Red knob sea star

Care at a glance

Overview

The red knob sea star is one of the largest sea stars in the hobby, and it belongs in a fish-only tank. It is an easy keeper.

Caring for the red knob sea star

Keep the red knob sea star in a fish-only tank with live rock, never a reef. As it grows, it becomes an active predator of soft corals, sponges, tube worms, clams and even other sea stars. Small juveniles graze more on algae and biofilm and can look harmless, but they turn predatory as they mature.

Give this large, heavy-bodied star at least 53 gal (200 L) for the long term, with a soft sand substrate. It needs enough floor space that it is not constantly climbing over rockwork or tank mates.

Hold the water at 75 to 81°F (24 to 27°C) with a pH of 8.1 to 8.4. Use a slow drip acclimation, and keep salinity and pH stable during introduction. It cannot take sudden swings in water chemistry, though it is tough and easygoing once established.

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. A fish-only tank built around large triggerfish or pufferfish is a poor match for it.

Good to know

The red knob sea star is easy to tell apart from other large sea stars by its thick gray body. Rows of bright red, knob-like tubercles run along each of its five arms. Thin red lines connect them into a pattern that looks almost like a wired grid. It belongs to the family Oreasteridae, the cushion stars, alongside the chocolate chip star. It is also sold as the African sea star or red spine star. Wild populations are also collected and dried for the curio trade, particularly in Tanzania, where mummified specimens are sold as souvenirs.

In the wild

The red knob sea star lives along the western Indian Ocean, mainly the East African coast and Madagascar, north to India and Sri Lanka. A small, isolated population lives off Western Australia. It is found on sandy and muddy seabeds, from shallow tidal pools down to about 100 m. It forages slowly over open bottom day and night.

Common questions

Related species

• 

  Chocolate chip star

  Protoreaster nodosus

  11.8 in (30 cm) · 53 gal (200 L)

  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)

  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)

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

• 

  Fire urchin

  Asthenosoma varium

  9.8 in (25 cm) · 201 gal (760 L)

  9.8 in (25 cm)201 gal (760 L)72–81°F (22–27°C)

• 

  Long-spine urchin

  Diadema setosum

  9.8 in (25 cm) · 50 gal (190 L)

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

• 

  Blue spot urchin

  Astropyga radiata

  7.9 in (20 cm) · 100 gal (380 L)

  7.9 in (20 cm)100 gal (380 L)72–82°F (22–28°C)