Echinoderms of the Asia/Indo – Pacific
With many hundred species well documented, and new species being discovered all the time, Australasian sea stars have a great potential for the enthusiastic underwater photographer and underwater naturalist.
Although many species of sea stars, otherwise referred to as starfish, are known to exist, very few studies (apart from those being carried on by the Victorian Museum and Western Australian Museum have been done on the natural histories, or behaviours of Australian and Indo – Pacific species.
COMMON NAME: RHINOCEROS SEA STAR
SCIENTIFIC NAMES: Protoreaster nodosus
5 metres Kapali, Sabah, Malaysia
Very variable in colour this is a very common widely distributed species which can be seen in shallow water sea grass meadows from the Red Sea to the islands of the South Pacific. It grows to around 250 mm and is a detrital feeder. It provides a habitat to a number of commensals, including scale worms, shrimps and crabs and plays host to several parasitic molluscs.( photo: Neville Coleman)
COMMON NAME: COLEMAN'S NIPPLED STAR
SCIENTIFIC NAMES: Gomophia sp.
20 metres, Moreton Bay, Queensland Australia
First discovered by the author at Swain's Reefs in the early 1980's this species has now been found at the Maldives and also at Moreton Bay, Queensland. It grows to 200 mm and has been found on rubble bottom around 20 to 30 metres. Little is known of its natural history and the species is still considered to be rare. It is hoped that its description will be published in the near future.( photo: Neville Coleman)
The are hundreds of unknowns and a thousand questions that require answering to increase our knowledge of sea stars. Although sea stars may look slow and uninteresting, they have amazing behaviour and bizarre natural histories and are unique amongst all the other sea life in our oceans.
I have done my bit to advance their knowledge in my book SEA STARS - Echinoderms of the Asia/Indo - Pacific, but there is still a long way to go.
All sea stars have the same basic star shape and most have five arms. There is a mouth on the underside; the anus (where present) is at the centre of the disc on the dorsal surface, together with the water intake (madreporite) off to the side.
COMMON NAME: BLUE SEA STAR
SCIENTIFIC NAMES: Linckia laevigata
2 metres, Great Barrier Reef
Although well known by its most common colour form, this species is subject to colour variation and may be pink, grey, brown, or yellowish. In one of its juvenile stages it is generally grey with darker patches.
It occurs on reef flats and in shallow water on coral reefs where it feeds on algae and detritus. The species reaches a size of 200 mm.( photo: Neville Coleman)
The body is covered by plates which may be large, or small, depending on the species. While some kinds appear soft, others give the impression of being quite rigid and cannot be bent even under pressure, breaking before they yield. These plates are often spiny, or modified in some way. In the case of the Crown of Thorns sea star, the plates are extremely modified and the spines have acquired venomous properties, and as such, are serious threats to scuba divers and snorkel divers.
Between the plates (which are embedded in the body walls) are soft tissue and small gills which are retractable. When these gills (papulae) are
extended they often give the sea star a soft, velvety appearance.
COMMON NAME: VELVET SEA STAR
SCIENTIFIC NAMES: Petricia vernicina
12 metres, Bass Strait Tasmania
Found from northern New South Wales south and around to South Western Australia the Velvet Sea Star is very slimy to touch and occurs in a number of colour variations, including red, orange, grey, white, lemon and purple. It feeds on sponges and has been recorded from Lord Howe Island and Norfolk Islands down to depths of 30 metres.( photo: Neville Coleman)
On the body surface there are other small organs peculiar to sea stars and sea urchins. These devices are known as pedicellariae of which there are three different types; simple, pincer-like and scissor-like. On sea stars, the pedicellariae are sessile, while on sea urchins they are on stalks.
The pedicellariae act as cleaning mechanisms and defence organs
(some are venomous, even deadly).
Beneath the underside of each arm there is an ambulacral groove which contains two rows of mobile tube feet (except in Asteriidae which have 4 rows). These locomotory tube feet are operated by water pressure and have suckers at the tips in reef-dwelling sea stars, or points for digging purposes on some sand-dwelling sea stars.
COMMON NAME: COMB SEA STAR
SCIENTIFIC NAMES: Astropecten polyacanthus
20 metres, Moreton Bay Queensland Australia
Sand stars like this species have pointed tube feet, while the reef sea stars have tube feet tipped with suckers. The Comb Sea Star spends most of its life buried in the substrate and only emerges if it is discovered by a predator , or comes up in search of food which consists of small bivalves. Very widely distributed it occurs from the Red Sea to New Zealand, Lord Howe Island and New Caledonia. ( photo: Neville Coleman)
Reef-dwelling sea stars are sometimes found on sand and soft bottom, but sand-dwelling forms (with pointed tube feet) are unable to climb on rocky reefs and would have difficulty finding food. All sea stars can regenerate damaged or missing parts.
The majority of sea stars are carnivorous though different species may be herbivorous, carnivorous, omnivorous and/or detritus feeders, or scavengers, depending on what's available. Food is generally absorbed outside of the mouth by way of extruding the stomach over the prey and dissolved with powerful enzymes, or in the case of some sand stars, the invertebrate prey is swallowed, or half swallowed (when too big) and eaten (dissolved) gradually inside the mouth cavity.
COMMON NAME: GLOBULAR SEA STAR
SCIENTIFIC NAMES: Echinaster glomeratus
20 metres Nuyt's Archipelago South Australia
Named since 1916 this spectacular sea star occurs along the southern coast of Australia from South Australia to South Western Australia. Colour can vary from bright yellow to wine red and it generally inhabits kelp beds where it feeds on sponges and ascidians. It occurs from low tide level down to at least 40 metres and is not considered common.( photo: Neville Coleman)
Food includes detritus, algae, seagrass, sponges, corals, worms, bryozoans, molluscs, crustaceans, echinoderms, ascidians, and almost anything dead. In turn, they are preyed upon by fish, molluscs, crustaceans and other sea stars.
COMMON NAME: FIREBRICK SEA STAR
SCIENTIFIC NAMES: Asterodiscides truncatus
23 metres, Cronulla, New South Wales Australia
Occurring from central New South Wales south and around to South Western Australia, this brilliant sea star is also found in Tasmania and New Zealand. It lives on rocky reefs and appears to feed on sponges and has been dredged up from 804 metres, so it covers quite a large area of sea floor. Adults reach a size of 200 mm and as there are no other similar species in diving depth it is an easy species to recognise and identify.( photo: Neville Coleman)
COMMON NAME: MOSAIC SEA STAR
SCIENTIFIC NAMES: Plectaster decanus
15 metres, Jervis Bay, New South Wales Australia
One of the few sea stars known to have venomous qualities, this species should not be picked up and held in the bare hand for any length of time. It is distributed from Southern Queensland south and around to South Western Australia where it inhabits rocky reefs and feeds on sponges. Over its range the colour varies, but the pattern appears to be a stable feature. Known to reach a size of 250 mm, it has been trawled from depths of 200 metres.( photo: Neville Coleman)
COMMON NAME: LINCK'S SEA STAR
SCIENTIFIC NAMES: Protoreaster lincki
12 metres, Mahe, Seychelles
Known from the Northern coastline of Western Australia this species occurs on sand, rubble and sea grass throughout the Indian Ocean. It has a very distinctive pattern of spines and can be easily separated from others of its genus. The species grows to 300 mm and feeds on detritus. As yet no associates have been recorded from its surface.( photo: Neville Coleman)
Sea stars have separate sexes (male and female) and although some (sand sea stars) actually participate in close contact external fertilisation, most just shed their reproductive products (egg and sperm) into the surrounding water at dusk during breeding season, or at night. Although large numbers of eggs are released, planktonic larval dispersal is often a risky process and few survive.
Some temperate water sea stars brood their young within their body, where they eventually emerge as juvenile sea stars. They can all regenerate damaged or missing parts and a few tropical species reproduce by deliberately breaking off an arm (autotomy) e.g. Linckia multifora and Echinaster luzonicus, or by breaking the body disc into unequal parts (fission) e.g. Allostichaster polyplax and Coscinasterias muricata.
COMMON NAME: SAORI SEA STAR
SCIENTIFIC NAMES: Nectria saoria
15 metres, West Island, South Australia
Discovered by pioneer scuba diver/ scientist Scoresby Shepherd this species was not described till 1967 and was named after the research vessel 'Saoria' from South Australia. It grows to 120 mm and ranges east into Victoria and west into South Western Australia. Colour may also be red or orange. Most of the few that I located were around the 20 metre depth.( photo: Neville Coleman)
COMMON NAME: NECKLACE SEA STAR
SCIENTIFIC NAMES: Fromia monilis
15 metres, Vila Vanuatu
Extremely variable in colour pattern and appearance and with several similar species known across the Indo Ð Pacific the Necklace Sea Star is not always easy to identify. However, in my book I have included all the colour variations I have come across which gives the largest range of the species ever published. This is one of the many species eaten by Harlequin Shrimps and one can tell that these shrimps are in the vicinity by observing sea stars with damaged or eaten arms. ( photo: Neville Coleman)
COMMON NAME: PINCUSHION SEA STAR
SCIENTIFIC NAMES: Culcita novaeguineae
10 metres, Milne Bay Papua New Guinea
Ranging from Japan across the Indo - Pacific, this inflated, rotund species can certainly be recognised to genus. It feeds on sponges, stony corals and detritus and may be found in any number of habitats from low tide level down to at least 92 metres. Size peaks at around 180 mm and the species is fairly common seen around coral reefs.( photo: Neville Coleman)
Many other animals live on sea stars including parasitic limpets (Thyca sp.), small eulimid molluscs (also parasitic), commensal scale worms, crabs, shrimps and creeping ctenophores.
Visual identification aided by location, habitat, shape, colour and pattern is possible on the majority of sea stars, but there are some which due to unavailable knowledge, lack of professional expertise, information and photographic comparison remain difficult and uncertain. Eventually, with books such as SEA STARS available for reference many of the unknown factors will become
These are but a few examples of Sea Stars which inhabit Australian and Indo – Pacific Seas, scuba divers have yet to discover just how extraordinary they are. Apart from their original descriptions little has been added through the 50 years that scuba diving has been in vogue. I wonder how much could be known if the diving community really related to their existence?
Copyright Neville Coleman