Vernal pools are small, shallow, seasonal pools that only occur under very specific conditions in Mediterranean climate regions. Typically ranging in size from less than 100 to more than 10,000 square feet, and generally less than 15 inches deep, they form where surface depressions are underlain by an impermeable surface that prevents rainwater from percolating into the ground, resulting in seasonal ponds that flood with winter precipitation but dry completely in the summer. They harbor a diverse and unique suite of plants and animals that are adapted to these punctuated, low nutrient hydrologic conditions. Because of this, vernal pools are some of the most ecologically important and distinctive habitats in California. Vernal pools are threatened by agriculture and development, and it is estimated that over 90% of the vernal pools in California have vanished, largely due to human activities. As part of the NCOS restoration, we are helping to reverse that trend with the creation of nine new vernal pools in the southwest portion of the site (Figure 1).
Figure 1. North Campus Open Space showing the vernal pool depressions: aerial photo by Bill Dewey (left) and map with vernal pools in tourqoise (right). Note: In the aerial photo south is up, the reverse of the map.
Many of the species in vernal pools have specific adaptations for surviving in the harsh conditions of this special habitat. Coyote thistle (Eryngium vaseyi), a plant endemic to California vernal pools, has different growth forms that coincide with the different vernal pool phases (see Figure 2 for an example of a vernal pool in different phases). In the winter “wet phase”, when the pool is flooded, coyote thistle sends up long, tubular leaves like straws that reach toward the surface for oxygen collection (Figure 3). As the pool dries in the spring, the leaves open and flatten and spikey inflorescences (flower heads) form during the “flower phase”, while during the summer “dry phase”, the inflorescence sets seed and becomes a mass of painful spines that are resistant to herbivory (Figure 3). As an adaptation to the desiccation of the pool in the summer, the above ground vegetation dies back completely, but the roots remain alive underground to start the cycle again with the next winter’s rains. The tiny invertebrates that inhabit vernal pools survive the dry summer phase by forming desiccation resistant cysts or eggs that will hatch with the next winter’s flooding. Visit CCBER's webpage about vernal pools for more information and photos.
Figure 2. A restored vernal pool at UCSB’s Manzanita Village in the spring “flower phase” (left) and summer “dry phase” (right).
CCBER will restore the NCOS vernal pools by planting giant spike rush in the center, and native meadow barley grass along the edges. An inoculum will be spread and rolled into the soil of the pools, and will consist of seeds, cysts and eggs gathered from remnant and restored vernal pools in the area. Many vernal pools in California are colonized by the endangered fairy shrimp; however, none of this species were found in a close investigation of all the pools in and around the campus in 2011. That study did find that restored pools are able to support 11 unique vernal pool plant species, and the life cycles of many interesting invertebrates such as the clam shrimp. Since these pools support a diverse array of species such as dragonflies, a predatory insect, they do not support populations of mosquitoes. The pools will also support Pacific chorus frogs, which can complete their life cycle from egg to tadpole and into adult frogs during the approximately 100-day wet stage of the seasonal vernal pools.
Figure 3. Coyote thistle (Eryngium vaseyi) in the tubular phase (left), flowering phase (middle), and prickly seed stage (right).