Picture four million tonnes of clams. That's how many Manila clams the world harvested in 2020. Worth over seven billion euros.

Now picture those farms empty.

The Manila clam, a mollusk with the scientific name Ruditapes philippinarum, accounts for nearly a quarter of all farmed shellfish globally. It thrives in shallow coastal waters across Asia, Europe, and North America. Farmers cultivate it. Consumers demand it. Economies depend on it.

But the water is changing.

A new study uses climate projection models to map where Manila clams can survive by the year 2100. The results reveal a world reshaped by warming seas and shifting salinity. Some coastlines will become havens. Others will turn hostile.

The research focused on two environmental drivers: sea surface temperature and salinity. These variables determine whether clams can feed, reproduce, and survive. Using data from thousands of locations where clams currently live, scientists built a habitat suitability model. They tested it against present conditions. Then they ran it forward to 2100 under a high-emissions climate scenario known as RCP 8.5.

What they found was striking.

The Temperature Threshold

Manila clams tolerate a range of conditions, but they have limits. The model identified fifteen degrees Celsius as optimal. Below eight degrees, survival probability drops below fifty percent. Above twenty-two degrees, the same collapse occurs.

This sensitivity matters because ocean temperatures are rising unevenly. Some regions warm faster than others. The North Atlantic and Southern Ocean are developing hotspots where warming accelerates beyond the global average.

Salinity adds another layer of complexity. Clams perform best in salinities between twenty and twenty-five parts per thousand. When salinity drops below fourteen, clams experience oxidative stress. Extended exposure kills them. When salinity exceeds thirty-five, their likelihood of survival again plummets.

These aren't abstract numbers. They're survival thresholds.

The model predicted habitat suitability with good accuracy, achieving an AUC score of 0.88. AUC, or area under the receiver operating curve, measures how well a model distinguishes suitable from unsuitable habitat. A score above 0.8 is considered strong.

Winners and Losers

By 2100, northern Europe and Alaska emerge as big winners. Coastlines that are currently too cold become habitable. Norway's shores gain suitability. So does Alaska's entire coastline, where probability of occurrence jumps from zero to one hundred percent.

Canada's west coast maintains high suitability. So does southern Scandinavia and the Netherlands.

But the Mediterranean tells a different story.

Italy, which produced ninety-two percent of Europe's farmed Manila clams in 2021, faces a habitat collapse. Suitability around Italian coastlines drops by more than fifty percent. Greece's eastern coast follows the same trajectory. Water temperatures climb beyond the clams' tolerance.

Production there, measured in thousands of tonnes and millions of euros, could vanish.

Asia presents a divided future. Below twenty degrees north latitude, suitability increases. Indonesia, Malaysia, Thailand, and Myanmar all see their coastal waters become more hospitable. Above forty degrees north, suitability also rises. Hokkaido, Japan's northernmost island, and Russia's Pacific coast both gain.

But between those latitudes? Disaster.

China's central coastline, where over two million tonnes are currently farmed each year, loses suitability dramatically. The model predicts a fifty percent decline. China produces ninety-six percent of the world's Manila clams. That's not a regional problem. It's a global food security issue.

Why This Matters

Aquaculture supplied fifty-six percent of aquatic food for human consumption in 2020. Marine shellfish make up over half of the seventy-three most important global aquaculture species. They're not a luxury. They're infrastructure.

The Manila clam also provides ecosystem services. It filters water, removing nitrogen and phosphorus. This reduces eutrophication, the process where excess nutrients choke aquatic life. Clams stabilize benthic communities, the organisms living on or near the seafloor. Their presence or absence ripples through entire ecosystems.

When habitat suitability declines, these services decline with it. Food production suffers. Water quality degrades. Communities that depend on clam farming lose livelihoods.

The study also identified potential refuges. Seagrass beds, for instance, can buffer temperature extremes during marine heatwaves. Clams in seagrass habitats experience less thermal stress than those in open sediment. Reduced stocking density might also help, giving individual clams more resources to cope with stress.

But these are short-term fixes. They don't address the fundamental problem: the ocean is changing faster than clams can adapt.

What Comes Next

Climate models always carry uncertainty. This study used relatively coarse resolution data, with grid cells roughly nine kilometers across. Finer-scale models might reveal local microclimates where clams can persist. The analysis also focused on temperature and salinity alone. Other variables like dissolved oxygen and pH could refine predictions further.

The model itself performed well under cross-validation but wasn't tested against fully independent data. That's a common limitation. Future work should validate predictions using new observations from different regions.

Still, the core finding remains robust. Where water warms beyond twenty-two degrees and stays there, Manila clams struggle. Where it warms to fifteen degrees from colder baselines, they thrive.

This creates opportunities. Norway, Alaska, and Indonesia could expand production. Investment in aquaculture infrastructure in these regions might offset losses elsewhere. Economic growth. Sustainable food production. Jobs.

But it also demands action in places facing decline. China and Italy produce vast quantities of clams today. Without adaptation strategies, their industries could collapse. That means economic loss, food insecurity, and ecosystem disruption.

Adaptive management could help. Farmers might shift operations northward within their countries. They might invest in cooling systems or selective breeding for heat tolerance. Policymakers might protect seagrass habitats or regulate stocking densities.

None of these solutions are simple. All of them cost money. And all of them require decisions made now for a world decades away.

The Bigger Picture

Manila clams don't migrate like fish. They're bivalves. They settle as larvae and stay put. If their habitat becomes unsuitable, they die. Populations don't shift; they collapse.

The study maps this collapse and expansion across the globe. It identifies where risk concentrates and where opportunity emerges. That knowledge matters for farmers, policymakers, and anyone who eats seafood.

Because four million tonnes of clams isn't just a number. It's food security. It's livelihoods. It's ecosystems functioning or failing.

And by 2100, the map will look very different.

Credit & Disclaimer: This article is a popular science summary written to make peer-reviewed research accessible to a broad audience. All scientific facts, findings, and conclusions presented here are drawn directly and accurately from the original research paper. Readers are strongly encouraged to consult the full research article for complete data, methodologies, and scientific detail. The article can be accessed through https://doi.org/10.1016/j.ecss.2025.109307