Blue Sea Star
Linckia laevigata
Photo by Claire Guillaume, 2013
The blue sea star is one of the most abundant invertebrates on Australian reefs, and this one was found in our own backyard here at Gnaraloo. Blue sea stars can live up to 10 years in the wild and are highly sensitive to light, temperature, and tide despite their lack of cephalisation (meaning they don’t have a head!). Adults have a wide variety in their diet which includes everything from small invertebrates to detritus. Lastly, sea stars eat by inverting their stomachs and digest food externally before returning it inside the body.
Sea Hare
Aplysia sp.
Photo by Simone Bosshard, 2018
While many people mistake these molluscs for seaweed, we can assure you that they are in fact an animal! Sea hares are a close relative of the sea slug or the nudibranch and often wash up on beaches during late summer and throughout autumn. The common name, sea hare, refers to the large tentacles found on the left side of this photo that resemble the large ears of a rabbit. Much like octopods, sea hares release a purple dye when they are threatened that works as a smoke screen, allowing them to escape from predators. These organisms live for about a year and form long egg chains during mating that are released as long strings in summer. They are found in many regions through-out the world, so next time you are on the beach keep your eyes peeled for sea hares disguised as seaweed!
Bluebottle (Portuguese Man-of-War)
Physalia physalis
Photo by Heather Shipp, 2017
The bluebottle or Portuguese man-of-war can be found at many beaches around the country. This cnidarian is not actually a single individual, but in fact a colony of four kinds of highly modified individuals, called zooids. The float (pneumatophore) is a single individual and provides support for the rest of the colony. The tentacles (dactylozooids) detect and capture food and drag the prey into the range of the digestive polyps (gastrozooids). The final polyp is called a gonozooid and is used to carry out reproductive activities. Similarly to jellyfish, bluebottles have stinging capsules that contain a toxic mixture of phenols and proteins that are injected into the victim to seize prey items.
Golden and Horn Eyed Ghost Crabs
Ocypode convexa, ceratophthalma
Photo by Claire Guillaume, 2013
Here at Gnaraloo we have a special love/hate relationship with ghost crabs. Most commonly, we see the endemic golden ghost crab (Ocypode convexa) but it is also likely to encounter the horn-eyed ghost crab (Ocypode ceratophthalma) on our beaches. Ghost crabs are among the fastest land creatures, moving at 100 body lengths per second- almost 10 times faster than a cheetah – giving them a ghostly ability to suddenly appear and disappear in the blink of an eye. These two species of crab are present in the thousands at Gnaraloo and serve as the largest natural predator to loggerhead sea turtles on the west coast of Australia. The curious crabs burrow into turtle nests and run off with both eggs and hatchlings, leaving a trail of eggshells and hatchling flippers as evidence of their intrusion.
Day Octopus
Octopus cyanea
Photo by Simone Bosshard, 2017
The day octopus is a large octopus with a body up to 20 cm and arms reaching 80 cm each. They are typically brown in colour but have the ability to rapidly change colour and skin texture to resemble the ocean substrate, making them nearly invisible to predators. While most species of octopus forage at night, the day octopus is crepuscular, hunting mostly at dusk and dawn. Octopi are predators and often search for crabs, shrimp, and fish, killing their prey with an injection of toxic saliva or with their strong beak. Once the octopus kills its prey, it will store the empty mollusc shells outside its den in a pile commonly called an “octopus garden.” In the photo you can see a battle between the endemic golden ghost crab (Ocypode convexa) and the octopus, we didn’t stick around but we can all guess who won!
Sand Dollar
– – –
2017
A Sand Dollar is the endoskeleton of a flat sea urchin. It belongs to the phylum Echinodermata, making it related to other sea urchins, sea stars, and sea cucumbers. The skeleton of a sand dollar is rigid and composed of calcium carbonate plates. It has a five-part radial symmetry and five petal-shaped perforations containing podia, which are used in part for respiration. Its epidermis is covered in dense spines that are used to slowly move itself along the sandy ocean floor, burrow into the sand to seek protection, and guide food particles into its mouth, which is located in the centre of its bottom surface. Although washed up sand dollars on the beach are commonly bleached by the sun, they are usually darker in colour, such as green or purple, while still alive in the water.
Cuttlefish
Sepia spp.
Photo by Lisa Georgiou, 2016
Decorator Crab
Naxia tumida
2016
Giant Clam
Tridacna gigas
Photo by Simone Bosshard, 2017
Grapsus albolineatus (Sally Lightfoot Crab)
Grapsus albolineatus
2011
Greater Blue-Ringed Octopus
Hapalochlaena lunulata
Photo by Stephanie Whelan, 2017
Purple Rock Crab
Leptograpsus variegatus
Photo by Claire Guillaume, 2013
Red Knob Sea Star
Protoreaster lincki
Photo by Stephanie Whelan, 2017
Shame-faced Crab
Calappa calappa
Photo by Ludmila Segato, 2017
Spanish Dancer
Hexabranchus sanguineus
Photo by Stephanie Whelan, 2017
Spiny Sea Urchin
Centrostephanus rodgersii
Photo by Stephanie Whelan, 2017
White-Spotted Hermit Crab
Dardanus megistos
Photo by Jeremie Collado, 2017
Western Australian Nudibranch
Chromodoris westraliensis
Photo by Jeremie Collado, 2017
Have you seen animals that are not listed here?
Please submit your photos of what you saw at Gnaraloo – on land or in water – with a species identification.
Find more species identifications in the Gnaraloo Snorkel Guide by Denise Jenkins available at Gnaraloo Station.
