Extreme melt restructured invertebrate ecosystem in Antarctica, scientists say

In the McMurdo Dry Valleys, a warm summer in January 2002 contributed to record melt and re-arranged the composition of invertebrate communities, such as nematodes and tardigrades, or “water bears” that live there, establishing dominance among water-thriving creatures.

The findings, based on more than 30 years of collected data through the National Science Foundation’s (NSF) McMurdo Dry Valleys Long-term Ecological Research Program(MDVLTER), were published in the journal Nature Ecology and Evolution on Aug. 7. NSF manages the U.S. Antarctic Program.

“Our study shows that, while gradual warming or cooling trends certainly drive changes in an ecosystem, an extreme event can have a much more observable effect on the environment, essentially hitting the ‘re-set’ button,” said Jeb Barrett, a professor of biological sciences in the College of Science and Global Change Center affiliate.  “The effects of that warm month 15 years ago can still be seen today.”

The McMurdo Dry Valleys is a Delaware-sized polar desert that makes up approximately 2 percent of the Antarctic continent. It is comprised of soils, glaciers, melt-water streams, and ice-covered lakes.  Due to harsh conditions, it is home only to microorganisms, mosses, lichens, and a few species of invertebrates, which researchers study to better understand the limits of life.  The area has also been used to test space vehicles intended for Mars, due to the planet’s comparable conditions.

Prior to the 2002 melt event, scientists had observed a cooling pattern in the region, said Barrett.  At that time, the cooling temperature resulted in decreased metabolic activity and reproduction among invertebrates. The trend was inconsistent with warming in other regions across the world, Barrett said, and may have been associated with ozone loss in the Antarctic.

But in 2002, the unforeseen warmth caused glaciers and ice to melt, resulting in gushing streams and lake levels to rise more than two meters in two weeks. Invertebrate species responded differently to the event, with some benefitting and others not.

“It is hard to predict these types of events, and they can change an ecosystem forever,” Barrett said.

“This flood year was the pivot point,” said Michael Gooseff, a fellow in the University of Colorado Boulder’s Institute of Arctic and Alpine Research (INSTAAR) and the lead investigator for the MDV LTER project. “Prior to that, all physical and biological indicators had been moving in the same direction.”

Established in 1993, the goal of the MDV LTER project is to better understand the unique dry valley ecosystem structure and function. Barrett has been part of the program since 1997.

“The natural world operates in nonlinear ways and on many different time scales, from daily cycles to processes that take centuries,” said Paul Cutler, the NSF program officer for the project. “The LTERs are instrumental in measuring and deciphering these complexities in order to inform basic understanding of ecosystem functioning and to refine predictions of the future of critical ecosystems, particularly in areas like the Dry Valleys, which maintain an ancient, but potentially delicate ecological balance.”

A MDV LTER project funded by NSF this year will test the hypothesis that increased hydrological connections will result from enhanced melt conditions, as observed in the 2002 flood event. This enhanced connectivity is expected to amplify exchange of biota, energy, and matter across these polar desert landscapes, resulting in a homogenizing of ecosystem structure and functioning in the McMurdo Dry Valleys.