Shellfish for Dinner: More than just Clams and Oysters

Two clams, a mussel, an oyster, on a bed of algae
Four bivalves found along the Maine coast presented together in a bed of seaweed at low tide. Clockwise from the top right is a Northern quahog (Mercenaria mercenaria), an oyster (Crassostrea virginica), a steamer clam (Mya arenaria) and a blue mussel (Mytilus edulis) (Smithsonian Institution)

Shellfish are favorite summertime staples when it comes to a meal. Shucked raw, steamed in broth, baked, or stuffed, they are sure to complete a trip to the beach or coast. Shellfish are also a staple in many coastal diets, supplying a necessary and reliable source of protein and essential minerals to people across the globe. It turns out that favorites like oysters, clams, and mussels, aren’t the only shellfish sought after for food. The Food and Agriculture Organization monitors fishery data for roughly 80 popular bivalves, shellfish with two clasping shells, but new research by Smithsonian researcher Stewart Edie and University of Birmingham colleague Shan Huang scoured the scientific literature and found mention of an additional 720 species targeted for food.  

They found that big species are easy targets and are the most sought-after bivalves for food. This was as expected—species that are big, live in shallow water, and are found across large geographic areas are the most popular species to harvest because they are easy to find and have more meat. And, for the most part this rang true. But surprisingly, the researchers found that people get creative and inventive when it comes to harvesting some shellfish that inhabit less obvious locations.   

Preview a cornucopia of shellfish
Human-harvested shellfish from the Smithsonian’s National Museum of Natural History Research Collections. (Smithsonian Institution)

The piddock clams (Pholadidae, aka Angel Wing Clams) have adapted an ingenious way of avoiding predators. After suctioning onto a rock, the clams rotate the sharp ridges along the butt end of their shell like a drill bit until they’ve bored a small hole to hideaway inside the rock. Records dating back to ancient Rome indicate that they are also sought after for food. With an axe or a sledgehammer, clam foragers can remove the clams from their hideouts, though the habitat where they bore is ultimately destroyed. Along the Oregon coast in the early 1900s the piddock clams were known as “rock oysters” and highly sought after. President William Howard Taft was even served a meal featuring piddock clams during his trip to the West Coast. But by the 1940s the rocky environment where the clams like to burrow was mostly destroyed by clammers and the piddock clams mostly disappeared from dinner tables. 

Another surprise was finding lucinid clams (Lucinidae) among bivalves that people harvest for food. While most bivalves obtain nutrients by filter feeding algae from the ocean water, lucinids live in sulfur rich mudflats and house chemosymbiotic bacteria within the tissue of their gills. These bacteria use hydrogen sulfide and oxygen from the environment to produce nutrients for their host clams, meaning when humans consume lucinids, they are obtaining nutrients that began as sulfur in the harbor mud. In Tonga, women collect the lucina clams (known locally as Tu’ulalo) from the mudflats and cook them in special dishes for feasts.   

Understanding which bivalves are targeted for human consumption is more than fulfilling a simple curiosity. Knowing which bivalves are being harvested can help predict whether they are at risk for overharvesting, especially in a world rapidly changing due to climate change. The Long Island Sound by New York City was once the global center for oyster harvesting and consumption, but overharvesting and environmental conditions led to the oyster population’s collapse in the late 1800s. 

Preview a hole with a pile of clams and a shovel at a muddy beach
At low tide muddy beaches and mudflats are a great place to harvest shellfish. (Smithsonian Institution)

Luckily, many of the character traits that make bivalves attractive for harvesting also protect bivalves from extinction. “We’re fortunate that the species we eat also tend to be more resistant to extinction,” said Edie. “But humans can transform the environment in the geologic blink of an eye, and we have to sustainably manage these species so they are available for generations that will come after us.”  

An assessment of bivalves throughout the fossil record shows that bivalves that are large-bodied, have a high tolerance for temperature changes, and have broad geographic ranges are the least vulnerable to extinction. This makes sense. Large-bodied bivalves tend to have higher fecundity, or “fertility,” and produce more offspring so they can easily replenish populations in the event of disturbances, like a natural disaster. Shallow-water species that experience daily temperature shifts due to the ebb and flow of the tides may also be well suited for longer-term temperature shifts due to heat waves or cold snaps, or even climate change. In the event of localized tragedies that wipe out an area’s population, those species will continue to live in other unaffected regions. 

As the world’s population continues to grow and the world’s climate continues to change, understanding which bivalve species are the most susceptible to overharvesting will be key to keeping healthy and productive ecosystems for future generations. Through this research we now know that not only is the eastern Atlantic coast of western Africa a hotspot to monitor, but the southeast Pacific is of special concern for management and conservation. The vast majority of the newly found species come from the Pacific Ocean and Indian Ocean, indicating there is still much to learn about bivalve harvesting across the globe.

August 2023