A Bunch of Icefish in the Weddell Sea

Interesting stuff:

A breeding colony of 60 million fish has been discovered in Antarctica's ice-covered Weddell Sea -- a unique and previously unknown ecosystem that covers an area the size of Malta.

...The vast colony, believed to be the world's largest, is home to the remarkable icefish (Neopagetopsis ionah), which has a see-through skull and transparent blood. Icefish are the only vertebrates to have no red blood cells.

To survive at such low temperatures, it has evolved an anti-freeze protein in its transparent blood that stops ice crystals from growing.

...The breeding colony was discovered in February 2021 by the German polar research vessel Polarstern, which was surveying the seabed about half a kilometer below the ship. It used a car-sized camera system attached to the stern of the ship that transmits pictures up to the deck as it's being towed.

..."We just saw fish nest after fish nest for the whole four hours, and during that time we covered maybe six kilometers (3.7 miles) of the sea floor," said Autun Purser, a postdoctoral reseacher at the Alfred Wegener Institute in Bremerhaven, Germany. He's the lead author of a study on the icefish colony that published in the journal Current Biology on Thursday.

...The colony covers more than 240 square kilometers (93 square miles), the researchers said. With, on average, one nest for every three square meters, they estimated that the colony includes about 60 million active nests.

..."Some animals like to be social, but there's a limit. Congregating may give them advantages for finding mates but provides a rich point source for predation."

The fish appear to be attracted by an area of warmer water, which is around 2 degrees Celsius warmer than the surrounding sea bed, which is a chilly 0 degrees Celsius, said Purser. (Sea water freezes at a lower temperature than fresh water.)

...The findings reveal a globally unique ecosystem, according to the researchers, and they say it should be designated a protected area. ...While the Weddell Sea is covered with sea ice all year round, the ice is relatively thin -- three feet thick -- meaning that photosynthesis can still take place and life can thrive. Purser said the Weddell Sea floor is far from barren, with sea sponges, corals, octopuses and star fish lurking along the seabed.