Antarctic krill needs different regions to grow up. | Polarjournal
Antarctic krill (Euphausia superba)

The Antarctic krill Euphausia superba plays a key role in the Antarctic ecosystem, as most of the animal species of the Southern Polar Sea feed on it. Therefore, an understanding of its distribution and its complex life cycle is essential to deepen our findings of Antarctic ecology. Now British researchers have found that krill has to be in different regions over the course of its life for a healthy development. The Antarctic Peninsula plays an important role as a nursery. The results of the work were published this week in the journal PLOS One.

Many aspects in the life of the only 6 centimetres sized crustaceans are still not entirely clear to science. This despite the fact that Euphausia superba is one of the most investigated animals of Antarctica. This is due to a large part because of its habitat, the Southern Ocean and its difficult weather conditions. But also the fact that krill is not distributed equally everywhere plays an important role. So far, it was known that the Antarctic Peninsula region is one of the “hot spots” for krill. A team of scientists from the Plymouth Marine Laboratory PML, the British Antarctic Survey BAS, the University of Southhampton AND the UK National Oceanography Centre NOC investigated the distribution of krill in its various life stages, from larvae to adult. To this end, they collected the data of thousands of net hauls from krill fishing over the past 41 years and extracted the data on krill larvae. They combined this data with two other data sets on krill of later stages and thus created, for the first time, distribution maps of krill in all life stages.

One of the well-known hot spots for krill is the Antarctic Peninsula. Here, in their initial stage, the animals find ideal conditions such as ice, lots of phytoplankton and little food concurrence. Picture: Michael Wenger

The results of the scientists show that adult krill has a much large distribution area, whereas the spawning area only covers a small area, especially in the shallow waters of the Antarctic Peninsula. This creates a specific hot spot for krill larvae in the southern Scotia Sea. As they grow, the crustaceans continue north towards South Georgia, another known hot spot for krill. The researchers suspect that this geographical partitioning serves to avoid food competition or to avoid possible cannibalism between adult animals and larvae. Nonetheless, the results of this study clearly demonstrates the importance of the Antarctic Peninsula for krill development. However, as the Peninsula in particular is moving into the focus of the krill fishing industry due to improved fishing and storage possibilities as well as the increased decline in pack ice formation, the researchers urge for a cautious approach. To this end, Frances Perry, PhD student and lead author of the study states: “Whilst fishing areas obviously overlap with areas of high adult density, this study shows for the first time that fishing also overlaps with spawning sites. It is important to protect these sites from the potential impacts of fishing. We need to understand the dynamics of this complex ecosystem so that it continues to support the diverse and commercially important Southern Ocean food web.”

The video shows an adult specimen of Euphausia superba swimming and, in slow motion, the swimming movements with its hind legs. Food intake with the converted front legs is also shown. Video: David Cothran

Source: British Antarctic Survey / Perry et al. (2019) PLOS One 0219325

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