A week or two ago, my good friend, Mr David Wells B.A. (Hons), and I got onto the topic of deep sea gigantism. To the casual reader, this may seem an absurd topic of conversation and for the life of me I can’t remember how we got on to it. However, such conversations are all to frequent between our group of friends; admittedly I am mostly to blame. Never the less, I feel that deep sea gigantism merits a revisit, especially as it gives me a chance to post some photos of the most charmingly hideous creatures known to man. Pardon the pun, but I’ll dive right in.
This many legged friend is a Giant Isopod. It’s a type of crustacean closely related to woodlice. Here it photographed next to a bewildered cat for the entertainment of some Chinese people.
Here is another frightening arthropod. The Japanese Spider crab, photographed here with a smiling man scale bar, can attain a leg span of 3.8m.
Many deep sea squid species attain a colossal size. The biggest of them all is the appropriately named Colossal Squid (Mesonychoteuthis), which can be found in the Southern Ocean. The photo above was originally believed to be first image of the elusive giant squid (Architeuthis). It has since been re-identified as a Robust Clubhook Squid, another large squid species.
It's not just invertebrates that grow to extreme size in the deep. Vertebrates too can attain monstrous proportions. The Pacific Sleeper Shark and the bizarre Megamouth Shark rival the Great White in length. However, the champion of champions, and my personal favourite, is the King of Herring (pictured above). It’s a species of Oarfish, which are essentially elongate bony fish (unlike sharks which have cartilaginous skeletons). The King of Herring is listed by Guinness as the longest bony fish in the world and can reach a whopping 17m.
Deep-sea gigantism is when some animals become much larger than their shallow-water or terrestrial relatives. The question is why gigantism is commonplace in the ocean depths. There is a general consensus that limited food availability plays a crucial role in encouraging gigantism in the deep sea. Competition for limited resources results in natural selection of an optimal body size for a particular habitat. In many ways, this idea is similar to that of Island gigantism (e.g. Galapagos Giant Tortoises). However, the key difference is that Island gigantism relies on the removal of typical apex predators and dominant herbivores (e.g. large mammals) leaving other organisms free to increase in size. Such a situation seems less likely within oceans. After considering this, it seems paradoxical that a constrained food source would result in larger body size within the deep sea realm. However, I think the fact that the cause of deep sea gigantism remains a mystery only enhances the enigma of these denizens of the deep... And yes, that was a magic the gathering reference.
