Asterina Starfish

Asterina stars are tiny sea stars, rarely larger than one centimeter, that suddenly appear on the glass and rocks of reef aquariums. They are not bought; they arrive together with live rock and coral frags. Because they reproduce by splitting their bodies in two, their arms are often unequal; individuals with six or seven arms and one short side are common. Those in aquariums mostly belong to the genus Aquilonastra; identifying the exact species is difficult, and some populations behave differently from others.

• It lives on its own in reef aquariums of every size; it can multiply even in 20-liter nano reefs.
• Salinity 1.023–1.026 specific gravity, pH 8.1–8.4, temperature 24–27°C.
• Mostly reef-safe; but in some aquariums it is reported to eat the tissue of corals such as zoanthids and Acropora. If stars are seen feeding on coral tissue, they should be removed by hand or with a siphon.
• Copper-based medications are lethal.

It feeds on algal film, biofilm and leftover food on the glass and rocks. Overfeeding and high nutrient levels lead to a rapid increase in their numbers.

More active at night. As long as their numbers are under control they behave like harmless cleaners; when they multiply excessively, the risk of them turning to corals increases.

Good companions: almost all reef animals; because it hunts Asterina, the harlequin shrimp can keep them under control.

Avoid: delicate zoanthid and Acropora colonies in aquariums where Asterina have been seen feeding on coral tissue.