Gigantic!

Cold water gigantism refers to the phenomenon where some species of marine organisms, such as invertebrates and fishes, found in cold water environments grow to unusually large sizes compared to their counterparts in warmer waters. It is believed to be an adaptation strategy that helps these organisms survive in the challenging conditions of colder habitats.

Cold water gigantism is not fully understood, but it could be that the lower metabolic rates in cold water slow down an organism's growth rate, allowing them to allocate more energy towards achieving larger sizes. Perhaps also the higher oxygen content and nutrient availability in colder waters may contribute to larger species.

Another theory suggests that the reduced predation pressure in cold water environments allows for the survival and growth of larger individuals. Larger sizes can provide benefits such as increased buoyancy, improved cold resistance, and better competitiveness for resources.

In our chilly waters off the coast of Vancouver Island we are neighbours with the largest species of nudibranchs (orange peel nudis), the largest sea star (sunflower seastar), the largest known species of octopus (giant pacific octopus), the longest jellyfish (lion’s mane) and some pretty hefty dinner plate sized sea anemone species. I don’t know if the same theory applies to cold water divers vs. warm water divers but I certainly use extra insulation and better buoyancy as a reason to eat more cookies.

Check out the paper: Polar gigantism and the oxygen–temperature hypothesis: a test of upper thermal limits to body size in Antarctic pycnogonids to learn more