University of California Water Resources Center

Vernal pools are ephemeral wetlands, typically with a diverse and highly adapted flora and fauna. We conducted the first nematode survey on record for this ecologically important habitat. Soil samples were collected on six dates from four locations in and around each of two vernal pool basins in the Santa Rosa Plateau Ecological Reserve. Nematodes from plant roots and debris were extracted in a mist chamber separately from the rest of the soil, which was sieved. An estimated fifty-two nematode genera were isolated, including at least sixty-three species. Soils from the two pools were substantially different in the composition and dynamics of their nematode communities. Nematode abundances were analyzed using the nonparametric Friedman test. Significant differences are observed between/among exact locations, sample dates and extracted sample fractions. Differences in abundance patterns are also significant across nematode genera. Simple feeding experiments were conducted to test whether some vernal pool nematodes might feed on the cysts of fairy shrimp, and thereby potentially limit the recovery of some endangered fairy shrimp species. Our observations do not suggest that this is the case. During the dry summer phase, roots and plant debris appear to play an important role in both pools as refuges for nematodes, and by extension of microscopic organisms in general. Adults of large nematodes, in genera such as Dorylaimus and Labronemella congregate preferentially in dead plant material, perhaps not only in response to drought but also because of the fine texture of the underlying soil. “Aquatic” genera such as Tobrilus persist throughout the dry phase, especially in plant debris. We recommend that management of vernal pools takes care to avoid controlled burns or other forms of removal of dead plant material in dry vernal pool beds. Future surveys of nematodes and other microscopic organisms in this type of alternately inundated and desiccated habitat should include methods for extraction of roots and plant debris.