Fish production and diversity in the Paleocene-Eocene Thermal Maximum—Increased production but no novel faunas during a “Future Earth” analog

Abstract:

A partial analog for future global change is the Paleocene-Eocene Thermal Maximum—a transient episode of warming, acidification, and biogeographic change at ~55.5 Ma. The PETM is known to have triggered extinction in some deep sea biotas, extensive biogeographic range shifts, and the common occurrence of ‘excursion biotas’—non-analog occurrences of species that are typically rare in the open ocean before or after the PETM. Here we report on the impact of the PETM on fish production and biodiversity. Our data include the mass accumulation rate of fish teeth and denticles as well as an analysis of tooth morphotypes for three PETM sites: ODP 1220 and 1209 in the Pacific, and ODP 1260 in the equatorial Atlantic. Tooth morphotypes hardly change through the PETM and consist of abundant midwater species (angler fish and flashlight fish) in addition to sharks and epipelagic fish. There is no evidence for a non-analog ‘excursion biota’ during the PETM, suggesting that fish experienced fewer geographic range shifts than the calcareous and organic-walled plankton where excursion biotas are commonplace. Fish mass accumulation rates are also relatively stable before and after the PETM although all sites show a transient rise in fish production at the onset of the PETM or within the later part of the “PETM Core”. These results broadly match published estimates of PETM export production from biogenic barium fluxes. Our findings run counter to “Future Earth” models that use climate forecasts for the next century to predict the impact of global change on fish stocks. These models suggest that future warming and ocean stratification will decrease most tropical and subtropical ocean fish production, accentuate fish production in the boundary currents and generally shift production toward higher latitudes. A resolution of “Future Earth” models and PETM data may reflect the different timescales of observation and stages of ecological response to severe global change.