Crabs - The Fall of Karkinos
Rosie Brown
Many of us have spent time alongside the rocky shore, bucket and net in hand, wading through the rockpools as we turn over clumps of seaweed and large rocks in the hopes of finding tiny marine creatures. Shrimps and fish, iridescent periwinkles, anemones, and all sorts of oddities to fascinate us. Then, we glimpse something scuttling across the sandy floor – we reach out, submerging our arms up to our elbows as we try and grasp the beast. Fingers frozen from the cold; we fumble around for a grip as we carefully bring it out from its hidey hole.
Shore Crabs. Photo: Saskia Sicherman
A beautiful shore crab, shining green with its claws raised in annoyance. A dweller of the coast, a scavenger with an attitude. These animals are common finds along the UK shoreline, and are always a delight to discover lurking beneath a rock or buried under seaweed. Finding these stunning creatures is always a great joy, one that has brought many smiles to the faces of avid rock poolers.
The shore crab is just one of the many found along British shores, with over 60 crabs calling the British Isles home. Yet, worldwide, there is over 5,000 species residing in our oceans, rivers and even on land. These many species vary in shape and size, from the tiny pea crab being a few millimetres wide, to the Japanese spider crab with a leg span of up to 4 meters. They are invertebrates with their exoskeleton providing support for their bodies, as well as protecting them from predation.
Hermit crab. Photo: Unsplash
Crabs stem from the order Decapoda, this includes other groups such as crayfish, lobsters, shrimps, and prawns to name a few. It is important to note that not all crabs are in fact ‘true’ crabs – hermit crabs, horseshoe crabs, king crabs and porcelain crabs are grouped as Anomura, all true crabs belong to the sister group, Brachyura. Crabs are without a doubt a vital part of the marine ecosystem, acting as the ocean’s cleaners as well being a crucial component to the food chain. Crabs are not just loved by ocean dwellers, but by us too. They have long been considered a delicacy in many regions and are known for their delicate flavours and enjoyable taste.
Shore crabs. Photo: Saskia Sicherman
However, their significance in our culture and society is not just focused on their importance as a food source. Throughout history, these crustaceans have played roles within mythology and religion. The constellation, Cancer, is said to resemble a crab, the crab is question being named Karkinos. This goliath sized crab is said to have come to the aid of Hydra in its battle against Hercules. Hera, goddess and wife to Zeus, sent Karkinos to distract Hercules to give Hydra the advantage. Yet, the monstrous crab failed and one kick from Hercules shattered Karkinos shell. As a reward for giving up its life, Hera placed the crab among the stars as the constellation, Cancer. Coincidentally, this constellation is close to the constellation Hydra.
Of course, it is unlikely that we will ever see crabs of such size (though over 80% of the ocean remains unexplored, so who knows) yet the unfortunate reality is that crab shells are disintegrating, though not due to a Herculean force.
Ocean acidification is the result of our oceans absorbing mass amounts of carbon dioxide. While this process is natural, the burning of fossil fuels has increased the levels of carbon found in the atmosphere - this of course applies to water as well. According to the National Oceanic and Atmospheric Administration (NOAA), it is estimated that up to 30% of all our carbon emissions released into the atmosphere is absorbed by the oceans. This imbalance is resulting in lower pH levels which is causing the bleaching of coral reefs, and now the demise of crabs.
Bleached rock pool. Photo: Saskia Sicherman
As briefly touched upon, crabs have exoskeletons which protect and support their bodies. However, ocean acidification is resulting in these degrading – their shells are becoming brittle; and then breaking. It is an indicator of our changing seas; a change that for many species could bring upon disaster. Yet given the importance of crustacean’s role within the marine world, a decline in their populations could prove to be even more disastrous.
Dead crab in the sand. Photo: Unsplash
Studies on both captive and wild crabs have revealed similar outcomes when it comes to an increase in ocean acidity. In the past, it was thought that crustaceans would be less sensitive to ocean acidification – however, this is not the case. Recent studies appear to show acidification having a major impact on their early life stages, with many dying prematurely due to their disintegrating shell. The effect of acidity on adult crabs is still very much unknown, though it has been theorized among researchers that bizarre behaviour patterns found across various species could be a result of ocean acidification.
However, one study reveals that all might not be lost for the crab. Robert Foy, director of the Alaska Fisheries Science Centre’s Kodiak Laboratory, has been conducting long-term studies on the effects of acidification on Red King crab. These large, spiny crabs reside in the north of the Pacific, an area that is sensitive to the effects of acidification due to its oceanography.
Foy replicated water conditions that follow the predictions for Alaska’s waters in the next few decades. His studies revealed that the majority of King crab did not survive past their early life stages. However, a small handful did survive the more acidic water. This indicates there is a possibility that crabs will be able to adapt to a more acidic environment.
Bleached Corallina weed. Photo: Saskia Sicherman
So, the question now is whether crabs will be able to survive a changing climate, or yield to a fate like that of Karkinos? Hopefully today’s crabs will adapt to this changing world and continue to lurk in the ocean’s depths, hiding in the rock pools to be discovered by the future generation of rock poolers.
Crab sitting in a hand. Photo: Unsplash