The Red Sea, a haven for marine biodiversity, is facing an ecological challenge as black sea urchins suffer a mysterious decline due to a waterborne parasite. The Red Sea’s coral reefs have shown resilience to climate change, particularly warming sea temperatures. However, the decline in key species, such as sea urchins, raises concerns about the future health of these living reefs. These reefs are estimated to be over 5,000 years old.

The decline of black sea urchins was first noticed near the city of Eilat in Israel. These sea urchins, known for their formidable defensive spines, once covered parts of the coastal reefs. However, new surveys indicate a 90% reduction in their population in the Jordanian resort of Aqaba, with similar mass disappearances observed in Egypt and Saudi Arabia.

The species scientifically known as Diadema antillarum encountered the same circumstances in 1983-84. Approximately 98% of these sea urchins faced mysterious deaths. During that period, their protective needles, which shielded their bodies, suddenly fell off, rendering them vulnerable to predators in their surroundings.

The cause of the decline is a waterborne parasite that causes rapid sea urchin mortality. Dr Omri Bronstein, attached to Tel Aviv University, has observed visible signs of the disease, including paralysis of the sea urchin’s spines and feet, ultimately leading to necrosis and leaving behind bare skeletons.

The consequences of this decline are far-reaching, threatening the Red Sea’s coral reefs. With the loss of sea urchins, there is a risk of fast-growing green algae, which could outcompete corals for space and sunlight. This, in turn, could jeopardise the delicate balance of the underwater paradise and significantly impact tourism in the region.

Videos filmed by scuba divers reveal the plight of infected black sea urchins. The spread of the disease is likely facilitated by fish and human activities, including shipping.

Sea urchins play a crucial role in the ecosystem by assisting coral larvae to settle and grow. They consume algae to prevent overgrowth. Without sea urchins, unchecked algae growth could stifle coral growth, leading to algae-dominated fields.

Marine biologist Dr Mahmoud Hanafy has conducted studies along the Egyptian Red Sea coast and observed a significant decline in black sea urchins from north of Hurghada to the south of Marsa Alam, suggesting a potential disappearance of the species across the region.

A similar situation has been observed in Jordan and Saudi Arabia, raising concerns about the possible spread of the trend to neighbouring regions, including the Arabian Gulf.

Experts differ regarding the potential consequences of sea urchin decline. Some scientists in Egypt and Jordan believe that their reefs are not yet showing significant negative impacts. However, other experts fear a situation similar to that in the Caribbean 40 years ago. In this case, a similar pathogen led to the near-extinction of a closely related species of sea urchin, resulting in algae dominance over coral reefs.

During winter, when algae bloom naturally, the effects of sea urchin decline in the Red Sea may become more apparent. This period will require close monitoring to assess the potential ecological consequences of sea urchin population loss.