Species richness, endemism and ecology of crustacean assemblages in northern California vernal pools

Ephemeral pools occur worldwide, provide habitat for organisms with a variety of life history strategies, and may have served as evolutionary refugia for some taxa since Mesozoic times. Yet, our understanding of the ecology and evolutionary history of ephemeral pool communities is hampered by a paucity of such basic data as the species composition of pool assemblages. We surveyed 58 vernal (ephemeral spring-time) pools from 14 sites in northern California for crustaceans, and found diverse assemblages composed largely of endemic and rare species. Sixty-seven species of crustaceans were found, and as many as 30 of these may be new, undescribed species. Differences in species composition among pools correspond with physical and chemical aspects of the habitat (depth, solutes concentration, elevation, biogeographic region), and with existing geologic/floristic-based habitat descriptions. Species richness is positively correlated with both depth and surface area. This relationship can be explained in terms of hydroperiod (accommodation of species with slower developmental rates in long-lived pools, greater time for temporal resource partitioning) and size (spatial habitat heterogeneity). High species richness and numerous co-occurrences of congeneric species in temporary pools may be due to super-abundant resources, low levels of predation, and annual truncation of the community which prevents ecological interactions from going to completion. The results of this survey underscore the need for conservation of the vernal pool habitat and endemic vernal pool species in California. The best preservation strategy will include many pools at each site, multiple sites of each habitat type, and all identified habitat types.