LB 20-180 - Examining phenological shifts and potential for trophic mismatches across multiple estuaries

Climate change is shifting the timing of key life-history events of species (e.g., growth, emergence, migration) particularly in aquatic ecosystems dominated by ectotherms. In some cases, these phenological shifts might lead to trophic mismatches if the timing of peak abundance between predators and prey becomes asynchronous. In estuaries, fluctuations in temperature and salinity often control population dynamics of phytoplankton, zooplankton, and fishes; thus, directional climate change has the potential to disrupt phenologies across trophic levels–potentially disrupting whole food webs. Here, we analyzed >2000 monthly time series of phytoplankton, zooplankton, and fishes in addition to two key environmental variables (salinity, temperature) over 10-40 years for the Chesapeake, Massachusetts, and San Francisco Bay Estuaries. We fitted trivariate mixed-effects meta regression models to estimate linear relationships between phenology, climate, and time–allowing for comparisons of phenological patterns within and across systems with varied climatic contexts. Accordingly, we observed phenological shifts in 27% of the taxa, but the magnitudes and even directions of change varied across taxa and trophic levels. For instance, San Francisco Bay fishes with shifting phenologies tended to delay their peak to later in the year, while many potential zooplankton prey peaked earlier. We also found that the proportions of shifting species, and the role of climate in influencing those shifts, varies across estuaries. A majority of the shifts in the San Francisco Bay are driven by changing temperature trends (56%); however, temperature only influenced 45% of shifts in Massachusetts Bay and 36% of shifts in the Chesapeake Bay respectively. Conversely, 22% of the shifts in the Chesapeake Bay, 20% in Massachusetts bay, and 15% in the San Francisco Estuary tracked salinity trends. Our results highlight that global climate change may manifest in different ways across major U.S. estuaries, and taxa may differ in their phenological responses to these climatic trends. As such, broad-scale comparative examinations that leverage long-term population monitoring data could help identify and anticipate phenological disruptions to estuarine food webs that face changing climates.