Deep-sea gigantism

In zoology, deep-sea gigantism, also known as abyssal gigantism, is the tendency for species of invertebrates and other deep-sea dwelling animals to display a larger size than their shallower-water relatives. Proposed explanations involve adaptation to scarcer food resources, greater pressure or colder temperature at depth.

Examples of deep-sea gigantism include the giant isopod, the giant amphipod, the Japanese spider crab, the king of herrings (an oarfish of up to 12 m), the deepwater stingray, the seven-arm octopus, and a number of squid species: the colossal squid (up to 14 m in length), the giant squid (up to 13 m), Onykia robusta, Taningia danae, Galiteuthis phyllura, Kondakovia longimana, and bigfin squids. Some other very large fish found in the deep ocean, such as the Greenland shark and the Pacific sleeper shark, would not normally be considered examples because they sometimes visit the surface and are not larger than comparable species that spend more time in shallower water, such as the Blacktip Reef Shark and Mako Shark whose average lengths are about 8.4ft and 10 ft.

It is not known whether deep-sea gigantism comes about as a result of adaptation for scarcer food resources (therefore delaying sexual maturity and resulting in greater size), greater hydrostatic pressure, or for other reasons.

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