IMS Faculty Candidate Seminar: Rebecca Asch

UNC’s Institute of Marine Sciences presents a seminar by Rebecca Asch, Ph.D.. This event is scheduled for Monday, March 25th, at 2:00 pm in room 222 at the Institute of Marine Sciences. This seminar will also be broadcast live to both room 3204 on the 3rd floor of Venable/Murray Hall at the University of North Carolina at Chapel Hill and online via Zoom (Meeting ID: 252-726-6841).

Presenter Affiliation: East Carolina University

Title:  The Shifting Seasonality of the Sea: Will Climate Change Lead to Mismatches between the Seasonal Cycle of Fish Reproduction and Plankton Blooms?

Abstract: Phenology refers to the study of seasonal, biological cycles and how they are influenced by weather and climate. In many ecosystems, warming temperatures are causing phenological events to occur earlier in the year. However, temperature sensitivity varies across organisms, such that seasonal events that previously occurred synchronously could become decoupled under climate change. Many fishes time reproduction to coincide with peaks in the planktonic prey of fish larvae. Greater asynchrony between plankton blooms and fish reproduction could reduce recruitment to fisheries and result in declining catches. This seminar will investigate present-day and historical changes in fish and plankton phenology, highlighting case studies from the California Current and coastal North Carolina, as well as presenting future projections of changes from an earth system model. At the outset of this research, both the California Current and coastal North Carolina seemed unlikely locations for observing large phenological changes since they either have not experienced large climatic changes or are subject to natural, decadal climate oscillations. Nevertheless, I found widespread changes in fish reproductive phenology at the community level across 54 species. In the southern California Current, shifts in zooplankton phenology were not observed synchronously with fishes, suggesting that larval fishes may be subject to more frequent mismatches with their prey in a warming world. A model developed by the NOAA Geophysical Fluid Dynamics Laboratory was then used to make the first projections of future seasonal mismatches between phytoplankton blooms and fish reproduction under a high-emissions climate change scenario. Blooms at mid-to-high latitudes were projected to occur on average 16.5 days earlier by the end of the 21st century. For fishes whose spawning grounds are delineated by fixed geographic features (e.g., estuaries, reefs), shifts in phenology occurred twice as fast as phytoplankton. This resulted in fishes spawning before the start of the bloom across >85% of the study region. Seasonal mismatches between fishes and phytoplankton were less widespread in simulations where fishes altered their spawning location in response to changing temperatures. These results indicate that range shifts may increase the resiliency of fishes to climate change impacts associated with phenological mismatches. Lastly, this seminar concludes with a case study on the endangered Nassau grouper, highlighting why knowledge of life history is essential for projections of how marine resources will respond to climate change.