An Ocean Quahog Shows Its Age Like Rings on a Tree

The ocean quahog is a bivalve mollusk, meaning it has two hard shells connected by a hinge. The shell is thick and oval-shaped, with a smooth surface often dark brown or black on the outside and white on the inside.

Growth increments in the shell of the bivalve Arctica islandica form annual rings, also known as growth lines — similar to those in trees — which scientists use to determine the clam's age.

This species is relatively small compared to its lifespan, typically measuring 2 to 4 inches (5 to 10 cm) across, although larger specimens have been found. Its sturdy shell helps it burrow into the sediment and protects it from predators.

While Arctica islandica is the primary species, populations exhibit regional variations depending on their environment. Ocean quahogs endemic to the North Icelandic Shelf, for example, display specific growth patterns influenced by the cold temperature and the nutrient-rich waters of that region.

Although there are no formally recognized subspecies, research by scientists like Paul Butler (the 2013 findings by Butler et al. was when the age record was set) has highlighted differences in growth rates and longevity among populations, offering clues about marine climate on the North Atlantic and its impact on the species [source: ScienceNordic.com].

Some other informal names for Arctica islandica include mahogany clam, mahogany quahog and black clam.

Ocean quahogs are solitary creatures that live buried in the ocean floor. Unlike some other bivalves, they do not form large, interconnected colonies. However, they often share their habitat with other benthic (seafloor-dwelling) organisms.

Though they don't interact socially, ocean quahogs play an important role in their ecosystem by filtering water and serving as prey for species like starfish and crabs.

Ocean quahogs are filter feeders, drawing water into their shells and extracting tiny particles of plankton and organic material from the sea. This feeding method keeps the surrounding waters clean while providing the quahogs with the nutrients they need to survive.

Despite their slow metabolism, ocean quahogs are efficient feeders. This trait, along with their low energy requirements, contributes to their status as the longest-lived bivalve species.

Ocean quahogs thrive in cold, nutrient-rich waters, particularly in the North Atlantic. They are commonly found at depths of 80 to 500 feet (24 to 152 meters), where they burrow into sandy or muddy sediments on the seafloor.

The North Icelandic Shelf is a key habitat for this species, with a stable marine climate that supports their slow growth and longevity.

The climate on the North Atlantic plays a crucial role in the quahogs' growth increments, which scientists study to understand historical changes in marine conditions. These clams serve as natural archives, recording shifts in temperature and ecosystem health over centuries.

The life cycle of the ocean quahog begins as a free-swimming larva, which eventually settles onto the seafloor and burrows into the sediment.

Once it progresses through its sexual maturity stages, the quahog becomes sedentary, spending the rest of its life in a single location. Ocean quahogs grow very slowly, adding thin layers to their shells each year.

This bivalve is incredibly long-lived. The oldest recorded specimen was over 500 years old at the time of its harvest.

Scientists don't know the upper age limit for the long-lived species, and research into what they can teach us about longevity is ongoing. Their slow growth and ability to conserve energy help them endure challenging environmental conditions, making them one of the most resilient marine animals.

The ocean quahog isn't just a marvel of nature, it is a significant crop in the fisheries where it is a native species. The 2022 haul produced 15 million pounds of meat, worth $12 million. That's a lot of clam chowder! In fact, it's very likely that the clam in your your soup is an ocean quahog/clam.

The ocean quahog is known as a pretty sustainable food source, managed by the NOAA (National Oceanic and Atmospheric Administration) with considerable success over the past several decades.

There are strict rules about how many can be harvested in a year, how old they have to be and the specific tools that are used to harvest them.

Ocean quahogs are not currently classified as endangered, but they face threats from commercial fishing and climate change. Commercial clam dredges can disrupt their habitats, while warming ocean temperatures may impact their growth and reproduction.

Scientists continue to monitor ocean quahog populations to ensure sustainable harvesting and to use their shells as valuable records of marine climate history. Protecting this long-lived bivalve is essential for maintaining the health of its ecosystem and understanding our changing oceans.

We created this article in conjunction with AI technology, then make sure it was fact-checked and edited by a HowStuffWorks editor.