Archived DNA reveals marine heatwave-associated shifts in fish assemblages

Quantitative environmental DNA (eDNA) approaches improve our ability to characterize the impacts of marine heatwaves on marine ecosystems, revealing unprecedented novel species assemblages. Work by Pacific Marine Environmental Laboratory (PMEL), the California Cooperative Oceanic Fisheries Investigations (CalCOFI), and partners revealed marked shifts in California Current Large Marine Ecosystem fish larvae communities across a 23-year time series with large changes in response to the 2014–2016 marine heatwave. The high abundances of both Northern anchovy and southern mesopelagic (i.e., more tropical) species were unique in the previous 70 years of CalCOFI surveys, suggesting that climate-associated ecosystem shifts will be without modern analog. 

Our results demonstrate the power of eDNA metabarcoding from ethanol preserved bulk samples to unlock important insights into community dynamics over time, creating novel research opportunities from preserved sample collections.These efforts are valuable to providing higher resolution zooplankton and fish larvae data from archived NOAA sample collections like CalCOFI and Ecosystem Fisheries-Oceanography Coordinated Investigations (EcoFOCI). These higher resolution approaches may prove critical in modeling and predicting future ecosystem change, particularly difficult to study ecosystems like coastal pelagic fishes. These approaches are also widely applicable to the bulk collection of community samples including phytoplankton, insects, pollen, gut contents, and microbiomes, among many other targets. As such, the methodology we present here provides an important tool to efficiently understand modern and historical changes in ecological communities.