Origins ANTARCTICA, Scientific Journeys from McMurdo to the Pole
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Fish: Fresh, Not Frozen

A Species Cornucopia
We left our story off when Antarctic marine fish without antifreeze proteins disappeared, and one ancestral antifreeze-carrying Notothenioid species remained.

The Notothenioids had a great ecological opportunity. Because the Antarctic seas were mostly empty of fish, they had minimal competition for food or habitats. Exploiting this ecological vacuum, the Notothenioid populations ballooned in size and migrated into the region’s different habitats (such as the surface ice cover and ocean-floor spongebeds), breaking up into different subpopulations.

Over time, the subpopulations adapted to the unique features of each habitat, eventually becoming different enough to turn into new species. These adaptations resulted in an explosion of more than 90 new Notothenioid species that predominate in the Antarctic ecosystem today.

In the language of ecology, this species expansion is known as adaptive radiation—broadly defined as the process of a "parent" species colonizing empty habitats and multiplying into new species.

Bald notothen (Pagothenia borchgrevinki)

Bald notothen (Pagothenia borchgrevinki)
(click for a larger image)

© Danette St.Onge

Threadfin pithead (Aethotaxis mitopteryx)
Threadfin pithead (Aethotaxis mitopteryx)
(click for a larger image

© Danette St.Onge
Of these two Notothenioids, the threadfin pithead lives in deep-sea habitats (about 2000 feet deep) while the bald notothen lives along the underside of the surface ice layer, often burrowing inside the ice. Comparing the illustrations reveals how adapting to different habitats can result in different body features.

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