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Blue blood on ice -- how an Antarctic octopus survives the cold

March 10, 2015

An Antarctic octopus that lives in ice-cold water uses an unique strategy to transport oxygen in its blood, according to research published in Frontiers in Zoology. The study suggests that the octopus's specialized blood pigments could help to make it more resilient to climate change than Antarctic fish and other species of octopus.

The Antarctic Ocean hosts rich and diverse fauna despite inhospitable temperatures close to freezing. While it can be hard to deliver oxygen to tissues in the cold due to lower oxygen diffusion and increased blood viscosity, ice-cold waters already contain large amounts of dissolved oxygen.

In Antarctic fish, this reduces the need for active oxygen transport by blood pigments (e.g. haemoglobin), but little is known about the adaptations employed by blue-blooded octopods to sustain oxygen supply in the cold.

Lead author Michael Oellermann from Alfred-Wegener-Institute, Germany, said: "This is the first study providing clear evidence that the octopods' blue blood pigment, haemocyanin, undergoes functional changes to improve the supply of oxygen to tissue at sub-zero temperatures. This is important because it highlights a very different response compared to Antarctic fish to the cold conditions in the Southern Ocean. The results also imply that due to improved oxygen supply by haemocyanin at higher temperatures, this octopod may be physiologically better equipped than Antarctic fishes to cope with global warming."

Octopods have three hearts and contractile veins that pump 'haemolymph', which is highly enriched with the blue oxygen transport protein haemocyanin (analogous to haemoglobin in vertebrates).

To find out what makes the haemocyanin of an Antarctic octopus so well-adapted to cold water, the researchers collected and analyzed the haemolymph from the abundant Antarctic octopod species Pareledone charcoti, and two octopod species collected from warmer climates - the South-east Australian Octopus pallidus and the Mediterranean Eledone moschata.

The Antarctic octopus Pareledone charcoti had the highest concentration of haemocyanin in its blood - at least 40% more compared to the other species, and ranked amongst the highest levels reported for any octopod. The researchers say that these high blood pigment concentrations may be compensating for the haemocyanin's poor ability to release oxygen to tissues while in cold environments, and could help to ensure sufficient oxygen supply.

The Antarctic octopod haemocyanin was also found to shuttle oxygen between gills and tissue far better at 10°C than at 0°C. At 10°C the Antarctic octopod's haemocyanin had the potential to release far more oxygen (on average 76.7%) than the warm-water octopods Octopus pallidus (33.0%) and Eledone moschata (29.8%). This ability may help the Antarctic octopod tolerate warmer temperatures in addition to the cold, and may link to the life style of Pareledone charcoti, which is also reported to reside in warmer shallow waters and rock pools.

Considering the strong warming trend at the Antarctic Peninsula, Pareledone charcoti may eventually benefit from its capacity to adjust blood oxygen supply to more variable temperatures than other species, including Antarctic fish.

The new findings show how the blood pigment haemocyanin in octopods is able to support oxygen supply in both cold and warm environments, and could help explain why octopods remain so populous across a wide spectrum of ecological niches.

While haemocyanin has proved to be crucial to Antarctic octopods, more comprehensive insight is needed to predict their fate in a warming ocean.
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Notes to editor:

1. Photos and videos of Antarctic octopods in the wild can be found here: http://bit.ly/1B7zbgU

All photos and videos must be credited as provided in the filenames, and permission for use requested by first contacting tomas.lundalv@loven.gu.se and armin.rose@senckenberg.de

2. Research article

Michael Oellermann, Bernhard Lieb, Hans O Pörtner, Jayson M Semmens and Felix C Mark
Blue blood on ice: Modulated blood oxygen transport facilitates cold compensation and eurythermy in an Antarctic octopod.
Frontiers in Zoology 2015

DOI: 10.1186/s12983-015-0097-x

To receive an embargoed copy of the research article, please contact Joel.Winston@biomedcentral.com

After embargo, article available at journal website here: http://dx.doi.org/10.1186/s12983-015-0097-x

3. Frontiers in Zoology is the first open access journal focusing on zoology as a whole. It aims to represent and re-unite the various disciplines that look at animal life from different perspectives and at providing the basis for a comprehensive understanding of zoological phenomena on all levels of analysis. Frontiers in Zoology provides a unique opportunity to publish high quality research and reviews on zoological issues that will be internationally accessible to any reader at no cost.

4. BioMed Central is an STM (Science, Technology and Medicine) publisher which has pioneered the open access publishing model. All peer-reviewed research articles published by BioMed Central are made immediately and freely accessible online, and are licensed to allow redistribution and reuse. BioMed Central is part of Springer Science+Business Media, a leading global publisher in the STM sector. http://www.biomedcentral.com

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