Chapter 2. Species Present
An initial study of the echinoderms of the Great Barrier Reef was conducted by H.L.Clark during a visit to the Murray Islands in 1913 (Clark, 1921). This work was followed by that of A.A.Livingstone during the Great Barrier Reef Expedition (Livingstone, 1932) and that of Gibbs, Clark and Clark (1976). Two monographs dealing with the Australian echinoderm fauna were compiled by H.L.Clark (Clark, 1938; 1946). Extensive biogeographical studies of Queensland echinoderms were undertaken by Endean (1953; 1956; 1957; 1961; 1965) and many of the records therein relate to Heron Island asteroids.
In the Indian Ocean, a detailed account of the echinoderm species present in West Australian waters was provided by Marsh (1976). Elsewhere in the Indian Ocean, the asteroid (starfish) fauna has been studied at Mozambique (Jangoux, 1972 a; Walenkamp, 1990), South Africa (Thandar, 1989), Somalia (Tortonese, 1980), the Gulf of Suez (James and Pearce, 1969), the Red Sea (Clark, 1967 a; Tortonese, 1960, 1977, 1979), the Arabian Gulf (Price, 1981), the Iranian Gulf (Mortensen, 1940), India (Koehler, 1910; James, 1973), the Andaman and Nicobar Islands (Julka and Das, 1978) and the Maldive Islands (Clark and Spencer-Davis, 1966; Jangoux and Aziz, 1985).
In the Pacific Ocean, the starfish fauna has been studied in China (Liao, 1980), Hong Kong (Clark, 1982), Taiwan (Chao and Chang, 1989), the Philippines (Fisher, 1919; Domantay, 1972; De Celis, 1980), the Ryukyu Islands (Hayashi, 1938 a), the Ogasawara Islands (Hayashi, 1938 b), the Caroline Islands (Hayashi, 1938 c; Grosenbaugh, 1981; Marsh, 1977; Oguro, 1984), the Mariana Islands (Yamaguchi, 1975 b; Kerr et al., 1992), the Marshall Islands (Clark, 1952), Indonesia (Guille and Jangoux, 1978; Jangoux, 1978), New Caledonia (Jangoux, 1984), Tonga (Clark, 1931), South East Polynesia (Marsh, 1974), Hawaii (Fisher, 1906; Ely, 1942) and the general North Pacific region (Fisher, 1911, 1925). The geographical distribution of the shallow water species was reviewed by Clark and Rowe (1971).
There have been many taxonomic revisions within the Asteroidea. The works of Baker and Marsh (1974), Blake (1979; 1980; 1981; 1983; 1990), Jangoux (1972 b; 1980), Pope and Rowe (1977), Rowe (1977) and Marsh (1991) have included species of coral-reef starfish. All previous revisions were summarised in the specific descriptions and keys to the asteroid species provided by Clark and Rowe (1971).
Specimens of several species of starfish were required primarily for size-frequency and reproductive analysis. Sampling methods were chosen so as to ensure that the sample sizes were sufficient to allow statistical analysis of size-frequency and reproductive data in a reasonable number of species. Starfish were collected by means of quadrats, general searches and on traverses that were conducted primarily at the western end of Heron Reef (Figure 1). On Heron Reef, traverses ran between the cay and the reef crest (0.5 to 2 kilometres apart) and also between two points both on the reef crest (0.5 to 6 kilometres apart). Because the primary purpose of sampling was the collection of size-frequency and reproductive data, the traverses were not stratified with respect to habitat. Traverses were neither systematic nor random and most traverses included both reef flat and reef crest zones. All exposed starfish within a four meter width were collected for the length of the traverse. In addition to the collection of exposed starfish, a selection of large and small, dead coral slabs were overturned and cryptic specimens located beneath these slabs were collected. The lagoon and its adjacent coral pools were not sampled by traverse because of the difficulty in traversing this habitat.
All traverses were conducted within two hours of low tide, during the period of spring tides (full or new moon). When the water over the reef flat and reef crest was any deeper than this or under adverse weather conditions it was difficult to locate smaller starfish. Specimens that were required for reproductive studies were collected during general searches at these times but these specimens were not included in either the abundance or size-frequency data because this would have been biased towards the more visible species and individuals.
In total, 72 overlapping, intertidal traverses were conducted during the period from May 1978 to December 1982. The total area sampled by these traverses was approximately 120 hectares (1.2 square kilometres) which is equivalent to about five percent of the shallow-water, reef area of Heron Reef. The mean traverse length was just over four kilometres.
Cryptic species were also sampled using metre square quadrats in particular areas where previous traverse sampling had shown that starfish abundance was relatively high. These samples provided data for starfish present on a very small area of the reef crest. These quadrat samples cannot be regarded as random and they are not typical of the reef crest in general. The reef crest zone is extremely variable and spatial heterogeneity (patchiness) appeared to be highly dependent on the scale of sampling. These quadrat samples were undertaken to obtain estimates of the starfish density in these localised patches.
Subtidal specimens of starfish were collected on the reef slope and off-reef floor by the use of SCUBA. These subtidal samples were not used to determine subtidal starfish density because limitations in underwater visibility would have resulted in the underestimation of all starfish abundances. Detailed quadrat sampling would not have been directly comparable with intertidal traverse data and such sampling was not considered appropriate given the logistical constraints of extensive sampling using SCUBA. The off-reef floor was only rarely sampled and the species that occur in this habitat may be much more abundant than is apparent from the results obtained.
All starfish were identified, measured and placed along with conspecifics in glass aquaria at the Heron Island Research Station. Specimens were identified by reference to Clark and Rowe (1971). Specimens were also compared with their original descriptions where necessary. An examination of the specimens with a stereoscopic microscope was sufficient to distinguish all species. Juvenile identification was possible in all cases by reference to Clark (1921), Yamaguchi and Lucas (1984) or Yamaguchi (1973 a, 1973 b, 1974, 1977 a).
All individuals not required for taxonomic study were released in habitats similar to those where they were found. Specimens of all species studied were photographed live and some were preserved in alcohol. These are housed in the Department of Zoology, University of Queensland.
Throughout this thesis, unless some ecological parameter is given higher priority temporarily, the sequence in which species appear in tables is determined by their systematic position. The families are sequenced according to Blake (1979, 1980, 1981, 1987, 1990) and the classification of Clark and Rowe (1971). The genera are sequenced alphabetically within families.
The species listed in Table 2.1 have either been recorded previously from Heron Reef, or were found in the present study and represent new records for the locality (marked with “*”). The species included are all those that occur either on the reef top (reef flat and reef crest) or on the reef slope extending to a depth of approximately 30 metres. At Heron Reef this is approximately the depth where the substrate of predominantly live coral or coral rubble changes to the finer sediments of the off-reef floor. Coral-reef species that do not appear to occur on the off-reef floor are marked “+”.
Table 2.1 Asteroid species recorded from Heron Reef.
Astropecten polyacanthus Muller and Troschel,1842
Iconaster longimanus (Mobius, 1859) *
Culcita novaeguineae Muller and Troschel,1842 +
Acanthaster planci (Linnaeus,1758) +
Asteropsis carinifera (Lamarck,1816) *+
Dactylosaster cylindricus (Lamarck,1816) *+
Fromia elegans Clark,1921 *+
Fromia milleporella (Lamarck,1816) +
Gomophia egyptiaca Gray,1840 +
Linckia guildingii Gray,1840 +
Linckia laevigata (Linnaeus,1758) +
Linckia multifora (Lamarck,1816) *+
Nardoa novaecaledoniae (Perrier,1875) +
Nardoa pauciforis (von Martens,1866) +
Nardoa rosea Clark,1921
Neoferdina cumingi (Gray,1840) +
Ophidiaster armatus Koehler,1910 *
Ophidiaster confertus Clark,1916
Ophidiaster granifer Lutken,1871 +
Ophidiaster lioderma Clark,1921 *+
Ophidiaster robillardi de Loriel,1885 *+
Ophidiaster watsoni (Livingstone,1936) +
Tamaria megaloplax (Bell,1884) *
Anseropoda rosacea (Lamarck,1816)
Asterina anomala Clark,1921 *+
Asterina burtoni Gray,1840 +
Disasterina abnormalis Perrier,1876 *+
Disasterina leptalacantha (Clark,1916) +
Tegulaster emburyi Livingstone,1933 *+
Mithrodia clavigera (Lamarck,1816) *+
Echinaster luzonicus (Gray,1840) +
Echinaster stereosomus Fisher,1913 *
Coscinasterias calamaria (Gray,1840) *
* new record for Heron Reef + coral-reef species
In addition to the preceding species, Anthenea aspera, Stellaster equestris, Metrodira subulata and Acanthaster brevispinus were recorded from the area by Bennett (1958). These species were dredged from a depth of 45 meters east of Wistari Reef and were not directly associated with any coral-reef habitat. Halityle regularis was recorded by Baker and Marsh (1974) and Andora popei was recorded by Rowe (1977) from the off-reef floor near Heron Reef. Pentaceraster regulus and Euretaster insignis were also observed on the off-reef floor.
The following brief notes relate to the species of starfish that have been located at Heron Reef (on the reef flat, reef crest or reef slope) either in this study or by previous workers.
Astropecten polyacanthus Muller and Troschel,1842
This species of starfish is not restricted to coral reefs, but occurs also in sandy areas along the east coast of the Australian mainland. It was not common but specimens were found during this study in the deeper waters of the off-reef floor. It is recognised by the many conspicuous sharp spines along the body margin. The tube feet do not possess suckers at their tips. It has been found on a sandy spit at Heron Island Reef by Endean (1965).
Iconaster longimanus (Mobius,1859)
This orange and white patterned starfish is immediately recognised by its long tapering arms. It was not common at either Heron or the adjacent Wistari Reef, but specimens were located during this study in about 20 metres of water on the deeper parts of the reef slope. They were usually associated with coral rubble. Some specimens that were collected had recently lost one arm.
Culcita novaeguineae Muller and Troschel,1842
The juveniles of this species (R less than 70 mm) look quite different from adults. This starfish is most commonly encountered on the reef flat although it occurs also on the reef crest. Its greatest abundance may be at the base of the reef slope or in the deeper coral pools adjacent to the lagoon. This large and conspicuous species was not common on the traverses at Heron Reef during the period of this study.
Acanthaster planci (Linnaeus,1758)
This well known species was uncommon at Heron and the adjacent Wistari Reef during the period of the present study. Only five subtidal adults and one juvenile specimen were encountered. Endean (1961) recorded a single specimen from a pool near the reef crest at Heron Reef.
Asteropsis carinifera (Lamarck,1816)
This species is not common at the southern end of the Great Barrier Reef. It has been recorded as common at Mer in the Murray Islands (Clark, 1921). During this study, three specimens were encountered on the reef crest at Heron Reef.
Dactylosaster cylindricus (Lamarck,1816)
During this study, a single specimen was located on the reef crest at Heron Reef. Few specimens of this species have been found on the Great Barrier Reef or elsewhere throughout its range. This species can be distinguished from others in this family by the presence of only a few small granules in the centre of each plate of the body. The remaining granules are concealed by a skin-like membrane. It occurs on the rocky reefs off southern Queensland more frequently than it does at Heron Reef.
Fromia milleporella (Lamarck,1816)
One specimen was found on the reef crest. Endean (1956) found two specimens under boulders on the reef crest.
Fromia elegans Clark,1921
At Heron Reef, this starfish is relatively common in the reef slope zone. Most specimens have five even arms, but specimens with four and six arms were not uncommon. This species was found also on the reef crest lying exposed in small pools, and on the sand at the base of the reef slope in 20 metres of water.
Gomophia egyptiaca Gray,1840
At Heron Reef, the only individuals encountered, during this study, were coloured purple and brown with pink tips to the tubercles which cover the aboral surface of the body. Specimens of this species were usually found either concealed under boulders on the reef crest or crawling amongst dead coral rubble on the reef slope. This species is not common at Heron Reef. Of the small number of intertidal specimens collected, two were found in close proximity. Endean (1965) found only two specimens on the reef flat at Heron Reef.
Linckia guildingii Gray,1840
The Grey Linckia, while not as common as L. laevigata or L. multifora, is encountered frequently on reefs of the Great Barrier Reef. The grey coloration conceals the animal when crawling over dead coral clumps which are covered by filamentous algae, but the animal is conspicuous when on coral sand. Although the adult starfish is uniform grey in colour, juveniles are mottled white, grey and purple, and do not lose this appearance until a size of about 80 mm arm radius is attained.
Linckia laevigata (Linnaeus,1758)
The Blue Linckia inhabits intertidal reef areas throughout the Indo-West Pacific region. It attains a large size (arm radius 180 mm), is brightly coloured, and is usually found lying unconcealed on or near coral clumps in the reef flat. It can be found also on the reef crest, lying either exposed on the algal rim or partially hidden under coral boulders in the rubble zone. There is very little colour variation within this species on the Great Barrier Reef. The most frequent number of arms is five although arm number ranges from three to seven. The extremes are rare.
Linckia multifora (Lamarck,1816)
This species is usually found with one or more arms missing, these having been autotomised. The maximum size that this animal attains at Heron Reef is about 100 mm arm radius, but most specimens are approximately one-third this size. Sometimes the starfish will be found crawling in the open across the reef crest but more often it will be found under boulders. The specimens which occur under boulders are usually smaller and lighter in colour and do not have the brown coloration which is found in those that have adopted an exposed existence. The most common number of arms is six but the number varies between three and eight. It is unusual to find a specimen with all arms of equal length.
Occasionally specimens are found that do not belong clearly to either Linckia laevigata or Linckia multifora. These specimens are blue in colour but have pointed arms and show evidence of recent autotomous reproduction. There is a small row of granules between the furrow spines. One blue comet form has been found during this study. Because of their general morphology, these specimens have not been regarded as Linckia laevigata, but as colour variations of Linckia multifora.
Nardoa novaecaledoniae (Perrier,1875)
The two common species of Nardoa appear quite similar in overall appearance and differ in the arrangement of the plates which cover the arms. In Nardoa novaecaledoniae these plates are abruptly reduced in size in the outer one-third of each arm.
Nardoa pauciforis (von Martens,1866)
This starfish is slightly less common than the previous species but is not hard to find on Heron Reef. It occurs more commonly on the reef flat than on the reef crest but it can be overlooked in this habitat as both N. pauciforis and N. novaecaledoniae blend well with the background of living and dead coral. The animals are most conspicuous when crawling over the sand between coral clumps. The average individual size of this species is slightly larger than that of N. novaecaledoniae. Also, the arms are usually longer relative to the body than in N. novaecaledoniae. A diagnostic feature of N. pauciforis is the absence of an abrupt change in the size of the plates towards the outer one-third of the arms.
Nardoa rosea Clark,1921
This species is more frequently encountered in the deeper parts of the reef slope (20 meters) than on the top of the reef at Heron Reef, but is not common in any of these habitats. It is a beautiful starfish with an average size of 90 mm arm radius.
Neoferdina cumingi (Gray,1840)
This starfish is not encountered often on the reef top at Heron Reef, but is occasionally seen when diving on the reef slope. There is great variation in the number and pattern of the red spots which are conspicuous along the arms.
Ophidiaster armatus Koehler,1910
All members of the genus Ophidiaster possess four rows of papular areas on both sides of every arm, a total of eight rows per arm. Papulae are the respiratory organs and occur in groups of between five and twenty, each appearing as a small, transparent projection through the outside body wall. The extent to which each papula is extended is dependent greatly on the water conditions.
O. armatus is readily recognisable by its dark coloration, tapering arms and by the coarse feel of the animal due to the very rough granulation of its skin. This species is found in low numbers, mainly at the base of the reef slope at Heron Reef.
Ophidiaster granifer Lutken,1871
This species possesses the tapering arms and uneven granulation of the previous species, but it is easily distinguished by its general coloration, smaller size (25 mm) and shorter arms relative to the diameter of the disc. Specimens of this species are usually encountered under boulders on the reef crest where they occur with moderate abundance. They are always cryptic in their habits.
Ophidiaster lioderma Clark,1921
This moderate sized starfish (R=100 mm) is very rare indeed having been found on two known occasions only, in two localities which are far apart on the Great Barrier Reef. The original specimen was discovered by H.L.Clark when he visited the northern end of the reef and was based at Murray Island in Torres Strait at the turn of the century. During this study, a further specimen was located on the reef crest at Heron Reef and is now housed in the West Australian Museum.
This species is a medium-brown in colour and can be readily identified by the skin covered body which possesses microscopic granulation. The only other member of this family which has a covering of thick skin is Leiaster leachi but this species has no surface granulation whatsoever and is brightly coloured.
Ophidiaster confertus Clark,1916
Four specimens of this species were located on the reef crest at Heron Reef. This species which grows up to 160 mm arm radius occurs more commonly on the New South Wales coast than at the southern end of the Great Barrier Reef (Clark, 1946).
Ophidiaster robillardi de Loriel,1885
This species occurs in moderate abundance in patches at Heron Island. The extreme patchiness of the distribution and abundance of this species is attributable to low dispersion associated with asexual reproduction. The average size of specimens is 35 mm arm radius and about ten percent of the specimens encountered were comet forms resulting from autotomous reproduction.
Ophidiaster watsoni Livingstone,1936
Gomophia egyptiaca and Ophidiaster watsoni are very similar and may be conspecific. Endean (1956) found one specimen of O. watsoni under a boulder on the reef edge at Heron Island.
Tamaria megaloplax (Bell,1884)
This species is found in the deeper waters, on sand near the base of the reef slope at Heron Reef. It occurs much more commonly on rocky reefs in south-east Queensland, than it does on the Great Barrier Reef. The average size of specimens found in south-east Queensland is about 100 mm arm radius. The specimens show considerable variation in the degree of roundness of the plates on the arms. This genus is characterised by having only three parallel rows of papular groups on both side of each arm, unlike Ophidiaster which has four, and Hacelia which has five rows.
Anseropoda rosacea (Lamarck, 1816)
A single specimen of this species was found on sand in a reef-crest pool at Heron Reef by Endean (1956).
Asterina anomala Clark,1921
This small starfish is usually hard to find as the maximum size of individuals found on the Great Barrier Reef is about 5 mm arm radius. The bright coloration is of little help in finding this species as the boulders under which it occurs are encrusted usually with other brightly coloured invertebrates such as sponges and ascidians. This species is probably much more common than it appears to be but its small size makes sampling extremely difficult.
The usual number of arms in this species is seven. Half of these are normally regenerating as this species reproduces by binary fission. In this process, the animal divides into two and both sides regenerate the missing arms. If the regeneration has not proceeded very far then three or four adjacent ambulacral grooves will not extend much beyond the mouth.
Asterina burtoni Gray,1840
The taxonomic positions of this and of the preceding species are not clear. While the coloration of Asterina burtoni is quite variable, ranging from grey, through green to red or purple, it does not exhibit the multi-coloured pattern possessed by the previous species. A. burtoni does not reproduce by fission at Heron Reef and consequently most specimens have five arms of equal length. The average size of specimens is 13 mm arm radius.
Disasterina abnormalis Perrier,1876
This species has been recorded at a few localities along the Great Barrier Reef, and also in Indonesia as well as in the South Pacific. When alive, the animal is covered by a relatively thick skin which conceals the underlying plates. Many of these plates bear some very short rounded spines but it is not possible to discern the diagnostic characters of this species unless the specimen is preserved and then dried.
At Heron Reef at the southern end of The Great Barrier Reef, this is the most abundant starfish found on the top of the reef. It lives amongst the broken coral rubble on the innermost portion of the reef crest. The average size of specimens is 15 mm arm radius, but this size varies with periods of growth and with recruitment of juveniles to the population.
Disasterina leptalacantha (Clark,1916)
This close relative of the preceding species grows to the same size, but is known only from the Capricorn Group at the southern end of the Great Barrier Reef. The difference between these two species is unmistakable as Disasterina leptalacantha possesses very long, extremely thin spines along the body margin, but in life these may be folded upwards against the side of the body and are overlooked easily. The coloration of this species is different from that of the previous one and the arms are also slightly longer. The reason for the apparent limited distribution of this species is unknown.
The main habitat of this species is amongst the broken slabs of beachrock at low tide level. It is not common but specimens will be found either adhering to the underside of the rocks or amongst the sand immediately under the rocks.
Tegulaster emburyi Livingstone,1933
During this study, one specimen of this species was located on the reef crest at Heron Reef. The only other known specimen of this species was found at North-West Island, also in the Capricorn Group. Both specimens were found under a dead coral boulder in the reef crest zone. This species is exceedingly rare and may also be highly restricted in its geographic range. Both known specimens were just under 20 mm in arm radius.
Mithrodia clavigera (Lamarck,1816)
During this study, one specimen was located at Heron Reef, but it did not occur within the intertidal traverses. It was located on the reef crest in December 1984. The species has been found elsewhere in the South Pacific but is uncommon.
Echinaster luzonicus (Gray,1840)
This starfish ranges from almost black, through red, to speckled orange and black in coloration. Specimens with all arms of equal length are not common as this species reproduces by means of autotomy, and comet forms will be found along with the adults in most habitats. The habitat in which this species is most abundant is under coral boulders on the reef crest. However, specimens may be found in most other intertidal habitats as well as on the reef slope and extending down to the boundary with the off-reef floor. The specimens which are found sub-tidally are larger usually than those found intertidally. The average size of specimens varies from one reef zone to another, but on the reef crest it is about 47 mm arm radius. However, its size is dependent on the amount of autotomy which has occurred recently. The species can grow to about 90 mm. Some of the specimens encountered at the edge of the off-reef floor possess epiphytic ctenophores crawling over the arms of the starfish.
Echinaster stereosomus Fisher,1913
At Heron Reef, this species is found near the base of the reef slope. It occurs on the rocky reefs off southern Queensland more frequently than it does at Heron Reef.
Coscinasterias calamaria (Gray,1840)
This is primarily a southern species (Clark, 1946). Barrier Reef specimens are small, up to 30 mm arm radius, compared with the much larger individuals found on the mainland coast. This species is capable of asexual reproduction by binary fission. At Heron Reef, C. calamaria maintains small patches of moderate abundance by asexual reproduction. Indeed, it appears unlikely that specimens grow sufficiently large to become sexually mature at Heron Reef.
The following species represent new records for Heron Reef:
Iconaster longimanus, Asteropsis carinifera, Dactylosaster cylindricus, Fromia elegans, Linckia multifora, Ophidiaster armatus, Ophidiaster lioderma, Ophidiaster robillardi, Tamaria megaloplax, Asterina anomala, Disasterina abnormalis, Tegulaster emburyi, Mithrodia clavigera, Echinaster stereosomus and Coscinasterias calamaria.
This study has provided the most southerly records from Great Barrier Reef waters of Iconaster longimanus, Asteropsis carinifera, Dactylosaster cylindricus, Fromia elegans, Linckia multifora, Ophidiaster armatus, Ophidiaster lioderma, Ophidiaster robillardi, Tamaria megaloplax, Asterina anomala, Disasterina abnormalis, Mithrodia clavigera and Echinaster stereosomus.
Single specimens of both Ophidiaster lioderma and Tegulaster emburyi were recorded at Heron Reef during this study and these represent the only known specimens of these species apart from their holotypes. Additionally, this study has provided the first record of the predominantly temperate species, Coscinasterias calamaria on the Great Barrier Reef. Euretaster insignis, which has not been recorded in the vicinity of a reef of the Great Barrier Reef, was found on the off-reef floor between Heron and Wistari Reefs.
Ophidiaster watsoni and Anseropoda rosacea were recorded from Heron Reef by Endean (1957) but were not located during this study. The taxonomic position of the former species is unclear. Anseropoda rosacea either is very uncommon at present, or primarily inhabits the sandy bottom of the lagoon which was not sampled extensively. Ophidiaster hemprichi and Ophidiaster lorioli occur at Heron Reef (Marsh pers. com.), but were not located during this study. Halityle regularis and Andora popei have been recorded from the off-reef floor in the vicinity of Heron Reef, by Baker and Marsh (1974) and Rowe (1977) respectively. These species were not located during this study as the off-reef floor was not sampled as intensively as were the shallow-water zones.
Because of its southerly position on the Great Barrier Reef, some predominantly sub-tropical asteroid species (e.g. Ophidiaster confertus and Coscinasterias calamaria) occur at Heron Reef but appear to not occur further north on the Great Barrier Reef. Additionally, some predominantly mainland species (Endean, 1957) occur either on, or in close proximity to, reefs of the Great Barrier Reef. The biogeographical study of Endean (1957) has shown that a distinction must be made between the asteroid species which occur predominantly on coral reefs of the Great Barrier Reef and those which occur elsewhere in Queensland waters. The results of the present study are in accord with this view. Clearly, there is a coral-reef asteroid fauna exemplified by that of Heron Reef, which is different from that of off-reef waters. However, as noted by Endean (1957), some species which occur on reefs of the Great Barrier Reef are not exclusively coral-reef species. For example, species such as Archaster typicus, Protoreaster nodosus, Ophidiaster confertus, Tamaria megaloplax, Asterina nuda, Patiriella pseudoexigua, Anseropoda rosacea and Coscinasterias calamaria occur predominantly in habitats other than those provided by coral reefs.
It seems likely, because of the extremely southern position of Heron Reef and other reefs in the Capricorn and Bunker Group, that many of the predominantly coral-reef species do not occur there with the same abundance as they do further north where physical conditions such as low water temperature on the reef flat in winter may be less extreme. Additionally, the relative isolation of this group of islands and reefs from the rest of the Great Barrier Reef might influence the abundance of those species with a low capacity for larval dispersal. However, these factors do not appear to affect the abundance of species that are common throughout the Great Barrier Reef. At higher latitudes, such as that of Heron Reef, the factors just mentioned might increase the abundance range between the most common and the rarest species. This would be reflected in the extent of sampling that would be required to locate most of the species that occur in the locality.
When current asteroid species lists for Heron Island and other reefs of the Capricorn Group are compared with those of recent studies of the North Pacific coral-reef Asteroidea (Yamaguchi, 1975 b; Marsh, 1977) it is apparent that some of the species that occur at Guam or Palau (e.g. Archaster typicus, Celerina heffernani, Fromia indica, Fromia monilis, Nardoa tuberculata, Nardoa tumulosa, Neoferdina offreti, Asterina corallicola and Echinaster callosus), have not been recorded from the Capricorn Group. On the other hand, some of the species that have been recorded from Heron Island and other reefs of the Capricorn Group (e.g. Tosia queenslandensis, Iconaster longimanus, Fromia elegans, Nardoa pauciforis, Nardoa rosea, Neoferdina cumingi, Ophidiaster armatus, Ophidiaster lioderma, Disasterina abnormalis, Disasterina leptalacantha and Tegulaster emburyi), have not been recorded from either Guam or Palau.
Future investigations may reveal that some of the above similar but geographically separated coral-reef species (e.g. Fromia indica and Fromia elegans) are conspecific. However, future investigations may also confirm the restricted distributions of some of the species mentioned above.
Most of the coral-reef asteroids found on the Great Barrier Reef, including Heron Reef and other reefs of the Capricorn Group, have strong affinities with coral-reef asteroids of the Western Pacific region as noted by Endean (1957). However, a few species appear endemic to the reefs of the Capricorn Group or are essentially sub-tropical species that have extended their ranges to include the southernmost reefs of the Great Barrier Reef.