A MARINE MEGAFAUNAL EXTINCTION: CAUSES AND CONSEQUENCES

Marine megafauna are currently facing significant population declines due to anthropogenic environmental changes and impacts. Despite these threats, there is little understanding of the ecological impacts on marine community structure if megafauna were to go extinct. Using palaeontological data to model how ecosystems have changed during past extinctions of marine megafauna can provide insight into how extant systems may be altered in the future.

A marine megafaunal extinction at the end of the Pliocene (~2.5 million years ago) saw significant declines in mammals, birds, turtles and sharks, including apex predator Otodus megalodon. These patterns of extinction mimic the projected declines seen today. It is hypothesized that global sea level drop due to cooling over the Plio-Pleistocene boundary led to a decrease in neritic zone (highly productive habitat where most megafauna source their energy) area and was the primary driver for these extinctions. We investigate (1) how ecosystem structure changed following the loss of these megafauna through reconstructing metacommunity food webs before and after the extinction, and (2) the environmental pressures that led to these megafauna specific extinctions and how this varied across different geographic regions.

Despite significant losses, community structure was mostly unchanged following the extinction event indicating that marine food webs were robust against extinctions of megafauna, particularly those occupying higher trophic levels. Further, we find extinction rates were not consistent globally, exhibiting regional variation. The North Atlantic Ocean did not show a significant peak in extinction rates over the event compared to other ocean basins. This suggests that the North Atlantic was less impacted by this extinction event, perhaps due to this area having a larger extent of continental shelf which would minimise losses of neritic zone area.

Our findings highlight the stressors which can drive marine megafaunal losses and give a better understanding of how marine community structure may respond to pelagic extinctions of large-bodied taxa.