Writen by:
Gabriel Giubellino.
ggiubellino@clarin.com

Food chain in the seas of the South

The population of krill -a small crustacean that is the preferred food of whales, penguins, seals and sea birds- has dropped by 80% since the nineteen seventies on the Antarctic Continent. Now, according to a scientific study by the British Antarctic Survey (BAS), this special category of fauna "could be endangered".

The BAS study was published in the British scientific journal Nature. Data collected in the Antarctic by nine countries over forty summers during the 1926-1939 and 1976-2003 periods, were compared. The likely cause of this reduction would be the drop in total ice volume, probably caused by global warming.

Most krill colonies are concentrated in the Antarctic Peninsula that reaches up towards the South American Continent. This is precisely one of the areas of the planet where the temperature has changed the most. "That peninsula is one of the areas of the planet where average temperature has increased most: over 2 degrees Celsius. What has varied most is not the maximum, but the minimum temperature, which is what influences the forming of ice," as explained yesterday to Clarinby Irene Schloss, a Doctor in Biology Science and a researcher at Conicet and at the Argentine Antarctic Institute.

Doctor Gustavo Gonzalez Bonorino, the Director of the Southern Center for Scientific Research (Cadic), is not able to explain with due "scientific rigor" why this should be happening on this particular peninsula. "One can only speculate that this is due to the influence of the warmer ocean current that touches the tip of the Antarctic Peninsula, and has now changed course to follow the coast of the Antarctic Continent." However, it is a fact that this drop in ice formation has not been observed on every part of the continent.

What is the relationship between ice and krill? This is explained in Ushuaia by Gustavo Lovrich, a biologist and a Conicet researcher in Cadic: "The sea ice acts as a reservoir of algae, of the algae that proliferate in spring, and are eaten by the krill."

On the BAS website (www.antarctica.ac.uk) one can read that krill (euphausia superba) is a Norwegian word meaning "food for whales". Its very name clearly identifies krill's importance in the food chain. This creature may reach six centimeters in length and live as long as five years, forming swarms of such density that up to 10,000 individuals may be found per cubic meter.

"The krill feeds on the marine algae that accumulate on the newly-formed ice -explains Lovrich-. As it is forming, the ice traps the algae. Some die, and some survive in the saline channels in the ice. During winter, when there is no light, one of the ways the krill feeds is by scraping the ice in search of food. In spring, there is an explosive proliferation of algae that invade the sea from the ice. If this dynamic disappears, so will the krill."

The study has observed that together with the decline in krill, there has been an increase of the gelatinous gilthead or salpa fish. "These are very primitive organisms, and apparently practically inedible for the fauna that feed on the krill," says Doctor Schloss.

According to this hypothesis, the krill and salpa would alternate according to the amount of ice produced. If there are few krill, the salpas will find more food -they both eat phyto-plankton- and their population will increase accordingly. At this moment, Conicet scholarship holder Veronica Fuentes is studying this alternation of fauna at the Jubany base on 25 de Mayo Island.

However, in the animal kingdom, things do not usually behave in a linear way. Although it might seem obvious that if krill tended to disappear it would cause a disaster in its wake, dragging along with it all the whales -blue, right, humped-back, Minke, Sei-, the crab-eating seal and the Adele and masked penguins, as Lovrich says: "Animals are able to change strategy and adapt." Hypothesizing, Schloss considers that under emergency circumstances some species may start eating the salpas. Angus Atkinson, the main researcher in the BAS study, demanded "urgent" further research to predict possible changes.