TAU meta-analysis finds pathogens, storms, and extreme temperatures are the leading causes of sea urchin mass mortality events.

Two pioneering studies by researchers from the School of Zoology and the Steinhardt Museum of Natural History at Tel Aviv University, led by Dr. Omri Bronstein, have identified the primary drivers of sea urchin mass mortality events over recent decades: pathogens, storms, and extreme temperatures. In addition, Dr. Bronstein and his team have developed an innovative method for genetic sampling in marine environments – using a swab similar to a COVID-19 test — to enable rapid and non-invasive monitoring of marine animals and underwater disease outbreaks.

The first study, published in the journal Biological Reviews, presents a meta-analysis of all 110 scientifically documented mass mortality events (MMEs) among sea urchins recorded between 1888 and 2024. Dr. Bronstein and PhD student Lisa Schmidt conducted a comprehensive review of the history of these events, showing that most reported MMEs originate in the Northern Hemisphere — particularly in the United States, Western Europe, and Japan — where the majority of research and funding are concentrated. The Tel Aviv University researchers classified five main causes of these events and found that 33% were caused by pathogens, 25% by catastrophic events such as storms and oxygen depletion, 24% by extreme temperatures, 11% by algal blooms, and 7% by human activity, such as pollution and habitat destruction.

Left to right: Mai Bonomo & Dr. Omri Bronstein holding sea urchin and sample tube

“This is a meta-analysis of all scientific literature on the subject,” says Dr. Bronstein. “For each mass mortality event, we mapped where and when it occurred, which species were affected, and most importantly — what the causes were. After filtering out hundreds of publications who lacked sufficient credible data to be included in our analyses, ee found that pathogens are the leading cause of mass mortalities among sea urchins. This finding aligns closely with what we are seeing today in the modern wave of die-offs — from the Caribbean to the Red Sea and the Indian Ocean. There is a tendency to attribute everything to global warming, but that is not always accurate. In many cases, mortality is not directly related to heat, as some affected sea urchin species naturally live in even warmer environments. These temperatures may not be optimal, but they are not lethal for these species. The problem is that warming influences many other environmental factors, which can combine into a deadly mix. For example, warmer waters tend to have lower dissolved oxygen and higher pathogen activity.”

A Global Sea Urchin Pandemic

In 2023, Dr. Bronstein identified a mass mortality event of long-spined sea urchins (Diadema setosum) along the Red Sea coast. He subsequently found that the same pathogen — a ciliate parasite — responsible for wiping out a related Caribbean species was also to blame. Since that discovery, the outbreak has spread to the Indian Ocean, reappeared in the Caribbean, and is now considered a global pandemic threatening sea urchin populations worldwide.

“Sea urchins are vital to coral reef health,” explains Dr. Bronstein. “They are the ‘gardeners’ of the reef: they feed on algae and prevent it from overgrowing and suffocating the corals competing for sunlight. In 1983, the most dominant Caribbean sea urchin species, Diadema antillarum, died in vast numbers from an unknown reason at the time; algae proliferated uncontrollably, shaded the corals, and the entire ecosystem shifted from coral reefs to algal fields. Even 40 years later, the sea urchin population — and the reefs — have not recovered. We fear that the same process may now occur in other parts of the world where mass die-offs are happening, mainly among the long-spined sea urchin, a relative of the Caribbean species — the black urchin with long spines familiar to everyone. Until recently, it was one of the most common reef urchins in Eilat; today it has almost disappeared from large parts of the Red Sea. This is a very violent event: within less than 48 hours, a healthy population turns into disintegrating skeletons. In some sites in Eilat and Sinai, mortality reached 100%. Later, mass deaths were recorded on Réunion Island in the Indian Ocean, and we are now investigating three additional mass mortality events in the Atlantic and Indian Ocean, and even the Mediterranean Seas. What began as a local mortality event has become regional and then global, posing a threat to coral reefs everywhere.”

Close-up of hand swabbing sea urchin underwater tank

The Challenge of Genetic Sampling Underwater

To address one of the major challenges in marine genetic sampling, graduate student Mai Bonomo and Dr. Bronstein published a separate study in Molecular Ecology Resources, developing a new, inexpensive, and non-invasive method for collecting underwater genetic samples at scale.

“The main tools used today to identify both animals and pathogens are genetic,” says Dr. Bronstein. “But molecular ecology faces a fundamental problem: there’s no simple way to sample DNA from live marine animals underwater. As a result, many studies rely on invasive methods that harm the animal or even require sacrificing it completely to bring it into the lab. Therefore, research in this field is heavily regulated, weighing each case’s scientific value against environmental ethics. For example, sampling is prohibited in marine nature reserves, there are restrictions and bans on shipping samples abroad — including corals — and every scientific publication must present the official permits for each sample it reports. Our need to overcome this bottleneck arose from the sea urchin pandemic. Today, there are only two ways to detect diseased urchins: visually — which is too late, as the animals are already dying — or through genetic tools that can detect disease before symptoms appear. But if detecting disease requires removing the animal from the sea, it makes no difference whether it’s sick or not — we end up sacrificing it.”

A Simple New Tool for Rapid, Non-Invasive Sampling

To overcome this challenge, Tel Aviv University researchers developed a specialized underwater genetic sampling kit that is durable, reliable, inexpensive, and easy to use — and it is already being adopted by research groups worldwide, especially in remote or sensitive areas.

“We developed a new tool for underwater DNA sampling that resembles a COVID-19 test,” explains Dr. Bronstein. “At the end of a special tube filled with a preservation liquid is a membrane preventing water penetration, sealed with a clip-cap — much like some toothpaste tubes. Just like a COVID test, the researcher gently swabs the surface of the marine animal, without harming or moving it. There’s no need to collect mucus as in humans — just a light swipe is enough. The swab is then inserted into the tube, piercing the membrane that protects the preservation liquid inside, and the cap is locked to secure the sample. That’s it. A single researcher can collect dozens of samples in one dive, under almost any environmental or depth conditions.

The kit has already been tested in challenging environments, including field expeditions to Djibouti and Réunion Island, and the results are very promising: samples remained exceptionally well-preserved for months without refrigeration before arriving at our lab, and still allowed for sensitive genetic analyses. In a large-scale trial we conducted in the Gulf of Eilat, we collected genetic material from hundreds of echinoderms — the group that includes sea urchins and starfish — within just a few months, and performed the most extensive genetic analysis ever conducted on these species in the region. This led to the discovery of several new species and the reclassification of others previously unknown to science. This is a simple and elegant solution to one of the most persistent technical challenges in marine molecular ecology.”