Giant Horned Starfish Species

Identification

• These two large starfish species have starkly different appearances. The horned sea star can grow to be almost 1 foot in diameter. The horned sea star varies from white or cream color to dark orange, and it's covered by smallish horns that are dark blue, black or dark green. It has five stars, in the typical starfish shape.

  Although the horned sea star is large by starfish standards, it is dwarfed by the crown-of-thorns starfish, which can grow to more than 3 feet across. Crown-of-thorns starfish have up to 21 arms and are dark red, blue or black. They are covered in thorns, much more than the horned sea star, and the thorns are venomous.

Habitats

• The horned sea star is mainly found in Indo-Pacific waters, such as off Malaysia and Singapore. Near Singapore in particular, they are found sporadically on Chek Jawa and the northern and southern shores. This species is often found among coral rubble as adults, and in seagrass as juveniles, such as the seagrass in the Cyrene Reef.

  The crown-of-thorns starfish is also present in some of these waters, though it prefers South Pacific coral reefs as its habitat, particularly the Great Barrier Reef and similar areas nearby.

Feeding

• Both the horned sea star and the crown-of-thorns starfish feed like the majority of starfish species, turning their stomachs inside out from their mouths and digesting food with stomach enzymes. Horned sea stars, like most starfish, eat micro-organisms and dead sea creatures, including clams, snails, sponges and soft corals.

  Crown-of-thorns starfish eat live coral, which is unusual for starfish. Juveniles also eat encrusting coralline algae.

Crown-of-Thorns Outbreaks

• Crown-of-thorns starfish can pose a threat to coral reefs. Their sharp spines and large size mean they have no natural predators and can therefore overrun coral reefs when their population is allowed to thrive. The first record of this happening in the Great Barrier Reef was in 1962. Such outbreaks have occurred since then frequently. When populations explode, corals are eaten at a rate faster than they can recover from. Although this is a natural occurrence, human activities on the coast have released additional nutrients the starfish can use to reproduce in their habitat.