Diadema setosum is a widely distributed species of sea urchin.
Its range stretches throughout the Indo-Pacific basin, longitudinally from the Red Sea and then eastward to the Australian coast.
Latitudinally, the species can be found as far north as Japan and its range extends as far south as the southern tip of the African east coast.

The species has been introduced into other localities not within its natural range.
In 2006, two living specimens of Diadema setosum were found in waters off the Kaş peninsula in Turkey.
The discovery and subsequent collection of these individuals makes D. setosum the first invasive Erythrean sea urchin in the Mediterranean.
Several hypotheses have been proposed for the finding of these individuals.
Larvae of the species may have traveled through the Suez Canal (Lessepsian migration) into the Mediterranean from the Gulf of Suez, where the species has a thriving natural population.
Another proposed vector is that of foreign ships bringing in individuals via their ballasts.
A final possibility proposed was that the individual specimens were intentionally released by aquarists.

Diadema setosum is commonly associated with coral reefs, but is also found on sand flats and in seagrass beds.
Along with the other members of the family, D. setosum is a prolific grazer.
They are known to feed on a variety of algal species common on tropical coral reefs.
The ecological importance of the taxon as a whole has been stressed because of its herbivorous habits.

In Hong Kong, Diadema setosum is omnipresent in rocky reefs, with a population density of up to one individual per 3.4m².
The unusually large number of these urchins is theorised to be partly natural, and partly due to overfishing of its primary predator in the region, the blackspot tuskfish (Cheorodon schoenleinii).
Diadema setosum is a widely distributed species of sea urchin. Its range stretches throughout the Indo-Pacific basin, longitudinally from the Red Sea and then eastward to the Australian coast. Latitudinally, the species can be found as far north as Japan and its range extends as far south as the southern tip of the African east coast.
The species has been introduced into other localities not within its natural range. In 2006, two living specimens of Diadema setosum were found in waters off the Kaş peninsula in Turkey. The discovery and subsequent collection of these individuals makes D. setosum the first invasive Erythrean sea urchin in the Mediterranean. Several hypotheses have been proposed for the finding of these individuals. Larvae of the species may have traveled through the Suez Canal (Lessepsian migration) into the Mediterranean from the Gulf of Suez, where the species has a thriving natural population. Another proposed vector is that of foreign ships bringing in individuals via their ballasts. A final possibility proposed was that the individual specimens were intentionally released by aquarists.
Diadema setosum is commonly associated with coral reefs, but is also found on sand flats and in seagrass beds. Along with the other members of the family, D. setosum is a prolific grazer. They are known to feed on a variety of algal species common on tropical coral reefs. The ecological importance of the taxon as a whole has been stressed because of its herbivorous habits.
In Hong Kong, Diadema setosum is omnipresent in rocky reefs, with a population density of up to one individual per 3.4m². The unusually large number of these urchins is theorised to be partly natural, and partly due to overfishing of its primary predator in the region, the blackspot tuskfish (Cheorodon schoenleinii).
Diadema setosum