10 species you can spot at Aldinga’s intertidal and subtidal reefs

10 species you can spot at Aldinga’s intertidal and subtidal reefs

Locat­ed rough­ly 46 km south of Ade­laide, Aldin­ga Reef is teem­ing with sea life to be discovered.

Aldin­ga Reef forms part of the Great South­ern Reef, a reef sys­tem that fringes rough­ly 71,000 square km of the south­ern Aus­tralian coast­line, from West­ern Aus­tralia down and all the way around to New South Wales.

The Great South­ern Reef is a bio­di­ver­si­ty hotspot and is home to many species that aren’t found any­where else in the world – so there’s a lot to be seen and explored down at Aldinga.

And what’s even cool­er is that Aldin­ga has both a sub­ti­dal and inter­tidal reef.

Sub­ti­dal is the area below the low tide mark that is always cov­ered by water, and inter­tidal is the area that is cov­ered at high tide and exposed at low tide.

This means Aldin­ga Reef can be explored from the water and the land, mak­ing it one of South Australia’s most acces­si­ble reefs.

Keen for a vis­it? Here are 10 funky species to look out for, from the water and the land:

From the water

Try to spot these 5 bright­ly coloured inver­te­brate species next time you snorkel Aldinga’s sub­ti­dal rocky reef:

1. Fire-brick star (Pen­tag­o­naster dubeni)

The fire-brick staris a species of starfish and is eas­i­ly recog­nis­able for its bright yel­low, orange and red colouration.

Arm-length and plate-size of the fire-brick star varies, and they can be up to 15 cm at their widest point.

These guys live in rocky reefs and around soft sed­i­ment, up to 200 m below sea lev­el, but are most often seen in shal­low, shel­tered bays. 

(Image courtesy of D Easton)
(Image cour­tesy of D Easton)

2. West­ern slate-pen­cil urchin (Phyl­la­can­thus irreg­u­laris)

The west­ern slate-pen­cil urchin is named for its thick blunt spines around the body that look a lit­tle like pencils.

These urchins live in rocky reefs and are found up to 20 m below sea level.

Dur­ing the day the species use their spines to wedge them­selves firm­ly into holes and crevices, and at night-time they come out to feed using the 5 sharp teeth on their underside.

These guys feed on encrust­ing inver­te­brates and scav­enge dead and dying ani­mals – tasty!

10 species you can spot at Aldinga’s intertidal and subtidal reefs

3. Orange feath­er star (Coman­thus tri­choptera)

The orange feath­er star is the largest and most com­mon­ly seen feath­er sea star on shal­low reefs.

Indi­vid­u­als vary in colour, but they’re most com­mon­ly orange, brown, red or yellow.

If you spot one of these crit­ters, you’re like­ly to just see their extend­ed feed­ing arms as their bod­ies are usu­al­ly hid­den in a reef crevice.

(Image courtesy of H Crawford)
(Image cour­tesy of H Crawford)

4. Short tailed nudi­branch (Cer­ato­so­ma bre­vi­cau­da­tum)

The short tailed nudi­branch is one of many species of sea slug to be found in South Aus­tralia, and grow­ing up to 15 cm long means it’s also one of the largest.

These crit­ters are a vivid pink-orange colour with numer­ous red, white-edged spots over their bod­ies. You’ll find them in rocky reefs, up to 100 m deep.

(Image courtesy of H Crawford)
(Image cour­tesy of H Crawford)

5. Giant Aus­tralian cut­tle­fish (Sepia apa­ma)

Giant Aus­tralia cut­tle­fish are the most abun­dant local species of cut­tle­fish, and grow­ing up to 60 cm long and weigh­ing 5 kg they’re also the largest – and by a long shot at that!

The species is found amongst rocky reefs and sea­grassand can rapid­ly change colour and pat­tern to blend in with its surroundings.

Giant cut­tle­fish breed in the win­ter, where they put on a mat­ing dis­play that is some­thing to behold.

(Image courtesy of Carl Charter)
(Image cour­tesy of Carl Charter)

On land

If you want to explore the reef but aren’t keen on get­ting wet, wor­ry not! An inter­tidal reef ram­ble at Aldin­ga Reef is the per­fect way to explore. Here’s 5 species to look for:

1. Reef crab (Ozius trun­cates)

Reef crabs, also known as black fin­ger crabs, are red-brown in colour, have dark claws and can be found on rocky shores under loose rocks and boulders.

Males are big­ger than females, grow­ing up to 6 cm, and have larg­er claws to match.

These guys have a diet of inter­tidal reef snails, like con­ni­winks and black ner­ites – did some­body say gourmet?

(Image courtesy of J Baker)
(Image cour­tesy of J Baker)

2. Dog whelk (Dicathais orbi­ta)

Don’t be fooled by the name, dog whelk is a species of preda­to­ry sea snail and plays an impor­tant role on rock plat­forms, con­trol­ling pop­u­la­tion num­bers of bar­na­cles and mussels.

The shell shape of dog whelk varies with loca­tion, with low­er ridges occur­ring in exposed habitats.

These crit­ters grow up to 8 cm wide and are found in rocky reefs, up to 10 m deep.

(Image courtesy of D Easton)
(Image cour­tesy of D Easton)

3. Waratah anemone (Actinia tene­brosa)

The waratah anemone is a bright red-brown in colour and is named after the red waratah flower.

At low tide, when the body of the anemone is exposed to air, the ten­ta­cles close up, mak­ing it look like a dark red blob of jelly.

The waratah anemone is a live-bear­ing species, and baby anemones are ful­ly formed when they come out the mouth of the parent.

(Image courtesy of J Baker)
(Image cour­tesy of J Baker)

4. Inter­tidal tube worm (Gale­o­lar­ia cae­spi­tosa)

The inter­tidal tube worm, also known as the Syd­ney coral worm, lives in hard, cal­care­ous tubes that are about 3 cm long and are often aggre­gat­ed on inter­tidal reefs and jet­ty piles. 

These worms each have a crown of black ten­ta­cles that is extend­ed at high tide to catch par­ti­cles from the water. 

The crown is cov­ered by a lid, called an oper­cu­lum, at low tide, to pro­tect it from dry­ing out. 

(Image courtesy of J Baker)
(Image cour­tesy of J Baker)

5. Var­ie­gat­ed limpet (Cel­lana tramoser­i­ca)

There are many species of limpets in South Aus­tralia, and the var­ie­gat­ed limpet is one of the more abundant.

The var­ie­gat­ed limpet is gold­en brown with dark­er stripes, and grows to about 6 cm. 

Found on inter­tidal reefs, it grazes on algae (which in turn helps to con­trol algae). 

After mov­ing around to feed, some of these limpets return to the same place on their home’ rock, by sens­ing the chem­i­cals in their own slime trails.

(Image courtesy of J Baker)
(Image cour­tesy of J Baker)

Top tips for a great trip

  • Always check the weath­er before plan­ning a snorkelling trip
  • Low tides of 0.3 m or less are best for inter­tidal reef ram­bles, because you’ll be able to access the far edge of the inter­tidal reef and see more marine life
  • Always make sure some­one knows where you’re going, and what time you’ll be back
  • Look, but don’t touch – Aldin­ga Reef is part of a sanc­tu­ary zone, which means it’s ful­ly pro­tect­ed, so you can’t take any­thing home with you


If you’re an expe­ri­enced snorkel­er, head to the edge of the reef dur­ing low tide when sea con­di­tions are flat. 

If you don’t have much expe­ri­ence snorkelling, try explor­ing the calm tidal pools of the south­ern part of the reef – access is between Seav­iew Road and Aldin­ga Beach Road.

If you would like to dis­cov­er the amaz­ing marine life of South Australia’s sub­ti­dal reefs but don’t have the expe­ri­ence or con­fi­dence to go snorkelling, then check out Expe­ri­enc­ing Marine Sanc­tu­ar­ies’ web­site for infor­ma­tion on their reg­u­lar guid­ed group snorkelling tours.

Want more? Check out Nation­al Parks and Wildlife Service’s beach­comb­ingand snorkel­er’sguides to find out more about the plants and ani­mals you might see on the beach or while snorkelling in our marine parks.

This con­tent was pro­duced in part­ner­ship with  Good Living