Diadema setosum

Diadema setosum is a species of sea urchin that can be found in Indo-Pacific waters. Its range extends from the Red Sea to coasts of Australia in the east, and from Japan in the north to the east coast of Africa in the south. There have been a few individuals found outside of this natural range, leading experts to believe that it was introduced by natural or manmade causes. Two individuals were found off the coast of the Kaş peninsula in Turkey in 2006. These individuals represent the first invasive species of Erythrean sea urchin in Mediterranean waters. This species prefers to reside within coral reefs, but will reside within seagrass beds or in sandy areas.

Diadema setosum is similar in appearance to all sea urchins, with a spherical body and long spines, sharp spines. Its test, or outer shell, can reach and average diameter of 2.7 inches and adults can weigh between 1.2 and 2.8 ounces. The internal structure of this species is typical to that of other types of sea urchins. Its organs are protected by a black test, which hold many straight spines of different lengths. These spines are hollow and are typically black in color, although some are banded with brown stripes. The spines contain venom, which the sea urchin uses for defense, but this venom is not known to be dangerous to humans.

Diadema setosum has many features, which help distinguish it from other sea urchins. The test holds five white spots, which are located along the ambulacral grooves, which no other members of its genus have. This species also bears an orange circle around its anus, often known as the periproctal cone. It also minor distinguishing marks, like bluish spots that appear in linear pattern along the test and on the plates that protect its reproductive organs.

The spawning season for Diadema setosum can vary depending upon its location, with spawning occurring both year round and seasonally. It is thought that temperature plays a large role in spawning, with many populations spawning when temperatures reach at least 77 degrees Fahrenheit. In equatorial areas like the Philippines, these sea urchins are able to breed throughout the year, while one population in the Persian Gulf was noted to spawn between the months of April and May. It is thought that the phases of the moon may affect the spawning season of this species as well, with many populations spawning when the moon is full.

The diet of Diadema setosum is typical of sea urchin species as it grazes on many types of algae found along the coral reef that it inhabits. Because this species, along with all sea urchins, can consume a large amount of algae, it is thought to possibly be threatened by habitat loss.

Image Caption: Diadema setosum in Prague sea aquarium, Czech Republic. Credit: Karelj/Wikipedia