- Eight-armed seastars are a common medium-sized, brightly coloured sea star with a mottled pattern that varies from grey, blue, green, red, orange, cream, white, mauve, black or brown.
- They normally have eight arms, although occasionally they can have seven or nine.
- The body is circular, with the arms short and thick but individually recognisable (i.e. not webbed)
- Size: Arm radius up to 5 cm across
What to Observe
Search area for 30 minutes and record under the following categories-
- Abundant - found easily with little searching
- Frequent - found with minimal searching
- Rare - only 1 or 2 individuals found with intensive searching
- Not found - not present during search
ClimateWatch Science Advisor
As a result of climate change, warm tropical ocean currents are expected to strengthen and persist for longer periods in southern coastal area normally dominated by cooler waters. The consequent increases in water temperature are likely to result in unfavourable growing conditions for echinoderms or their food sources which many result in changes to the food web.
When To Look
Throughout the year
Where To Look
- Common on rocky shores, from mid tide levels. Usually found rock pools, crevices and wet areas.
- Albany WA, SA, TAS, VIC, NSW up to Currumbin QLD
Davey, K. (1998). A Photographic Guide to Seashore Life of Australia. New Holland Publishers Australia Pty Ltd.
Edger, GJ. (2008). Australian Marine Life. The Plants and Animals of Temperate Waters [2nd Ed]. New Holland Publishers Australia Pty Ltd.
Most other seastars have five, seven or eleven arms which help to distinguish the eight arm seastars from these species. The many armed sea star (Allostichaster polyplax) can also have 8 arms but will often has several arms smaller than the rest and its main habitat is under rocks. A distinguishing feature of the eight arm seastar is its uniform pale colour ( white, cream or yellow) on the underside of its body, which differs from the other common species of seastar found on rock platforms (five armed sea star Patiriella exigua) being light grey to green in colour underneath.
Did You Know?
Eight-armed seastars eat “detritus”, which means any decomposing organic matter lying on the bottom such as dead seaweed (algae), marine snails (molluscs) or fish, but they also eat living algae.
If an eight-armed seastar loses and arm it can grow it back, and if the lost arm has a piece of the central disc still attached it will regrow its other legs to form a new seastar.