Gozo’s Long-Spined Sea Urchins

Diadema antillarum

Gozo has a small population of long-spiny sea urchins, which differ in size and appearance from its smaller relation, the Stony sea urchin (Rizza). You can characterise a Diadema antillarum by its exceptionally long black spines. It is a species of sea urchin belonging to the Family Diadematidae.

Distribution;

Often found on coral reefs in the western Atlantic and Caribbean basin. However, Gozo has a small, but healthy population found in crevices between rocks. The long-spiny sea urchin usually lives in 1 – 10 metres of water among corals and rocks.

Life habits:

Their long spines protrude from cracks and crevices where they stay throughout the daytime. Diadema is very sensitive to light. As a result, their resting place is often in the shade. However, they will live in more exposed areas if a suitable place is not to be found. Long-spiny sea urchins eat algae, sometimes seagrass. It is also known that starving sea urchins will become carnivorous when algae and seagrass are difficult to find.

Anatomy;

Diadematidae antillarum has a shell similar to most other sea urchins. Each individual will grow their spines to a standard length of 10 – 12 cm. However, some large individuals will grow spines up to 30 cm in length. The urchin is very active and possesses a high reactivity and sensitivity to light and water disturbances. The sea urchin will wave its spines in the direction of the upsetting occurrence. Once a disturbance occurs they retreat into their crevice or hole immediately, if need be.

Ecological Importance:

The Diadematidae antillarum is found in many tropical regions, even in the Mediterranean Sea. It plays an important role in the marine environment by consuming algae. If algae are left to its own devices, it will grow to such an extent that they smother coral reefs. Even in rocky areas and shallow coral reefs where marine life thrive. Long-spiny sea urchins live in holes between the rocks and graze on algae at night. They move around 1 metre from their crevice or hole in pursuit of algae to feed on at night.

Long-spiny sea urchins decline;

In the year 1983, throughout the Caribbean, South America and the Bahamas Diadematidae antillarum underwent mass mortality of more than 97%. This then led to some reefs and marine environments becoming overgrown by foliose macroalgae. Furthermore, it compounded into a great decline of scleractinian corals. As a result, quick-growing algae has an overall negative effect on coral reef resilience and its recovery.

Reef and Coral protectors;

Algae grow much faster than coral. It can take thousands of years for coral to grow only a few inches, whereas algae can take as little as a few days. Without long spiny urchins, algae would grow unchecked shading the delicate coral from the sun’s rays. This would eventually kill the coral that requires lots of sunlight in order to flourish and grow. The long-spiny sea urchin plays a massive role in the protection of coral reefs and the marine environment. We should not underestimate how vital they are and the impact this has on reefs when they die-off.

Predators;

Known predators are Toadfish, Caribbean Helmets, Caribbean spiny lobsters and Queen triggerfish. The spines of the Diadema antillarum are very brittle and break into fragments if wounded. Any human being unlucky enough to stand on a long-spiny sea urchin with bare feet will experience extreme difficulty in removing the spine fragments. Furthermore, the spines carry bacteria which causes infection, Their spines carry a mild poison to aid the deterrent of smaller predators, although the toxin has little effect on humans. The spines of sea urchin are capable of penetrating a wetsuit, skin, shoes or beach shoes.

Sea urchins will gather together in groups of 20 or more to provide protection against predators.

Reproduction and recovery;

High-powered storms, predators, humans and waves tend to slow the re-population of Diadematidae antillarum. They are often seen as a nuisance by divers who practice poor buoyancy control and beach-goers. Certain resorts and beach clubs remove them from the popular beach-resort bathing areas. High winds and storms wash the sea urchins out of the crevices and holes, leaving them exposed to perish.

To reproduce, both female and male urchins excrete fluid to alert other urchins to respond by releasing their eggs and sperm in mass production. There is no physical mating of individuals, both fertilisation and gestation occur in the open water. During the summer season, the sea urchins release eggs and sperm once during each lunar month. This procedure is dependent upon temperature, where northern and southern hemispheres may spawn at different times. It appears that spawning has a connection to the lunar calendar.

This method is very successful in highly dense populated areas, however, in low-density populations, it is often not enough to initiate the fertilisation procedure.

There is no parental involvement with the juveniles after spawning.

Life expectancy;

This varies and relates to certain factors such as food availability. Long-spiny sea urchins develop quicker in warmer climates, however, they tend to have a shorter life-span than those in colder climates. Their average lifespan status in the wild is 6 years. The typical wild lifespan is 4 to 8 years.

These creatures are vital to the health of our ocean and we should take care not to destroy them. Although they are a delicatessen in some countries, it is better to leave them where they belong – in the ocean!

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