Big extinctions don’t just wipe out a lot of species. They also send ecological cycles reeling for millions of years, a new study suggests.
Following massive die-offs, the natural processes that keep carbon flowing through marine ecosystems — from tiny photosynthesizers to big fish and between the bottom and the top of the ocean — get broken. For millions of years after at least two global disasters, marine communities were too unstable to keep the molecules churning, researchers report in the February issue of Geology. These “chaotic carbon episodes” could have big ramifications for extinctions in the modern era, say scientists from Brown University in Providence, R.I., and the University of Washington in Seattle.
In healthy marine ecosystems, diverse swimming predators, lazy filter feeders and myriad other organisms keep the carbon flowing nonstop, says study coauthor Jessica Whiteside, a paleobiologist at Brown. But after a global extinction, when only a few plants, animals or single-celled critters occupy each rung of the food chain, minicatastrophes like diseases or climatic shifts take big tolls, she says. “If you already have a weakened state of ecosystems, these things that would normally be minor variations now become wildly oscillating,” she says.
The team looked particularly at the diversity of ancient octopus-like animals called ammonites, which were ultimately wiped out by the same extinction that killed the dinosaurs. Ammonites often swam to catch prey as well as floated idly, snagging debris from ocean currents. But for millions of years after the end-Permian mass extinction 250 million years ago, as well as after the end-Triassic mass extinction 50 million years later, few swimming ammonites survived.