Longspined sea urchin

Diadema savignyi

ORDER

Diadematida

FAMILY

Diadematidae

TAXONOMY

Diadema savignyi Michelin, 1845.

H Abatus coratus H Astropyga magnifica H Anthocidaris crassispina

OTHER COMMON NAMES

English: Blue eye urchin, black long-spined urchin. PHYSICAL CHARACTERISTICS

Relatively flattened, but oval test that can reach 3.1 in (8 cm) in diameter. Distinctive long and slender black or while spines, which vary in length from 1.9-3.9 in (5-10 cm). Test and spines are fragile. It has a distinctive iridescent blue ring around anus. Often mistaken for D. steosum, which has an orange ring. Darker animals tend to exist in the open on sand, whereas paler colored animals live in crevices or in turbid waters.

DISTRIBUTION

A ubiquitous shallow water species found throughout the Indo-Pacific and South Pacific Oceans to a depth of 1,312 ft (400 m).

HABITAT

Usually found inhabiting sheltered areas of coral reefs on rocky substrata or sandy lagoons, but occasionally occur in sea grass beds.

BEHAVIOR

An active animal that is highly responsive to changes in light intensity. Often the test color will change according to changes in light. High densities may provide protection against predators. A variety of commensals associated with urchins, living among the spines, ranging from small shrimps and mysids to juvenile fish.

FEEDING ECOLOGY AND DIET

Voracious grazer of algal turf. Following unexpected mass mortalities, growth of algae is usually rapid and detrimental to many coral reefs globally. Tend to hide during the day in rocky crevices, but forage for food at night. Has many predators, mostly fish, mollusks, and crustaceans.

REPRODUCTIVE BIOLOGY

Sexual reproduction; depending on geographical location, known to aggregate during spawning. Release of eggs and sperm into the water column coincides with the lunar cycle usually between summer and early winter.

CONSERVATION STATUS Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

Considered ecologically important to many coral reef ecosystems. Spines are poisonous and easily puncture human skin, often leaving infection. ♦

PHYSICAL CHARACTERISTICS

Size variable, but commonly occurring between 0.8 and 2 in (2-5 cm) in diameter. Have black to dark violet coloration, with short spines.

DISTRIBUTION

Commonly found inhabiting the lower intertidal and shallow subtidal areas throughout the coastal waters of southern China, where it is an important benthic grazer of many algae-dominated communities.

HABITAT

Rocky shores are their principle habitat, where they appear to be well adapted to living in crevices and rock pools, especially on wave-exposed shores. Geographical distribution is limited by saline conditions; urchin densities tend to be lower on the oceanic southern and eastern coasts of Asia. When found on sand, their spines are usually covered in algae and shell fragments to camouflage them from predators.

BEHAVIOR

Foraging activities are predominately nocturnal, although movements during the day correlate with changes in seawater depth during the tidal cycle.

FEEDING ECOLOGY AND DIET

Grazer, feeding mainly on encrusting algae (e.g., Corallina, Sargassum, Colpomenia, and Ulva), although the diet broadly reflects their seasonal availability. During the summer months, when the availability of prey is generally low, the diet is dominated by Corallina. Occasionally, other small organisms are consumed, such as bivalves and crabs.

REPRODUCTIVE BIOLOGY

Sexual reproduction; spawning usually occurs between July and September, depending on seawater temperature. Broadcast fertilized eggs into the water column. Larvae undergo planktonic stage before settling to the seafloor.

CONSERVATION STATUS Not listed by the IUCN.

SIGNIFICANCE TO HUMANS

Commercially harvested for roe in the coastal waters of Asia. Also used as an indicator species for toxic chemicals in the marine environment. The occurrence of an indicator species is usually associated with impacts from anthropogenic activity, such as high concentrations of chemicals released from outfalls, or industrial spill run off from the land into the sea.4

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