Ecological effects of marine extinctions: from the Pliocene to the Anthropocene

The fossil record of the marine megafauna, the largest animals in the oceans, has revealed that in the Pliocene(~3Ma), habitat loss caused the extinction of one third of their genera, along with nearly one fifth of their functional diversity. Such a level of ecological loss contrasts with the almost negligible changes after the (mass) extinction of benthic invertebrates around the same time. Unlike the marine megafauna, small invertebrates can share similar ecological traits and thus be highly redundant and ecologically resilient in the face of extinction. The much larger marine megafauna, on the other hand, tends to be functionally unique and therefore highly vulnerable. Given that the Pliocene extinction left the marine megafauna functionally depleted, how will they respond to the current extinction crisis? Forty percent of marine megafaunal species are currently threatened. Simulated extinction scenarios forecast this could result in the loss of up to half of their ecological functions. Sharks, in particular, show greater-than-expected losses of functional diversity. Biogeographic analyses further indicate that megafauna functional richness is globally greatest along the tropical continental shelf and oceanic island environments. Meanwhile, high latitudes harbour the most functionally unique species. The protection of these areas could therefore help safeguard the key ecological functions these organisms play in marine ecosystems.