Red Knob Sea Star

Care at a glance

Overview

Not reef safe: as it grows it becomes an active predator of soft corals, sponges, tube worms, clams, and even other sea stars, so like its chocolate chip relative it is strictly a fish-only-with-live-rock animal, never a reef tank one. Small juveniles graze more on algae and biofilm and can look deceptively harmless, but that does not last, since the same animal turns predatory as it matures. Feed it chopped clam, shrimp, squid, or fish once or twice a week; it scavenges the rest of the time and will not go hungry between meals. Use a slow drip acclimation and keep salinity and pH stable during introduction, since like every sea star here it is intolerant of sudden water chemistry swings even though it is otherwise a tough, easygoing animal once established.

In the wild

Found along the western Indian Ocean, mainly the East African coast and Madagascar, north to India and Sri Lanka, with a small isolated population off Western Australia, on sandy and muddy seabeds from shallow tidal pools down to about 100 m. It forages slowly over open bottom day and night, so it needs a soft sand substrate to move across plus enough floor space that it is not constantly climbing over rockwork or other tankmates. A tank of at least 200 litres (53 US gal) suits one of these large, heavy-bodied stars long term.

Good to know

Easy to tell apart from other large sea stars by its thick gray body and the rows of bright red, knob-like tubercles running along each of its five arms, connected by thin red lines into a pattern that looks almost like a wired grid. It belongs to family Oreasteridae, the cushion stars, alongside the chocolate chip star, and grows into one of the largest sea stars in the hobby at up to about 30 cm across. Wild populations are also collected and dried for the curio trade, particularly in Tanzania, where mummified specimens are sold as souvenirs.

Did you know

Despite its armor-plated look, it is a slow enough mover that it can end up prey itself: large triggerfish and pufferfish are known to flip and eat sea stars in the wild, part of why FOWLR tanks built around those fish are a poor match for it.

Related species

• 

  Chocolate Chip Star

  Protoreaster nodosus

  11.8 in (30 cm)53 gal (200 L)75–81°F (24–27°C)

• 

  Blue Linckia Star

  Linckia laevigata

  11.8 in (30 cm)53 gal (200 L)75–81°F (24–27°C)
• Wedge Sea Hare

  Dolabella auricularia

  11.8 in (30 cm)50 gal (190 L)75–81°F (24–27°C)

• 

  Long-Spine Urchin

  Diadema setosum

  9.8 in (25 cm)50 gal (190 L)72–79°F (22–26°C)

• 

  Tiger Tail Sea Cucumber

  Holothuria hilla

  17.7 in (45 cm)50 gal (190 L)72–79°F (22–26°C)

• 

  Serpent Star

  Ophioderma

  11.8 in (30 cm)26 gal (100 L)72–79°F (22–26°C)