Estuaries are dynamic environments where rivers flow into the ocean, creating a salinity gradient that forms unique ecosystems that vary significantly over time and space. These systems serve as crucial transitional habitats, providing spawning and nursery grounds, key trophic resources, and migration corridors for many species. However, this dynamism makes estuaries uniquely vulnerable to the effects of climate change as environmental shifts and anthropogenic actions in both the marine and freshwater bookends can subsequently affect estuarine populations. UC Berkeley sits on the shores of the San Francisco Bay, one of the largest and most ecologically significant estuaries in North America. As such, our group has developed a research portfolio to study the complex interactions between abiotic drivers and community dynamics within the Bay-Delta to better inform conservation, restoration, and management activities.
The San Francisco Bay faces a number of anthropogenic threats, including pollution, water diversion, and habitat alteration. As a result, the need to reverse environmental degradation and restore critical habitats has become increasingly urgent to protect biodiversity. Construction and rehabilitation of tidal marsh wetlands are a major example of restoration occurring in the Bay-Delta. However, the ultimate effects of these restorations on community return trajectories are poorly understood. Our group is evaluating the effects that restoration activities in San Francisco Bay might have on tidal marsh food webs by comparing restored marshes to reference habitat. [Results]
Longfin Smelt are native to the San Francisco Bay and were once one of the most abundant pelagic fish species in the Bay-Delta. However, like their endangered cousin the Delta Smelt, recent population trends have shown precipitous declines. Though the ultimate causes of these declines are debated, commonly described linear relationships between environmental variables and population performance might be insufficient to describe and predict trends. As such, we have sought to explore the time-varying relationships between potential climatic drivers and Longfin Smelt populations. [Results]
Phenological shifts–or a change in timing of events within an organism’s life cycle–are one of the most commonly observed responses to global climate change. Phenological change in estuarine communities is particularly consequential as interacting species might only have limited temporal overlap. If phenological shifts push species outside of key interaction windows, trophic mismatches might destabilize food webs. Our group has undertaken work to identify and categorize phenological patterns in major estuarine systems, as well identify key periods within the year where populations might experience high risks of trophic mismatches. We found that phenological shifts were widespread in major US estuaries, but few organisms tracked long-term environmental trends. Additionally, we found that many predators are shifting asynchronously with their prey assemblages, setting up the potential for trophic mismatches in food webs across the estuary. We also found that the risk of population declines during key phenological windows was often different between predators and prey–and that these divergences might be exacerbated in the future. Our group’s research highlights the growing problem of climate-driven phenological shifts. However, there is still substantial work needed to assess the mechanisms driving phenological shifts as well as the limits of organisms to shift their phenology in response to changing climates.
Figure: Detailed examination of phenological shifts across relevant taxa of the San Francisco Bay. Local food webs are depicted along the salinity gradient—the Delta is at the low end of the salinity gradient while San Pablo Bay is at the high end. A) Distribution of the calendar day of peak abundance for taxa in each regional food web. B) Individual points represent the maximum likelihood estimate for the slope and associated 95% confidence intervals. Points and CI’s to the left of zero are advancing their phenologies, while points and CI’s to the right of the zero are delaying their phenologies (color coded by trophic level, see legend). Point size represents relative mean abundance within the relevant trophic level.
Figure: Mean critical decline risk of fish predators during their high-abundance windows paired with the potential suite of zooplankton prey within that same window. Points represent probabilities calculated from maximum likelihood parameter estimates. Lower bound represents “best case scenario” wherein decline risks are calculated with the most positive population trend and lowest amount of process error variance. Upper bound represents “worst case scenario” calculated with the most negative population trend and highest amount of process error variance. Fishes are shown in solid lines while their zooplankton prey assemblages are represented by dashed lines.