BY: PHILIPPE DE JOCAS
What’s the lifespan of the longest-living animal? Humans can live for over a hundred years if we receive adequate care. Other mammals, such as the bowhead whale, can live for two hundred years; reptiles like the Galapagos giant tortoise and the tuatara can match that stat.
It’s easy to overlook the creature who actually wins this competition; it’s more likely that you’ll see one served up at a seafood restaurant than at an awards ceremony celebrating its longevity. The hard clam, also known as the quahog clam, is a small, unprepossessing bivalve that grows in great clumpy clusters all across the North Atlantic Ocean.
The frigid, icy waters that it inhabits slow metabolic activity to a crawl. Other animals that inhabit this environment grow slowly and live sluggishly, but hard clams have them all outmatched. Scientists aren’t sure just how long hard clams live for; the oldest known specimen, a tiny clam named Ming, was estimated at 507 years old. It’s entirely possible that some of its neighbours might be even older. Like many animals, clams add “growth rings” to their shells as they grow; a similar phenomenon exists in trees and even in human bones and teeth. Scientists can count the number of rings and determine a clam’s age.
These diminutive senior citizens are generally considered novelties at best, and hors d‘oeuvres at worst. But as climate change intensifies, scientists have developed a newfound appreciation for these humble lifeforms, which may prove useful as markers tracking the historical effects of climate change. Scientists at the Welsh Cardiff and Bangor Universities have reached a breakthrough in determining the significance of these growth rings. The chemical layers that the clam uses in the development of growth rings act as proxies for the chemical makeup of the surrounding waters. Trace minerals in the surrounding water – which may come from surface runoff, volcanic eruptions, or changing currents – affect the quality and thickness of a clam’s growth rings. Clams are like tiny clocks, and hard clams can keep track of centuries. From samples of clam communities, scientists have reconstructed a history of changing oceanic climates that spans back for more than 1,000 years.
The North Atlantic Ocean seems as though it’s far away from the most concentrated hubs of climate change activity, but this stretch of ocean provides several key insights into our changing climate. Prior to 1800 – the rise of the industrial era, and the time period when global warming truly began – changes in the North Atlantic began when a series of minor volcanic eruptions altered the ocean climate. Ancient rings show that at one point, solar activity was the premier factor in ocean climatology. Nowadays, however, changes in the North Atlantic lag behind atmospheric conditions, a crucial change that many scientists attribute to global warming. Greenhouse gasses, not solar activity, may prove to be the next major factor in predicting future climate trends.
Clams, oysters, mussels, and other humble rock-clingers – for all their seeming humility – have become canaries in the proverbial coal mine. Thanks to their warnings, tracking the complicated causes and effects of climate change has become less of a guessing game.