Sea cucumbers protect coral reefs from disease and death

Once vibrant and sprawling, coral reefs are now shrinking at an alarming pace. Imagine an entire state like Georgia losing all of its trees in just a few decades – that’s the devastating speed at which coral reefs are vanishing.

However, a recent discovery by leading scientist Mark Hay and his colleague Cody Clements from Georgia Institute of Technology offers a glimmer of hope. The experts have identified an unexpected, yet crucial factor in the health and survival of coral reefs: sea cucumbers.

Underwater rainforests

Coral reefs, also known as underwater rainforests, support a vast array of marine creatures and shield coastlines from storms and erosion. However, these vital resources are declining due to climate change, pollution, and overfishing. Experts emphasize the need for their conservation. 

“It’s like if all the pine trees in Georgia disappeared over a period of 30 to 40 years,” said Hay. “Just imagine how that affects biodiversity and ecosystems of the ocean.”

Coral reefs and sea cucumbers

While often overlooked, sea cucumbers play a crucial role in keeping coral reefs healthy and stable. These creatures, resembling soft, leathery cucumbers, are found on the ocean floor all over the world. 

Sea cucumbers belong to the same group as starfish and sea urchins, known as echinoderms. Their primary function is to break down debris and recycle nutrients, a critical process for maintaining healthy and balanced marine ecosystems. 

Removal of sea cucumbers

The scientists conducted a unique experiment in French Polynesia and Palmyra Atoll. They carefully removed sea cucumbers from specific areas of the reef, while leaving other areas untouched. This allowed the team to directly compare the health of corals with and without the presence of sea cucumbers. 

By studying the consequences of removing these creatures, the researchers gained insights into their role in protecting corals from disease and death. The experiment was designed to closely resemble natural conditions, ensuring that the results accurately reflect the true impact of sea cucumbers on coral reef health. 

The study revealed the important, but often underestimated, role sea cucumbers play in protecting coral reefs from disease.

Decrease in coral reefs

The experts found that coral reefs where sea cucumbers have been removed experience much higher rates of coral disease and death. 

Sea cucumbers play a vital role in keeping the sand and soil around coral reefs clean. They act like natural vacuum cleaners, eating bits of dead plants and animal waste that sink to the bottom. This constant cleaning helps prevent the buildup of harmful bacteria and other substances that could harm the coral. 

The study shows that by removing these potentially harmful materials, sea cucumbers help create a healthier environment for the coral to thrive, making them less likely to get sick.

Recycling nutrients

Sea cucumbers aren’t just reef janitors; they’re crucial for keeping the entire ecosystem healthy. They act like recyclers by eating dead plants and animals on the seafloor. Inside their bodies, these materials are broken down and transformed into essential nutrients. These nutrients are then released back into the water, functioning like fertilizer for the diverse creatures living in the reef.

Without sea cucumbers, the reef faces a double threat. First, the absence of their cleaning action allows organic matter to accumulate, leading to the growth of harmful bacteria and substances that can damage the corals. Second, the missing link in the nutrient cycle creates an imbalance. 

Without sea cucumbers converting organic matter into usable nutrients, the reef loses its nutritional foundation, impacting the overall well-being and diversity of life in the ecosystem. This can affect not only the corals themselves, but everything that depends on them for survival.

“If you remove all the scum suckers in the great fish tank of Earth, you’re going to get a dirty tank eventually,” said Clements. “People have paid lip service to the idea that sea cucumbers could be important for a long time, but we didn’t know the scale of their importance until now.”

Threat of extinction 

The study reveals a worrying issue: sea cucumber populations, once plentiful in many regions, are now decreasing rapidly due to being caught in large numbers. 

The high demand for sea cucumbers in certain foods and traditional medicine has led to a significant drop in their numbers. Sea cucumbers are a crucial food source for many marine animals, and their disappearance would cause a ripple effect throughout the food chain, potentially leading to population decline in other species. This would ultimately reduce the variety of life in the ocean (biodiversity).

Sea cucumber conservation 

Sea cucumbers are crucial to healthy oceans, but they face threats from overharvesting.  “If we don’t cut back on pollution, if we don’t cut back on overharvesting, and if we don’t cut back on global warming, there isn’t much hope. It’s a challenge, but you can either give up and go home, or you can keep working on it,” said Dr. Clements. 

To ensure their survival and protect marine ecosystems, we need to take several steps. We must regulate how many sea cucumbers can be caught to prevent overfishing. 

In addition, the creation of marine protected areas would establish specific areas of the ocean where sea cucumbers could thrive without being disturbed. Furthermore, adopting sustainable trade practices – which prioritize responsible harvesting and consumption – is essential. 

The study is published in the journal Nature Communications.

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