Who?
Family: Echinodermata
Species: Diadema antillarum
Species ID: E.DA
Description: A relatively large urchin with long black spines (1) a spherical test, or “shell” (2), and a small mouth located underneath the body (3). Spines are serrated and very brittle, easily breaking off in skin if accidently touched. Spines are occasionally white, and young urchins sometimes have banded spines
Maximum Size: 7.5 cm (3 in) test diameter excluding spines
Longevity: Up to 5 years
Status: Not currently on the IUCN endangered species list
Long-Spined Urchin & People: The gonads (reproductive tissue) of long-spined urchins are consumed on some Caribbean islands, but collection is small scale. The main importance of the long-spined urchin to fisheries is through the reduction of algae. Long-spined urchins help control algae growth, which in turn promotes coral growth. Longspined urchins were one of the greatest consumers of algae on Caribbean coral reefs, but in 1984 a pathogen killed 95% – one of the most severe die-offs ever recorded in the Caribbean. Algae cover subsequently increased between 100% and 250%
Where?
Geographical Range: Found throughout the Caribbean, Florida, Gulf of Mexico and south to Brazil, as well as along Africa’s west coat
Coral Reef Zone: Found in all coral reef zones
Favourite Habitat: Long-spined urchins are commonly found on hard reef substrate, but are also found on sand or in seagrass beds
Depth Range: 0–400 m (0–1312 ft)
A Day in The Life:
Dawn: Urchins seek shelter in shady crevices
Day: The day is spent hiding in reef cracks and crevices; limited feeding may occur
Dusk: Urchins leave their daytime shelters from about 3 P.M. onwards and begin feeding; spawning may also occur
Night: Urchins are most active between midnight and 3 A.M., when they graze on algae
Who Eats Who
Long-spined urchins eat most types of algae that grow on coral reefs and seagrass leaves, including red, green, brown, and blue-green algae. Its pedators include crabs, starfish, and fish such as grunts, porcupinefish, queen triggerfish and Spanish hogfish.
Scuba Diver & Snorkeler Best Practices
Take care with fins A careless fin stroke can break coral and stir up sediments that reduce visibility, which in turn can reduce photosynthesis and smother the reef.
What?
Approach
Sea urchins are easy to approach. Most remain stationary as divers and snorkellers approach. Others may retreat into the reef structure. Sea urchins move very slowly using a combination of their spines and tube feet (also known as podia).
Feeding Behaviour Long-spined urchins are herbivorous, feeding actively on algae and detritus (dead and decaying matter) during the night. They move slowly around the reef using a combination of their spines and podia, and scrape at the hard reef substrate with sharp angular teeth located around their mouth on the underside of the urchin. Long-spined urchins sometimes graze the sandy area immediately around the reef they hide on. This has the effect of leaving behind a ring of bare seabed, called an urchin halo, which is especially apparent around patch reefs. The decrease in abundance of long-spined urchins is partly to blame for the massive increase in algae on Caribbean coral reefs, as sea urchins are one the reef’s most important grazers.
Observe, record & share:
O E.DA-101 – Feeding: Long-spined urchins use their spines and podia to move across the reef as they feed
O E.DA-102 – Urchin halo: Sea urchins leave a halo of grazed seabed around their home reef, often found around patch reefs
Attack & Defence Behaviour With their crown of long, sharp and toxic spines, sea urchins are well armoured against the attack of predators. However there are a number of species that still prey on the long-spined urchin including crabs, starfish, and fish such as grunts, porcupinefish, queen triggerfish and Spanish hogfish. Although they have no eyes to see predators coming, they do have a well-developed sense smell, and can detect the chemical odour of another injured sea urchin which suggests a predator maybe nearby. They can also detect the movement of water caused by an approaching object. Urchins in the open are vulnerable to attack and respond to threats by moving in the opposite direction, wedging themselves into reef cracks or crevices, and gathering together with other urchins in order to find safety in numbers. Divers and snorkelers may also notice sea urchins waving their spines in the general direction of the threat.
Observe, record & share:
O E.DA-201 – Hiding: Urchins hide in reef cracks and crevices for protection
O E.DA-202 – Retreating: Urchins may retreat from a potential predator if they feel threatened
O E.DA-203 – Aggregating: Urchins group together when threatened
O E.DA-204 – Spine waving: Urchins wave their spines in the general direction of the threat
Reproductive Behaviour Long-spined urchins practice broadcast spawning around the new moon, between May and December, with a peak in the late summer. During the spawning season, male and female urchins gather in groups around dusk. When an urchin is ready to spawn, it releases a chemical signal into the water that makes every urchin around it release their eggs or sperm at the same time. This mass release of gametes increases the chance that the eggs will be fertilized. Divers and snorkelers may see clouds of gametes released by spawning urchins, and in sufficient numbers, spawning urchins can even turn the water milky. The fertilized eggs then drift offshore, where they develop as part of the plankton, before returning to the reef and growing into adult urchins. Once the planktonic urchins settle on the reef, they can metamorphose into adults in as little as one hour.
Observe, record & share:
O E.DA-301 – Mating aggregations: Male and female urchins gather in groups at dusk
O E.DA-302 – Release of eggs and sperm: Male and females urchins release clouds of gametes into the water simultaneously
Highlight Behaviors
Symbiosis: The prickly spines of this sea urchin provide protection not only for the urchin itself, but also serve as shelter for a wide variety of small and otherwise defenceless reef organisms, including juvenile urchins (1). Look carefully within the spines of sea urchins and you may find juveniles of various different reef creatures, such as grunts, wrasses (2), butterflyfishes and lobsters (3), as well as adult organisms such as small shrimps (4), arrow crabs and the nimble spray crab (5). These creatures are small enough to hide within the spines of urchins and therefore benefit from greater protection against predators.
Did You Know?
• Larger urchins are often found in the prime locations on the edge of reefs, which are well protected and within easy reach of food, whereas smaller urchins are found in less desirable areas in the middle of reef.
• Some urchins have small bulb of tissue protruding from their upper surface, adjacent to the anus. This bulb is essentially an urchin ‘haemorrhoid’, and is believed to be caused by pressure build-up in the gut of the urchin.
• Sea urchin spines break off easily upon contact and become embedded in the skin. They also secrete a mild toxin that can make such an injury very painful. If you accidentally brush up against an urchin, first aid protocols commonly suggest using tweezers to remove any spines that protrude from the skin and applying a mild acid, such as lemon juice or vinegar, to reduce the burning sensation.
• Although long-spined urchins have no eyes, they can detect changes in light levels as light interacts with the sensitive nervous system that lies just beneath their very thin skin. In the daytime, an urchin’s skin flushes with dark pigments to protect this sensitive nervous system, but at night the pigments recede and the exposed nervous system can sense the early light of dawn and warn urchins to return to their shelters before sunrise.
What to do ?
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Observation Key
O Easy
O Not so easy
O Tough
