Mollusk With The Longest Lifespan

The longevity of animals can range from only a few days (for adult mayflies), to hundreds and hundreds of years for others, and we often find surprises when we look closer at how long different animal species live for.

I wrote about the vertebrate with the longest lifespan a little while back, where the Greenland shark (Somniosus microcephalus) has been suggested to be able to be as old as 392 ± 120 years. There's a huge margin of error there, but it could potentially be a bit over 500 years old, although it's more likely that it's closer to 400.

In today's post we will be looking at an animal that is certainly over 500 years old, and this time it's not a huge whale or anything like that, but instead a rather small marine mollusk - the ocean quahog (Arctica islandica). An ocean quahog. You have probably seen the shells from them if you have been to a beach connected to the North Atlantic Ocean.

The ocean quahogs are a species of edible clams that are native to the North Atlantic Ocean, where they are pretty common.

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They have very few natural predators, except for the wolffish (Genus Anarhichadidae) that have been shown to be capable of crushing their shell. A wolffish, the only natural predator to the ocean quahogs. Image is Public Domain. Since they have very few natural predators, some ocean quahogs have grown to become very old, and in fact they hold the record for the world's oldest known animal among them. If you eat these clams, then you might actually eat meat from a clam that is several hundred years old, which is kind of weird to think about if you ask me.

The life cycle of an ocean quahog A young ocean quahog grows slowly, and about 12-13 years after it was born it becomes fertile. During this time it will be able to spawn with another member of its species, and it will be able to do so for another 12-13 years. At this time (around age 25) most of the quahogs will stop reproducing, and instead enter a state of negligible senescence. While negligible senescence sound complex, it pretty much just means that the organism have stopped aging at this point. From here on out it just lives its life without aging any further. This trait is rather uncommon in the animal kingdom, as most animals tend to get weaker the older they get. Animals that exhibit negligible senescence do however have a constant death rate, meaning that a 300 year old individual do not have a higher change of being killed than a 50 year old individual. Most animals do obviously have an increased mortality rate that increases exponentially as they grow older. This is what typically determines the upper limit to their longevity, but the animals that exhibit negligible senescence could live a lot longer than we expect them to.

During a dredging operation off the northern coast of Iceland in 2006, the research vessel Bjarni Sæmundsson collected animals from the sediments, and this is where they came across the famous Hafrún. The researchers took note of this particular clam because of its size, and he was later sent to a laboratory for tests. During testing, researchers counted the annual growth lines on the shell and could determine that he was 405 years old. This is not an exact way to determine age, especially when it is so high, but it still gave a rough estimate.

The 400 years old animal got a lot of attention in the media once the research papers were published, and it quickly got the nickname Ming because it was believed to have been alive during the Ming dynasty that lasted from 1368 to 1644. The researchers preferred the name Hafrún instead, which could roughly be translated from Icelandic to mean "the mystery of the ocean" (according to Wikipedia, so not a great source). Anyway, if you read the title, then you might have wondered why I first wrote 507 years, then later 405 years. I do have a good reason, because the researchers later decided to do another study to find the age of the clam, but this time they used carbon-14 dating. This method is a lot more expensive, but on the other hand, it gives a much better result as long as it's within the ranges where we still have enough C14 in the sample. The carbon-14 dating determined Hafrún to be 507 years old when he died at the hands of the researchers in 2006, with an error margin of only 2 years. This means the Hafrún was over half a century old when he died, making it the oldest animal that has ever been sampled. This puts the expected birth year of Hafrún to be in the year 1499! This means that Hafrún barely experienced the last year of the Middle Ages, and was a young clam when Leonardo da Vinci painted the Mona Lisa in 1503. It's pretty crazy to think of how long this clam lived before he was opened (and therefore killed) by researchers who studied benthic animals off the coast of Iceland.