natural or manufactured parts including, but not limited to, a building, shed, cabin, porch, bridge, walkway, stair steps, sign, landing, platform, dock, rack, fence, telecommunication device, antennae, fish cleaning table, satellite dish/mount, or well head.

Learn more about structure gives the tadpole shrimp its unique, tadpole-like appearance, which easily distinguishes it from the fairy shrimp. Vernal pool tadpole shrimp have 30 to 35 pairs of swimming legs that also function as gills. They have a segmented abdomen, two tail-like appendages and fused eyes.

Measurements
Length: 0.6 to 3.3 in (15 to 86 mm)
 

Vernal pool tadpole shrimp are opportunistic filter feeders. They eat small plants, waste from other vernal pool species and aquatic invertebrates, including fairy shrimp. They face competition from fairy shrimp species.