ANTARCTIC Ocean & Seashore

Krill and barnacles of Antarctica...

Phylum Arthropoda

Subphylum Crustacea

Order Euphausiacea: 'Krill'

Euphausia spp.

This is the largest genus of Krill, with some 31 species.

Krill (image by Damon Ramsey)Krill washed up on Deception Island

There are five species of Euphausia recorded living in the colder southern oceans south of the sub-Antarctic convergence zone.

These krill have interesting variations on moulting. Crustaceans and other arthropods usually grow by cracking off their current exoskeleton, and then expanding and growing into the next one. They may do this for several stages, and thus the larger the animal, the older it is. Some krill can evade predation by moulting almost instantly, literally 'jumping out of their skin', leaving their predator with a mouthful of empty shells. It also appears that many kill can reverse the moulting order. During the miserable winter months in the southern ocean they may have to live for more than 200 days without food, so to help them survive they 'grow backwards' and their next moult is smaller and non-sexual. (They do the 'Benjamin Button'). But come the nutrient rich summer, the krill starts to moult back into bigger more sexual forms.

It is claimed that krill include the most abundant animals on earth. The 'Antarctic Krill', Euphausia superba, makes up an estimated weight of around 379 million tonnes, which makes it the species with the largest total biomass on the planet. In turn, this provides food for huge amounts of larger migrating animals, including whales, seals and seabirds.

Subclass Cirripedia: 'Barnacles'

Another group of crustaceans have adapted well to surviving in the southern ocean....

Family Coronulidae

'Whale Barnacles' can often be seen along the head of whales. particularly baleen whales such as Humpbacks. The barnacles have evolved to specifically live on cetaceans, derived from another older family of barnacles that lives on turtles and other animals in warmer waters. An individual whale may carry up to 460 kilograms of barnacles. Surprisingly, the relationship between cetacean and crustacean is considered commensal, with no benefit or harm to to the whale host. However, there is argument that the hitch-hikers must create considerable drag, especially when looking at the polar-to-tropics annual migration of Humpback whales. Conversely, some suggest that that an armour of barnacles helps male whales in combat. When the barnacles fall off (perhaps due to different temperatures and conditions when the whales migrate, or when the whales breach), you can see a ring pattern scar on the whales skin.

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