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Scientists discover 60 million icefish nests - the largest known breeding colony in Weddell Sea

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Icefish nests numbering 60 million were discovered by scientists in the Weddell Sea, with each of them guarded by an adult (Pictures Courtesy livescience.com)

It was indeed a bonanza for the researchers onboard the German icebreaker, RV Polarstern as they came across a treasure of 60 million icefish nests spread on the Weddell Sea floor. Guarded by a parent, it is the largest known breeding colony of fish.

As per an article in livescience.com, stationed on the bridge of the ship and keeping a watch for whales, Alfred Wegener Institute’s Autun Purser was called by Lilian Bohringer, his graduate student, when the latter monitoring the camera observed the nests. Among the missions of the ship is to monitor Weddell Sea’s seafloor and it is done with the Ocean Floor Observation and Bathymetry System (OFOBS), a one-tonne camera towed behind the ship.

The student had seen fish nests spread all over the seafloor in all directions – one about every 10 inches or 25 centimetres. The area covered by the nests was 240 square kilometres or 93 square miles.

Bohringer told Live Science: "The camera was moving [across the seafloor] and it just didn't stop. They were everywhere.”

The contour of the nests was like that of modest bowls carved in the seafloor mud by notothenioid icefish or Neopagetopsis ionah. Native of chilly southern oceans they are only known vertebrates who lack haemoglobin completely in their blood and that is why they are considered "white-blooded”. They probably are the prey for the Weddell seals inhabiting that region.

Talking about this discovery, Purser said: "We realised after ringing up the home institute the next day that we had found something spectacular.”

An elder icefish seems to be guarding each of the nests

Following the discovery, the ship passed that area many times, taking the camera to a shallower depth for a better and wider view of the colony. After an extensive survey, it was estimated that there were 60 million nests there, each with more than 1,700 eggs and appearing to be guarded by an adult fish. Along with the nests there were fish carcasses too.

The scientists happened to be in that region to study a water upwelling which was warmer than the surrounding area water by two degrees Celsius. Explaining their mission, Purser said: "Our aim was to see how carbon goes from the surface to the seafloor and what communities are in the water column.”

Also read: Scientists use smart Seals to reveal secrets of the Antarctic

What they found during their study of the water column was microscopic zooplankton close to the surface. These became the diet of the freshly hatched icefish, who would return to the seafloor to breed after eating them. While it was foreseen that icefish would be found in the upwelling, a  breeding of the size discovered was definitely not on the cards.

The icefish carcasses found around the nests suggested that they played an important part of the food chain by serving as a prey for the Weddell seals.

The find of such a big nesting colony has propelled an initiative to make the area a Marine Protected Area under the international Commission for the Conservation of Antarctic Marine Living Resources.

An interesting observation noted about the colony was that it had a boundary. Elaborating on this Purser said: "[The colony] went from very, very dense to nothing, much like penguin colonies. It was like a line in the sand."

Also read: Antarctica’s magical and majestic penguins, eagles and seals captured by Dr. Huilgol photographs

The boundary turned out to be warm upwelling’s outer edge and this, scientists feel requires a separate detailed study.

Keen to know more about this ecosystem, the crew of Polarstern has left two cameras as they have plans to return in April this year.

The findings of this study made it online in the journal Current Biology.