Microscopic ocean creatures offer clues into our warming climate.

For hundreds of millions of years planktonic foraminifera -- single-celled, microscopic, hard-shelled organisms -- have inhabited the ocean at the bottom of the food chain. Seemingly average specks in a vast ocean, these organisms actually offer clues into the future changes in global biodiversity and a warming climate.

Anshuman Swain, postdoctoral researcher in the Department of Organismic and Evolutionary Biology and a Junior Fellow in the Harvard Society of Fellows, and co-author Adam Woodhouse, University of Bristol, used a high-resolution global dataset of planktonic foraminifera fossils, that’s among the richest biological archives available to science, to determine their use as an early warning system for future extinction of ocean life.

The study, published in Nature, shows that environmental events leading to mass extinctions are reliably preceded by subtle changes in how a biological community is composed, thus acting as an early warning signal.

Swain and Woodhouse previously published a study in Nature that examined foraminifera's fossil record and found the formation of polar ice caps drove changes in the marine plankton communities over the last 15 million years.

Using the Triton database developed by Woodhouse, the researchers learned how the composition of foraminifera communities changed over millions of years. They focused on the Early Eocene Climate Optimum, the last major period of sustained high global temperatures since the dinosaurs, analogous to worst-case global warming scenarios. They discovered that before an extinction pulse 34 million years ago, marine communities were highly specialized everywhere except in the southern high latitudes.

The finding implies that the micro-plankton migrated en masse to higher latitudes away from the tropics, and indicates that similar community-wide changes are evident in fossil records long before actual extinctions and losses in biodiversity occur.

Going forward, Swain and Woodhouse believe it's important to monitor the current structures of biological communities to better predict future extinctions. According to Swain, the study's results from the foraminifera make it possible for more investigation into other organismal groups, including other marine life and insects. These studies may even ignite a revolution in paleoinformatics, an emerging field that uses large spatiotemporally resolved databases of fossil records to find new insights into the Earth's future.

Image: Anshuman Swain with fossil specimens. Photo by Kris Snibbe/Harvard Staff Photographer