Diet

• Diadema mexicanum is primarily a grazing sea urchin that feeds on algae growing on rocks and coral substrates. It also consumes organic material associated with the seafloor. Its grazing removes algae and contributes to the maintenance of open surfaces on tropical Pacific reefs.

• Its feeding activity also removes carbonate material from reef substrates, making D. mexicanum an important bioeroder as well as a grazer.

Range

• The Needle Sea Urchin is native to the tropical eastern Pacific, occurring along the Pacific coast of Mexico and southward through Central America to northern South America and offshore eastern Pacific islands.

• It is abundant along the southern Mexican Pacific coast, including Guerrero. It is particularly well represented around Ixtapa-Zihuatanejo, where it was one of the dominant echinoderms recorded on local coral reefs.

Habitat

• Diadema mexicanum is a benthic marine species associated primarily with rocky bottoms and coral reefs in shallow subtidal water. Its reported depth range extends from the surface to approximately 104 m, although it is particularly conspicuous on shallow tropical reefs.

• Around Ixtapa-Zihuatanejo, it inhabits fringing coral reefs and rocky reef communities in protected bays and areas sheltered from heavy wave action. The local reef sites studied were generally no deeper than 12 m.

• It is commonly found in crevices and among rocks during the day, with its long spines providing protection from predators. Its abundance and grazing activity can have a significant influence on the amount of algal growth covering reef surfaces.

Description

• The Needle Sea Urchin has a rounded to slightly flattened test covered by extremely long, slender, brittle spines. The spines are typically black or very dark purple and can be several times the diameter of the test, giving the animal its characteristic needle-like appearance.

• The test is generally dark, with the fivefold radial arrangement characteristic of sea urchins. Small iridescent blue to blue-green spots may be visible between the bases of the spines.

• The long spines are an effective defence against predators and are easily broken when touched. Despite their intimidating appearance, D. mexicanum is not considered dangerous to humans, although broken spines can penetrate the skin.

• In Zihuatanejo, its dense aggregations can be particularly conspicuous on shallow coral reefs, where the dark spines contrast strongly with the lighter rock and coral substrate.