They Might Be Polar Giants

Latitude: -062 40.4665  Longitude: -049 58.6846

With a week of sampling under our belt, and now having seen some really cool marine invertebrates, one of the things that has been on my mind lately is just how large the critters can be! Animals living in the Arctic and Antarctic can have unusually large body sizes compared to those in warmer waters – this phenomenon is known as polar gigantism. A similar phenomenon, abyssal (deep-sea) gigantism, is when organisms are larger at depth than those closer to the surface.

There are several possible explanations for gigantism. For instance, invertebrate body sizes are limited by how much oxygen is available in the water – since more oxygen can be held in cold water, body size is able to increase. Metabolism also isn’t as fast in colder waters, so while size may ultimately be larger, the animals live longer and grow more slowly. Bigger body sizes can help guard against starvation, so it might be beneficial in that way. Both slow metabolism and resistance to starvation allows polar organisms to withstand periods without food due in low productivity waters. Another factor leading to bigger body sizes could be less predation. Not getting eaten means more time to grow! All of the above have probably been in play over the course of millions of years, evolving certain groups to get larger and larger because the benefits outweigh the risks.

In any case, we have seen a lot of big animals and I think we’ll be seeing a lot more. There are large amphipods, sea spiders, sea mice, sea stars, sponges, and leeches, to name a few! Every time our sampling equipment returns from the depths comes new excitement for what we might find. Sometimes it’s hard to resist not going out on the main deck during off-shift hours to get a first look every time we pull in a trawl or epibenthic sled – we can call this FOMO (Fear of Missing Octopuses) or FOMF (Fear of Missing Fauna).

I look forward to the next three-ish weeks of sampling and all the Icy Inverts left to see!

Megan McCuller
Collections Manager, Non-molluscan Invertebrates
North Carolina Museum of Natural History