31: Life in the Arctic Ocean

Over the last 30 or so plogs, we have looked at all kinds of aspects of life in the Arctic. However, they have all been a little biased towards life on land, so this week we’re going to take a look at the life living under the sea! This will include microscopic crustaceans, jellyfish, whales, and a toxic big old creature thought to be the species with the longest known lifespan among vertebrates! Curious to see who takes the title? Read on…

A map showing the Arctic Ocean (Picture: Encyclopaedia Britannica)

Flora

Plants make up the basis of most life on land, capturing the energy of the sun and allowing animals to use this energy by eating them. The sea is no different, with plants making up the bottom of the food chain there too. However, the Arctic Ocean is a pretty intense environment covered by ice for much of winter and experiencing violent storms, so picturesque warm loving species like corals aren’t found in this region. Instead phytoplankton make up the majority of plant life. I have done a full plog on phytoplankton before (5: Phytoplankton- Lungs of the Ocean) but for a brief overview, they are tiny, often microscopic plants who despite their size and lack of fame are actually responsible for creating half of the worlds oxygen, the other half being made by all the plants on land.

During the brief Arctic summer, phytoplankton works hard to convert sunlight into energy for themselves to grow, and do this either whilst floating out in the open ocean or by living in a more basic form as algae on the underside of ice sheets which cover the water. Despite their tiny size, there are trillions of them, and so they are able to be a sustaining food source for pretty much all of life in the area.

Other than phytoplankton there really isn’t much other plant life. Seaweed can be found across the Arctic Ocean, being hardy enough to survive the cold and storms, but whilst it provides important shelter for fish in the area, it is not a source of food for underwater creatures. At low tide however, it can be used as a food source by animals above water such as reindeer or muskox.

The greenish tinge is this photo is created by phytoplankton living under the ice (Photo: WESTEND61/GETTY IMAGES)

Fauna

The next step up in the food chain are the little creatures that eat phytoplankton. The main type is zooplankton who float in the oceans surviving off both phytoplankton and detritus like dead fish. Zooplankton isn’t a particular species, but more a broad group of animals including crustaceans like copepods and krill, and molluscs like clams. Across the world’s oceans there is estimated to be around 500 million tonnes of krill, so they make up for size in numbers.

Jellyfish like the Lion’s Mane jellyfish are also found in Arctic waters, and can be anything from 50cm to 2meters in size. Whilst floating along with the currents they are also used by some creatures like shrimp as a little oases. The shrimp can feed off scraps and use the jelly’s stingy reputation as protection from predators.

All these little creatures (well, the Jellyfish might not be so little…) are eaten by bigger fish like herring, cod and capelin who cruise the oceans in groups. They are in turn eaten by top predators including seals like the harp and ringed seals, whales, polar bears and walruses. It should be noted though that many baleen whales, the ones with the bristle like teeth which includes species like the bowhead whale, rely on the smaller creatures like krill for food, rather than eating bigger fish.

Many of these animals are migratory, moving to warmer waters when the Arctic Ocean gets too iced up and the lack of sunlight in winter means that phytoplankton isn’t growing. In fact of all the whales that venture north, belugas, narwhals and bowhead whales are the only ones to stay in the Arctic Ocean year round.

Just a little side note, penguins are only found in Antarctic, not the Arctic. There are birds who live on land but hunt in the Arctic waters like fulmars, guillemots and kittiwakes, so they probably deserve a mention for being brave enough to dip their beaks in.

On the left a very zoomed in picture of krill (Picture: Øystein Paulsen/Wikimedia), and on the right a Beluga whale (Picture: Salva Barbera and Sheila Sund)

Greenland Shark

One of the lesser known but pretty amazing inhabitants of the northern oceans are Greenland shark, also known as grey sharks. They are one of the largest shark species, anywhere from 2.5m to 7.3m in length and 400kg to 1,400kg in weight, though most are on the lower end of these scales. They are also one of the longest living vertebrates (animals with backbones), thought to only reach sexual maturity at 150 years. The oldest aged individual is thought to be around 392 years old (or within 120 years older or younger than that, they are hard to age).

The Greenland shark doesn’t stop being notable here, they also have toxic meat which has a high content of urea (a chemical found in urine) and trimethylamine oxide which help it deal with the water pressure when it wanders down to depths of at least 2,200m. You would think having toxic urine-like flesh would put people off eating it, but the shark meat, when treated to reduce toxin levels, is a delicacy in Iceland known as kæstur hákarl.

This creature rounds off its rather impressive set of accolades with its diet. Though they mostly live off fish like cod and capelin, remains of seals, polar bears, moose and even an entire reindeer have been found in the body of Greenland sharks. It is also a scavenger, so might feed off already dead animals and fish waste off fishing boats. There are no known attacks of humans by this behemoth, but then again people tend not to swim in the Arctic Ocean as it is so cold, so given the chance maybe they would snack on you.

A Greenland shark cruising the waters. Picture: picture-alliance/dpa/Ocean Image

Currently the Arctic Ocean is now also trying to battle with radioactive contamination, melting sea ice and an influx of freshwater from this melting sea ice, how this will affect the ecosystems under the water remains to be seen. From microscopic blobs that harness the energy of the sun whilst lazily drifting through the ocean, to giant ancient toxic predators prowling the deep, the Arctic Ocean is full of a diverse and incredible set of creatures many of whom we are still only starting to learn about today.

For more info:

The scientific paper in which they try to age the shark: https://science.sciencemag.org/content/353/6300/702

A Nat Geo video on the Arctic Ocean:

Music: kongano.com

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