Marine Pandemics Are Becoming a Growing Threat to Our Seas

A deadly pathogen is wiping out sea urchins, spreading across oceans, and threatening the balance of coral reef ecosystems

I was fortunate to do my bachelor’s degree in Barcelona, near the Mediterranean coast. 

As you can imagine, many of our classes used the sea as a lab. Taking samples, measuring variables, and surveying biodiversity. Among all creatures, sea urchins have always fascinated me. Not just because of their unique shapes and forms, or the way they reproduce or transport nutrients, but because of their ecological role. 

Today’s story tells us more about why these creatures are so important for the health of our oceans while exploring a lethal pathogen attacking them. 

Coral reefs are often called the rainforests of the sea for their exuberant biodiversity, providing essential shelter for fish, crabs, and countless other marine creatures. 

But beneath the waves and the shiny colors, an ecological disaster is unfolding. Although it might not grab headlines like wildfires or oil spills, it could have equally devastating consequences. A deadly disease is sweeping through sea urchin populations, and the effects are already rippling across the ocean.

A recent study led by an international team of researchers and published in Ecology has confirmed one of the culprits: a microscopic parasite wiping out sea urchins at an alarming rate. First seen in the Caribbean in 1983, this pathogen has now jumped oceans, reaching the Red Sea and, most recently, the Indian Ocean. 

But what makes this so concerning? Why should we care about sea urchins?

Well, sea urchins play a critical role in keeping coral reefs healthy, much like lawnmowers in a garden — without them, algae can run wild, choking out coral and reshaping entire ecosystems. They are the gardeners of the ocean. 

Tracking a Marine Pandemic

To get to the bottom of this crisis, researchers did forensic detective work, but underwater. Using genetic tools, they traced the disease from the Caribbean to the Red Sea and now to Réunion Island, East of Madagascar, in the Indian Ocean. 

The pathogen, a tiny ciliate from the Philaster genus, spreads through water, infecting sea urchins and causing them to lose their spines and disintegrate within days. The study combined genetic analysis, field surveys, and historical data to confirm that the same disease is behind these die-offs in all these seas and oceans.

We need to understand that this isn’t a slow, creeping problem — it’s a full-blown catastrophe in some areas. In the Red Sea, for example, mortality rates hit nearly 100% in certain locations, wiping out entire populations of Diadema sea urchins within 48 hours. Forty-eight hours. 

That’s the ecological equivalent of an entire forest vanishing in two days. And now, with the pathogen confirmed in the Indian Ocean, researchers worry it could continue its spread, possibly reaching the Pacific.

Why This Matters 

As we mentioned above, losing sea urchins isn’t just about one species disappearing. In the 1980s, when a similar die-off happened in the Caribbean, reefs quickly shifted from coral-covered landscapes to algae-dominated ones. 

Algae, left unchecked, smother corals by blocking sunlight and outcompeting them for space. Forty years later, many Caribbean reefs have yet to recover.

Trust me, we have a saltwater aquarium at home, and whenever algae take over, we see a dramatic coral die-off. 

Think of a coral reef as a city with different creatures playing different roles — some are architects (coral builders), some are scavengers (fish that clean up debris), and some, like sea urchins, are maintenance workers keeping the algae from taking over. Remove one of these key players, and the whole system starts to fall apart.

Dr. Omri Bronstein perfectly highlights the scale of the problem: “This is a first-rate ecological disaster.” He’s not exaggerating. Coral reefs already face massive threats from climate change, pollution, and overfishing. Losing sea urchins adds another stressor, one that could push struggling reefs past yet another tipping point.

How Did This Happen?

I know what you’re thinking. How did this disease spread from one ocean to another when there’s land in between?

There are two main theories about how the pathogen spread so fast. One possibility is that it hitched a ride in ballast water. Cargo ships take in seawater for balance when they’re empty and release it when they load cargo, unintentionally moving tiny marine organisms across oceans.

If true, this means major shipping routes may have unknowingly carried the disease from the Caribbean to the Red Sea and beyond. In fact, researchers recently found sea urchin die-offs in West Africa, precisely where cargo ships from the Caribbean often stop.

The second theory is more concerning: the pathogen may have always been present, but changes in ocean conditions — such as warming waters or pollution — could have triggered its virulence. 

If this is the case, the problem isn’t just about movement; it’s about an environmental shift making diseases more dangerous. And while this sounds scary, this wouldn’t be the first time climate change has amplified marine diseases. Warmer waters are known to stress corals, fish, and other organisms, making them more vulnerable to infections. And that’s what pathogens love most.

What Can Be Done?

Unfortunately, there’s no underwater vaccine for sea urchins. Once the pathogen is in a population, there’s little that can be done to stop it. This is why researchers are now focusing on two key areas: tracking its spread and preserving healthy populations for future recovery.

For example, at the Israel Aquarium in Jerusalem, scientists have set up a breeding program to raise unaffected sea urchins in a controlled environment, hoping to one day reintroduce them to devastated reefs. It’s a bit like the conservation efforts for endangered land animals — except instead of pandas or rhinos, these conservationists are working with spiny, algae-eating invertebrates. 

The team is also developing genetic tests to detect the pathogen early, much like a COVID test for sea urchins, in an effort to prevent future outbreaks.

However, the big question is whether reefs can recover before it’s too late. In places like the Caribbean, where sea urchin populations never fully bounced back, the outlook isn’t promising. But in other regions, proactive conservation measures could make a difference — if it happens in time.

A Wake-Up Call for Ocean Health

While this might seem like a regional issue, it’s a warning sign for the bigger picture. Marine ecosystems are complex, and when one piece is removed, the consequences can cascade through the entire system. 

The fact that this disease is spreading so rapidly across oceans suggests that human activity — whether through shipping, climate change, or pollution — is playing a role.

We nee to remember that protecting coral reefs isn’t just about saving pretty fish and colorful corals; these ecosystems provide food, coastal protection, and economic support for millions of people worldwide. 

If a tiny parasite can trigger such massive consequences, it’s a reminder of how interconnected everything is. Scientists are racing against the clock to understand and mitigate this crisis, but the best long-term solution is tackling the root causes: keeping our oceans healthier, reducing stressors on marine life, and preventing the next ecological disaster before it starts.

Science will provide the answers and tools if we make it work. 

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Best,

Sílvia P-M, PhD Climate Ages

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