Ecology & Invertebrates
ANTARCTIC Ocean & Seashore

Water & Ice

Water has some unusual features which have major effects on the environment of Antartica. One of the (many) weird things about water is that, while most elements and compounds are denser when they are solid, water is at is densest when it is liquid. The density of sea water is about 1025 kg/m, while the density of pure ice is about 920 kg/m³. Another unusual feature of water is that, while most substances contract when they cool, (just ask your husband after he goes for a 'polar plunge', and he'll tell how small things can get when it is cold!), wacky water expands when it goes below about 4 degrees. So when water solidifies i.e.; freezes, it floats - as ice.

Ice is not always nice. It is not always pure white. Green ice can be caused by a green algae called Chlamydomonas nivalis. Red ice, also known as ‘Watermelon Ice’ (because it smells like watermelon?) may also be known as ‘Blood Snow’, ‘Raspberry Snow’. This can be caused by the same green algae as it also has a secondary red carotenoid pigment, called astaxanthin. This protects the algae from ultraviolet light, absorbs energy to melt snow, which then provides the algae with liquid water. In Antarctica around penguin colonies the snow can also be stained red or pink by their poo, coloured from their diet of krill. Brown & Black Ice (Dirty ice) is often due to soil or volcanic sand (as in above image), but in areas of human habitation, it can be the result if various pollutants.

Phylum Arthropoda

Subphylum Crustacea

Order Euphausiacea: 'Krill'

Euphausia spp.

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

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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