A krill at its final larval
stage.
Photo: So Kawaguchi

Researchers have found that spring-time growth of sea ice algae is critical to krill growth and reproductive potential.

This could mean that future changes in sea ice coverage could threaten the species, which plays a key role in the Southern Ocean food chain and is a source of nourishment for many whale species.

The Australian Antarctic Division measured krill populations during the annual formation and retreat of sea ice around Antarctica. Antarctic krill feed on ice algae during winter and spring, when food in the water column is scarce.

The researchers found that adult krill were just about to start boosting their maturity in preparation for summer reproduction, by utilising ice algae under ice floes as a food source, as well as phytoplankton blooms in areas where the ice had started to retreat. During the voyage krill larvae were also found to be on the verge of accelerating their growth rates, in preparation for summer.

Undoubtedly, the amount and timing of algae associated with sea ice, and in open water at retreating ice edges, are very important determinants for krill population dynamics. Preliminary analysis of the data suggests that the investigation, named the Sea Ice Physics and Ecosystem eXperiment (SIPEX) was carried out at the very moment when biological activities were taking off in the survey area off East Antarctica.

SIPEX used newly developed sampling and observing systems. These included an instrumented Remotely Operated Vehicle (ROV) equipped with a sonar, light sensors and camera system, to observe and film krill under sea ice, and a custom-built Surface and Under Ice Trawl (SUIT) and Rectangular Midwater Trawl to collect animals for physiological experiments.

The Australian Antarctic Division hope to use the results of the project along with the new sampling methods to predict what might happen to krill populations given possible future changes in sea ice coverage.