New life in sea and rivers
Antarctic seas are facing a big crisis. Warming waters have caused the collapse of krill biomass, causing a great local extinction. The increase in temperature also impacts the circumpolar currents, which start becoming weaker and weaker, mixing with the South Atlantic one. Whales have been severely reduced, while other medium-sized vertebrates have taken advantage of this. Lots of sea organisms have then tried to move towards a new growing habitat: the freshwater rivers and lakes of Polarica
Giant seal of the kelp forest
Kelp forests are now the richest and most biodiverse marine habitat around Antarctica. It can be found in relatively cold and shallow waters, where large algae of even 30 meters can grow. This habitat gives shelter to a multitude of large herbivorous fish, crustaceans and several species of dolphins. With the local disappearance of large predators, an already large carnivore had its chance to become even larger.
We're talking about the Shark seal (Phocetus glacialis), a descendant of the leopard seal that can exceed 1 ton of weight (2205 lb). Compared to its smaller ancestor, the shark seal possess a longer and stronger snout, to increase its bite range, while maintaining the same bite force. The entire body is also way longer proportionally, with wider feet to increase its speed. It's an ambush predator that hunts any large vertebrate of the sea. For large prey, like whales and dolphins, the shark seal uses its strong jaws to rip off pieces of flesh. that severely injures the cetacean. They firstly bite the fins, slowing down their prey, and then they start to damage their blowhole.
The shark seal is the first seal lineage adapted to live completely out of the land: shores are never reached by this beast, despite larger holocenic pinnipeds being completely able to do that. When females give birth, they move temporarily to coastal water: youngs are born extremely precocial, being able to move and breathe instantly. The mother's milk is sprinkled in the water like cetaceans do.
Bizarre riverine hosts
Despite antarctic rivers usually freeze on the surface during winter, life continues under the ice. Some species adapted to feed in ice holes, like the diving pipit, but other species have adopted different strategies to survive.
The River shag (Leucocarbo criofluviatilis) for example, is a cormorant species that seasonally migrate away from Antarctica when the cold season approaches. It is the only long-distance migratory cormorant ever known, feeding only in freshwater habitats, without competing with its marine counterparts. Despite not being a pretty large species (it's a small-medium sized species for being a Phalacrocoracid) its ecological behavior makes it a very unique and amazing species to add to Antarctica's biodiversity.
Another very interesting species of bird from Antarctica is a new clade of penguins that have become durophagous and moved to freshwater habitats: meet the icekisser (Foraminus ameryensis)! Oppositely to the river shag, icekissers remain all year in freshwater, eating arthropods that live on the river bed. To hunt them, crab penguins use their long and sensitive rictal bristles like whiskers, rummaging the bottom of rivers and lakes in search of crabs, shrimps, insects and fish.
Since lots of antarctic rivers are relatively small for supporting large populations, icekissers faced several eco-physiological adaptations: firstly, they've reduced drastically their size, weighing less than 800 grams when adults (1,7 lb). Secondly, icekissers have a great dispersion rate in their environment.
Since a land migration would be extremely dangerous for them, icekissers migrate by returning to the sea and following the coastline to go up to another river. In this way, populations that live in small rivers still possess a good genetic diversity thanks to this strong gene flow. Nests are made on riverbanks by digging a hole, sometimes connected to the river underground as an emergency escape. These long burrows are principally created by using their strong and short beak as a shovel. Rounded wings and wide feet help to move away the loose soil.
They can be seen often basking near rivers in groups of hundreds, always on alert for ground predators.
The name "icekisser" refers to the habit of this penguin to break the ice of superficially frost rivers with their beak. This is made to always have a point to breathe air when submerged during winter. This indirectly helps foraging birds like the diving pipit.