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 marine organisms, such that seasonal events that previously occurred synchronously are likely to become decoupled under climate change. In temperate, marine ecosystems, fishes often time reproduction to coincide with plankton blooms. Greater asynchrony between these events could increase larval fish mortality, reduce recruitment to fisheries, and result in declining fish catches. This seminar will investigate historical and future changes in the phenology of plankton and fish reproduction using long-term oceanographic time series and the NOAA Geophysical Fluid Dynamics Laboratory's Earth System Model (GFDL ESM2M). In the southern California Current, decadal changes in the phenology of 43 species of larval fishes were investigated between 1951-2008. 42% of the species exhibited increasingly early peaks in larval abundance. Differences in habitat use were observed between species with long-term advances in phenology and a smaller subset of fishes with delayed phenology. In the second half of the seminar, the GFDL ESM2M model will be used to project changes in the phenology of fishes and phytoplankton globally throughout the 21st century. Under a high emissions climate change scenario, phytoplankton blooms at latitudes >40° N are projected to occur on average 16.5 days earlier by the end of the 21st century. For fishes whose spawning phenology is influenced by sea surface temperature and whose spawning grounds are delineated by fixed geographic features, shifts in phenology occurred twice as fast as phytoplankton. This resulted in fishes spawning before the start of the phytoplankton bloom across >85%. Seasonal mismatches between fishes and phytoplankton were less widespread in simulations where fishes altered their spawning ground 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, buffering against potential declines in larval survival, recruitment, and fisheries.

Rebecca Asch is an Assistant Professor of Fisheries Biology at East Carolina University (ECU). She has received a B.A. in cultural anthropology from Smith College and a M.S. and Ph.D. in biological oceanography from the University of Rhode Island and Scripps Institution of Oceanography, respectively. Prior to arriving at ECU, Dr. Asch was a Postdoctoral Research Associate and Senior Nereus Fellow at Princeton University's Program in Atmospheric and Oceanic Sciences. In addition to her research on the phenology of fishes, Dr. Asch's past and current work has addressed topics as diverse as the effects of bottom fishing disturbance on benthic invertebrates, the spread of an invasive tunicate species, plastic ingestion by mesopelagic fishes, the influence of oceanic conditions on the spawning habitat of forage fishes, and climate change effects on spawning aggregations of reef fishes.

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