• Diane

A King Crab's Southward Journey

van Rooyen, G. A King Crab’s Southward Journey. 4 April 2019. Map sourced from LINK PD

Sometime, not long before 2010, a heroic King Crab would have taken its first steps into the Southern Ocean. She most likely didn’t realize that she was the first in about 40 million years to do so, but who am I to know what a King Crab thinks about. Perhaps she boarded a tourism ship to Deception Island, or she could have fought her way through the turbulent currents of the Polar Front, or perhaps she passed through the front as just a tiny larva, able to be swept through in a warm pocket of water. If it were one of the first two options, then only she had managed to it make it through, if she was already impregnated. If the later, then at least two larvae must have managed the journey. Either way, she managed to set up the viable populations now present, working their way up the continental slope towards the shelf.

However hard the journey was, it was a great success for the King Crab. The Southern sea floor was King Crab bliss, absolutely covered in prey for them. Having had no predators for millions of years, the local shell covered invertebrates lost their defenses, an unnecessary expense for them to continue producing. They were able to diversify and form a vast array of beautiful and unique fauna. This is great news for the King Crab. Not only is food plentiful and easy to take, but it is all theirs and they are prey to no one.

Not such good news for the previous seafloor community, however. It’s going through quite a change. From a very unique ecosystem to a seafloor that looks like all the other seafloors around the world where predators keep these hard-shelled species in check. Extinctions are happening at alarming rates here. The sections of seafloor where King Crab populations have been found have already changed dramatically, and over the next few decades, it is expected they will have finished their migration up the continental shelf and be the true “Kings” of the ecosystem.

Seawall Seafloor Antarctica: Sourced from LINK

When the first King Crab was found in the Southern Ocean in the summer of 2010, it set off plentiful research about how they came to be there. The answer was clear. The oceans are warming, at an even faster rate than we are experiencing on the surface. The Polar Front which was once thought of as an impenetrable fortress, that used to expel any invaders is not as strong as it once was. Both of these are attributed to anthropogenic climate change. King Crabs would have never been able to survive the much colder waters of the Southern Oceans previously. The reason they have been excluded is like their relatives they can not regulate magnesium in their blood at lower temperatures. Luckily, King Crabs have an advantage. They can hypometabolise allowing them to survive non-ideal temperatures by slowing down their life-cycle. This is likely why they are first on the scene. Even with this advantage, they couldn’t survive the much too cold waters before, but now the deeper waters of the Southern Ocean are within their tolerable range, and the shallower waters will be within the next couple of decades.

Global Warming: Change in the Earth’s Total Heat Content. Sourced from LINK

King Crabs are not the first, and will not be the last, species to change their range due to warming temperatures. Many others have had new lands opened up to them and have moved pole-wards or up in elevation to areas previously unsuitable to them. They have become invaders to an ecosystem that developed in their absence, and with the changes happening much more rapidly than natural warming cycles, the natives of those areas cannot possibly hope to adapt in time.

What we can do about these aggressive predators remains unclear. Removing the Crabs from the Southern Ocean would be a huge undertaking, but as I’ve said, they are just one example among a multitude of species doing the same and wreaking havoc on ecosystems along the way. We may not be able to return all these species to their home range, but we should see it as a warning, as this is a trend that will only continue. The more stories that come up about how one species is impacting millions of others, the more seriously the issue will be taken. Maybe seafloor invertebrates are not the most charismatic species to get people riled up about this issue, but there is something so pristine about Antarctica. The fact that it is so far from our modern, civilized, emissions producing world and seeing these kinds of impacts should make us think about how far-reaching these implications are.

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