【Reading】むらさきSea Urchin

【English Name】Purple sea urchin

The purple sea urchin (murasaki-uni) is an echinoderm belonging to the family Echinometridae and is one of the representative sea urchins widely used at Japanese sushi restaurants. The shell is about 5-6 cm in diameter, and it is characterized by the long, conspicuous spines covering its whole body. The dark purple body color is the origin of its Japanese name.

Its range extends along the entire coast from south of Aomori Prefecture on the Sea of Japan side and south of Ibaraki Prefecture on the Pacific side, and it is also found in southeastern China and the waters near Taiwan. It inhabits rocky shores to shallow areas and grows feeding mainly on seaweed. Its lifespan is said to be about nine years.

The edible part is the gonads (the so-called "flesh"), and the peak season is mainly around June to August, coinciding with the spawning period. Because the gonads are a pale yellowish-white, it is known as "white uni," in contrast to the "red uni" of the bafun-uni (green sea urchin) group. It is distributed collectively as white uni together with the northern purple sea urchin (kita-murasaki-uni), and it is not uncommon for the distinction between the two to become blurred at market.

Because it has a tendency for the flesh to break apart as freshness declines, it is customarily shipped nationwide in the form of "ita-uni" (board uni), treated with alum to prevent the shape from collapsing. At producing areas it is also offered as salt-water-soaked uni or served in the shell, and as "shio-uni" (salted uni).

In recent years its connection to the "isoyake" (rocky-shore barrens) phenomenon, in which seaweed is lost, has been debated, and in Kanagawa Prefecture trials of aquaculture using cabbage as feed (popularly called "cabbage uni") are being researched and promoted.