The main reason why marine animals are able to grow so large is because water provides buoyancy, which supports massive body weights, says Will Newton.
This force works against gravity and means that marine animals don’t need thick, heavy bones to support themselves, like those that live on land do.
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Another reason why living underwater favours giants is thermoregulation. The larger an animal is, the smaller its surface area-to-mass ratio. This is key for retaining core body heat at the poles where water temperatures regularly drop below freezing, as well as in the ocean’s dark, gloomy depths.
In the deepest parts of the ocean, the metabolic rates of animals slow down dramatically. While this means they grow slowly, it grants them sustained, uninterrupted periods of growth that can last decades or even centuries. This is one of the main driving forces behind deep-sea gigantism and the reason why colossal squids, greenland sharks, oarfish, and other strange, deep-sea behemoths exist.
There are also abundant energy sources in the ocean. Yes, the open ocean may often be described as a ‘marine desert’, but there are areas of deep-sea nutrient upwelling where small, energy-dense prey like krill congregate in their billions.
These ‘ocean oases’ are veritable buffets, particularly for filter-feeders like baleen whales, and provide the immense amount of calories needed to sustain giant body sizes.The factors that facilitate gigantism in the ocean aren’t just affecting animals now, they’ve affected animals ever since the emergence of complex life roughly half-a-billion years ago. In the last few hundred million years, the ocean has seen many giants come and go (and some stick around until the present day.
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Top image: Sperm whale by Mike Korostelev / Getty Images
