UC San Diego

Temporary freshwater ecosystems like vernal pools sustained by precipitation are a hotbed of diversity with unique species that have evolved life-histories to cope with the impermanence of their environments. Climate change is expected to amplify interannual variation in precipitation in many regions; therefore, future vernal pool ecosystems may face greater uncertainty in hydroperiod. The impact of elevated fluctuations in water supply on aquatic communities in temporary environments is unknown. To understand the response of invertebrate communities inhabiting ephemeral freshwater pools to variation in rainfall, we conducted a mesocosm experiment manipulating rainfall to alter the amount and variability of precipitation over 4 years.

We found that precipitation affected invertebrate abundances, but increasing variability had little effect on population densities and that past conditions are weak predictors of current population levels. The first three years of the experiment coincided with a historic drought in San Diego, CA, while the final year was the second wettest on record. Many aquatic invertebrate species that were present initially became extinct across experimental treatments during the drought, suggesting that some native species cannot survive prolonged periods of drying in small pools. Our results indicate that some vernal pool invertebrate populations are highly resilient to interannual variation in precipitation while others were unable to persist through a historic drought even when precipitation was experimentally enhanced.