Adult krill populations have dropped by 80 to 90 percent since the 1970s. There is an ongoing scientific debate about what is causing the drop, from changes in the environment to an increase in whale populations, said Andrea Piñones, a marine scientist at Center for Advance Studies in Arid Zones (Centro de Estudios Avanzados en Zonas Aridas) – Coquimbo, Chile, and lead author of the new study published online in Geophysical Research Letters, a journal of the American Geophysical Union.

Understanding the effects of climate change on krill could help scientists understand what might be in store for the entire Antarctic marine food web, Piñones said.

“The idea is to give scientists a projection of how krill are going to do under these high (carbon dioxide) emissions scenarios,” she said.

Most Antarctic krill live in an area that spans from the Weddell Sea to the waters around the Antarctic Peninsula. They start their lives in the summertime when females lay eggs near the surface. As the eggs develop, they slowly sink to depths of 700 to 1,000 meters (2,300 to 3,300 feet) – the realm of the Circumpolar Deep Water current, a mass of deep water slightly warmer than Antarctic surface waters. At this depth, the water is a cozy 2 degrees Celsius (35.6 degrees Fahrenheit), about 1 degree Celsius (1.8 degree Fahrenheit) warmer than the water at the surface. This is the ideal temperature for krill egg development. After the eggs hatch, the krill larvae swim up to the ocean surface to feed. If they cannot find food, the larvae will starve after about 10 days.

Climate models predict that as the oceans take in more heat from the greenhouse effect, the waters of the Circumpolar Deep Water will warm 1 to 1.5 degrees Celsius (1.8 to 2.7 degrees Fahrenheit) by the end of the century.

“Higher than 2 degrees Celsius and they won’t develop,” she said. “There are physiological limits.”

If the larvae make it past that first 10-day hurdle at the surface, they face a second challenge in the late summer and early fall when they need to fatten up make it through the winter. The last hurdle is their first winter, when juvenile krill depend on the sea ice algae for food, and crevices in the ice for shelter through the winter.

Climate models predict a 90-day delay in the formation of winter sea ice by the end of the century, Piñones said. Less winter sea ice means less food and shelter available for krill juveniles, which means fewer young krill will survive to adulthood and spawn the next summer, she said.

The warmer waters and lack of sea ice could lead krill habitat to shrink by as much as 80 percent by 2100, according to the new study. At that point, only localized regions along the western Weddell Sea, isolated areas of the Indian Antarctic sector and the Amundsen/Bellingshausen Sea will support successful spawning habitats for krill, according to the new study. The loss of krill habitat could cause krill populations to decline, although the new research did not quantify the drop in krill, Piñones said.

“Just about everything you can think of in the Antarctic depends on Antarctic krill,” confirmed biological oceanographer Kendra Daly of the University of South Florida in Tampa, who was not involved with the new study.