Black sea urchin

Echinoderm

Identification & Biology

• IdentificationA medium-sized sea urchin with a flattened, dome-shaped test (shell) covered in short, dense, dark purple to black spines. The spines are blunt-tipped and relatively uniform in length. The mouth is on the underside, equipped with a five-toothed feeding apparatus called Aristotle's lantern.
• SizeTest diameter up to 6 cm (excluding spines). Total diameter with spines up to 10 cm.
• Social HabitGregarious. Often found in dense aggregations on rocky surfaces, sometimes creating barren zones where all algae have been grazed. Active day and night.
• HabitatRocky reefs and hard substrates, particularly in shallow, well-lit areas. One of the dominant grazers on Mediterranean rocky reefs.
• Depth0 to 30 m. Most abundant between 1 and 15 m.
• Feeds OnCoralline algae, encrusting organisms, and biofilm scraped from rock surfaces. A powerful grazer that can create and maintain urchin barrens.
• DistributionEastern Atlantic from the Azores to the Mediterranean and West Africa. Very common in Maltese waters.
• DescriptionArbacia lixula is a dominant grazer on Maltese rocky reefs. In areas where predators such as fish and octopus are scarce, its populations can explode and strip rocks bare of all algal growth, creating grey, barren patches known as urchin barrens. Its ecological impact on Mediterranean reef communities is significant and well studied.