Black Sea Urchin

Overview

The black sea urchin (Arbacia lixula) is a medium-sized, hemispherical echinoderm widely distributed across the Mediterranean Sea and parts of the Atlantic Ocean. It is a prominent herbivore in rocky coastal ecosystems, where it plays a key role in regulating algal growth and maintaining the balance of marine habitats.

Appearance

This species is easily recognized by its deep black to dark-brown coloration and uniform, erect spines that lack the dishevelled appearance of other urchins. Unlike similar species, it features a distinct anal valve composed of four plates on its upper surface. The oral side is largely naked, with the mouth area surrounded by soft, dark-greenish skin.

Biology & behavior

Arbacia lixula is well-adapted to high-energy environments, possessing strong attachment capabilities that allow it to cling to rocks even in areas with significant wave action. While primarily diurnal, some populations have been observed adjusting their grazing patterns to be more nocturnal depending on environmental pressures. They are sensitive to water quality and temperature, with their larvae showing a broad thermal tolerance that supports population connectivity across different regions.

Feeding

As a dedicated herbivore, this urchin acts as a "gardener of the sea." It feeds primarily on crustose red algae and small filamentous algae, often leaving behind distinct grazing trails on the rocky substrate. By controlling algal cover, they can significantly influence the structure of their local marine environment.