Sandmining, Monazite and Xenotime: Radiometric Unfiltered Thorium and Uranium ppm Images – 2015

It was 1975 when Sinclair v Maryborough Mining Warden changed the future of  our beaches and mineral sand mining forever. High Court Chief Justice Sir Garfield Barwick together with Justices Gibbs, Stephen, Jacobs and Murphy made their feelings about the lawfulness of mineral sand mining decisions by the Queensland Government very clear.

“5. In conclusion I would, with respect, adopt what was said by Lucas J. in the Supreme Court, that the courts are not concerned with the question of the desirability of permitting sand mining to take place or with the question whether the recommendation of a warden is right or wrong, provided that he has performed the duty cast on him by the law. In the present case the warden failed to perform his duty and should therefore now be directed to proceed with the hearing in accordance with the provisions of the regulations. (at p483)”

Cooloola_Cove_GoogleFrom Cooloola, Dunwich, Gold Coast and Currumbin in Queensland to Byron Bay, Mooball, Woodburn, Jerusalem Creek and others in New South Wales, mineral sands were mined, concentrated and stockpiled. Because mines varied in their mineral composition and miners targeted different minerals over the decades, both monazite (thorium), xenotime (uranium) and other minerals were returned to particular areas of the mineral sands operation and other sites as waste. Some of this material was even used as public and private land fill. These places where mineral sand waste was stockpiled or buried during late-19th and 20th century sandmining operations are visible today in Radiometric imagery.

Cooloola Cove (QLD)


As stated in an article by Byron Bay Historical Society:

“Much concern accompanied the disposal of ‘radioactive waste’ from the processing plant. This radioactivity was caused by monazite, a thorium-bearing, resistive, heavy mineral contained in the black sand concentrated from the beaches. In the early years after WWII the Australian Federal Government mandated that this mineral be recovered and stored by the sand miners as thorium was a potential fuel for nuclear power generating stations. Ultimately uranium became the preferred fuel and most mineral sand producers were left to dispose of any monazite they could not sell. Sand miners either mixed it with normal sand and buried it or returned it to the beach whence it came.”

Brisbane and Dunwich (North Stradbroke Island, QLD)


Gold Coast QLD)


Currumbin (QLD)


Byron Bay (NSW)


Mooball (NSW)


Woodburn (NSW)


Jerusalem Creek


This is quoted from NSW National Parks and applies from Tue 18 Jul 2017, 7.00am to Tue 30 Jun 2020, 5.00pm. Last reviewed: Tue 15 Aug 2017, 1.12pm

“Safety alerts: Ilmenite stockpile removal and site rehabilitation

Visitors to Black Rocks campground should expect to encounter large trucks on The Gap Road. This is part of a major project to remove a sand mining tailings stockpile from the park and restore the area to a natural ecosystem. Park visitors are asked to slow down and exercise caution while driving along The Gap Road. No works associated with this project will be undertaken on weekends, public holidays or NSW school holidays. The truck movements are expected to continue until June 2020. For more information or to report any incidents please contact the NPWS Richmond River area office on (02) 6627 0200.”

CoTS and Code of Ethics for Researchers


“Engaging with decision-makers means going beyond developing solutions, conducting experiments and publishing data. Situations arise in which there is an ethical responsibility to engage with decision-makers, be they representatives of government, academia, companies or other entities – for instance to correct health misinformation around vaccination safety or to understand the impact of climate change on populations. Other situations exist in which research is only possible by engaging with decisionmakers – for example to access government or corporate data sets, facilities or resources. This engagement may be at any or all stages of the research process as needed. Reasons to engage are manifold, but ultimately the involvement of decision-makers greatly facilitates the probability that scientific outcomes will be translated into positive societal change.”

Introduction to initial thesis of 1985 (without revision)

The primary hindrance to any creative synthesis is the failure to recognize the causes of dissension in science. In some cases a critic may doubt the integrity of either the scientist or the data. In these cases further repetition of experiments may alleviate skepticism. In other cases, there may be a philosophical disagreement which has its basis in differing beliefs held by scientists. These preconceptions, which all scientists possess, can severely limit the process of conciliation. Dissension, however caused, is not easily resolved, and often leads to polarization within science. The failure of science to recognize and acknowledge explicitly, the validity of differing viewpoints based on the same data demonstrates confusion over these two causes of dissension.

Additionally, our aversion to implausible conjecture has limited the diversity of models that can be open to empiric testing. It must be remembered that, when seen through the eyes of a different culture, a model held to be true universally might appear implausible. An example is our astonishment at the complexity of Micronesian fishhooks which have been individually crafted to capture specific types of fish (Johannes, 1981). The pattern of relative planetary movements in our solar system was simplified greatly when the geo-centric model was discarded, in favor of a model in which the planets moved in orbits about the sun (Whitlam, 1975). This and other conceptual leaps have occurred when cultural limitations were waived temporarily, and the consequently greater insight justified the cultural changes that followed. The phrase, “that is only conjecture”, seems to imply that many scientists regard conjecture as superfluous in the day to day running of science. In the pursuit of scientific rigor, we often overlook this necessary component of synthesis and find it increasingly difficult to model our thoughts in a manner that enables others to see a more distant horizon by standing on our shoulders.

Finally, the scientific process might not progress beyond the accumulation of facts. Often it appears impossible, from the data, to do more than simplify nature’s variability by statistics, to categorize its variety by description or to model its behavior mathematically. These techniques should be tools to further understanding of the interrelationships between the elements under study. To many workers the apparently stochastic nature of many phenomena prohibits a more detailed analysis.

In recent years there have been many studies in coral reef ecology, biology and biogeography. Often, they are related, one to another, by a common principle or factor (e.g. population outbreaks of Acanthaster planci, plans for reef management or theoretical questions about the causes of diversity). Whenever several independent researchers study similar phenomena or ask similar questions, the possibility of dissension arises. The ensuing debates, and even hostility, can appear as a failure in communication between the scientists concerned. More often the observed behavior results from philosophic disagreement taking its natural course. Philosophic changes in both science and society are often inseparable; they rarely occur, figuratively speaking, without bloodshed.

Philosophic clashes are likely to occur whenever the capacity to acquire data, strategic to the opposing viewpoints, approaches a limit imposed by logistics or technology. This is certainly the case with much of the ecological debate over population outbreaks of Acanthaster planci. The failure to recognize the symptoms of this fundamental disagreement can lead to much wasted effort, funds and, most of all, time. Often, we need to determine which observations are required to swing general support from one model to another. However, the competing models may have reached the same level of logistic untestability and there may be no logistically possible observation or series of experiments which could distinguish between the validities of either model.

There has been much debate about the relative roles of disturbance, stability and niche specialization, as factors contributing to the co- existence of the large number of species in some communities (e.g. Brown, 1981; Connell, 1978; Levins, 1963; MacArthur, 1955, 1969; May, 1972, 1974; Paine, 1966). By contrast, there has been little consideration of the possibility that these factors and associated models may be of secondary importance to community order or structure itself. The process of community succession follows a path of increasing complexity towards an hypothesized relatively static, climax community, the composition of which is determined by prevailing environmental as well as historical parameters (e.g. Dunbar, 1972). Throughout this process, as early (rapid) colonists are excluded by species that are competitively superior, the composition of the community changes. The number of species present in the community increases to a maximum at some stage of succession, prior to the climax and subsequently decreases as a result of the exclusion of inferior competitors (Connell, 1978). The extent to which disturbance, by creating spatial and temporal patches of early succession, acts to prevent the monopolization of available resources by a small number of superior competitors has been discussed extensively (e.g. Dayton, 1971; Levin and Paine, 1974). Other authors have either proposed or implied that high diversity communities are at equilibrium, and that species coexistence is mediated by the complex processes of interdependence and specialization that have evolved, in a physically benign environment, over long periods (e.g. Fischer, 1960; Sanders, 1969; and reviews by Goodman, 1975; Osman and Whitlatch, 1978; Pianka, 1966). Additionally, Jacobs (1974) and Peters (1976) have pointed out that the correspondence between stability in species composition and stage of community succession is tautological because a successional climax is defined in terms of its temporal stability.

The progressive increase in diversity, biomass, complexity and structure, resulting from the succession process, has been the focus of much discussion (e.g. Dunbar, 1972; Margalef, 1963; Odum,1969). In some instances (e.g. Sale, 1984), the co-existence of numerous species can be explained without resorting to complex, pattern oriented, models that require numerous assumptions which are testable only by prolonged, rigorous and exacting field observation. The almost universally accepted null hypothesis of “chance” does very little to enlighten biological scientists who want to understand or observe any existing inter-relationships between the species they study; that hypothesis, however, has gained a reverence totally unbecoming a statement that claims to say nothing at all (Dunbar, 1980; Roughgarden, 1983).

Any function which may be played by community order or structure has, in the past, been so secondary to the aims or objectives of the “experimental approach”, as to be uninteresting or considered logistically untestable (i.e. impractical or too difficult). However, there is a fundamental difference between a model being logistically untestable and it being logically untestable (for discussion compare Connell, 1980; Dunbar, 1980; Kuhn, 1970; Popper, 1983; Quinn and Dunham, 1983; Roughgarden, 1983; Simberloff, 1982). I do not propose that all the myths laid to rest by “Occam’s Razor” be resurrected and considered as reasonable explanations of available evidence. However, I do suggest that, in the field of coral reef ecology, our attempts to simplify the system under study have produced models that bear little relationship to reality. The rigid adherence to the least complex and ramifying hypothesis, has made it difficult to see beyond the generally accepted view of nature based on probability theory and chance

While there have been many taxonomic and biogeographic works dealing with the coral reef asteroid community (Clark, 1921, 1938, 1946; Clark and Rowe, 1971; Marsh, 1974; Marsh, 1974, 1976, 1977; Yamaguchi, 1975b), the ecological requirements of asteroid species occurring within the Indo-West Pacific region have not been studied extensively. It is known that many species occur on coral reefs throughout the region (Clark and Rowe, 1971), while others possess a more restricted distribution. Several asteroid species are known from only a few specimens and are considered to be rare (Clark, 1921; Yamaguchi, 1975b). The habitat requirements of coral reef asteroid species, and the ecological roles of rare as well as of more common species are not understood. It is not known whether rarity is a survival strategy, an abundance limit imposed by predators or a failure in competitive ability of a species on its path to extinction. These questions have not been answered for this or any other taxonomic group within the highly diverse and complex ecosystem of the coral reef.

Competition and other ecological models and corollaries draw their scientific context often, by analogy, from the corresponding pattern of interaction observed within contemporary human society. The influence of one’s cultural background in the initial perception and subsequent acceptance of the ecological generality of these analogies is overlooked often. A model is an abstraction only, but in common with all scientific models, socially analogous models can be raised, by consensus, to the status of paradigms, such that, observations which contradict the model are considered either inaccurate or implausible. Assume that the population size of some organism is limited by the level of juvenile recruitment in such a way that the density of adults is never sufficiently high for one individual to interact significantly with another (e.g. Dale, 1978; Doherty, 1982). If these assumptions were true but unknown, the interactions between adults and their ecological significance could be modeled incorrectly using competition theory. Observations, which are categorized within a severely limited body of theory, cannot be regarded as empiric support for any hypothesis, as biased observations can provide support for any model. It is possible that many organisms live presently at adult population densities, which are sufficiently low to preclude both, inter and intra-specific competition. In such species, the adult population density may be limited always, at some previous stage of the life cycle, and the adult populations may be free from density dependent interactions.

A range of reproductive strategies is found in coral reef asteroids. Sexual recruitment can follow either planktotrophic or lecithotrophic larval development (Yamaguchi, 1977b). The occurrence of parthenogenetic development (Yamaguchi and Lucas, 1984), hermaphroditism (Achituv, 1972) or asexual reproduction (Rideout, 1978) may be correlated with survival at low population density and the consequential low probability of locating an opposite sexed conspecific at breeding time. Within coral reef asteroids, asexual reproduction has been observed in Linckia guildingii, Linckia multifora, Ophidiaster robillardi, Echinaster luzonicus and Asterina anomala (Emson and Wilkie, 1980). This provides evidence that, in some species under certain conditions, genetic variability and potential dispersal are less important to the maintenance of population numbers, than is continuity of recruitment.

The larvae of coral reef asteroids generally require a solid substrate to complete their development, and a coralline algal substrate has been observed as the chosen settling surface for many species (Yamaguchi, 1973b). More complex species-specific optima, located by sensitive chemo-sensory receptors might ensure settlement in habitats which are conducive to survival of post-settlement stages (Morse, 1984). Yamaguchi (1977c) showed that some juvenile asteroids have exponential growth during the period following settlement and proposed that juveniles are subject to high mortality during this period. The juveniles transform to adult morphology at a certain size and before this may look quite different from adults (e.g. Culcita novaeguineae illustrated by Clark, 1921).

A general paucity of information about juveniles characterizes available data on population structures of large bodied, coral-reef asteroids (Yamaguchi, 1973a). It is possible that populations are maintained either by continual low recruitment or occasional high recruitment, each coupled with iteroparity. The juveniles are cryptic and their apparent absence or rarity indicates that reproductive success is either constantly low, sporadic or both. Sporadic success may depend on factors such as availability of planktonic food, level of planktonic predation or mortality of settled larvae. These may average out over the life span of the adult resulting in stability of adult numbers. Population increases of coral reef asteroid species have been well documented for Acanthaster planci, and apparent population increases of Linckia laevigata following Acanthaster outbreaks have been described (Laxton, 1974).

The differing requirements for growth and successful recruitment of juveniles, within the coral reef asteroid community, will have resulted in diverse life history strategies. A conceptual dichotomy exists in our perception of the life history of all organisms, and is referred to as r- versus K- strategy (Pianka, 1972; Stearns, 1976). These different survival characteristics are thought to have evolved in response to specific types of environments (Hairston, Tinkle and Wilbur, 1970; Murphy, 1968; Wilbur, Tinkle and Collins, 1974). The spectrum of existing life history attributes, apparent in any community study (see e.g. Menge, 1975; Vance, 1973), represents many points on a continuum between the conceptually ideal r- strategists and K- strategists.

Goodman (1974) proposed that if a population’s size is limited mainly by competition then natural selection will result in an increased competitive ability (K-selection) and, in populations which are not resource limited, selection will result in an increased reproductive rate (r-selection). The reproductive effort (energy used for reproduction compared with the energy used for non-reproductive purposes) and age specific mortality schedule are an indication of the type of selection which has occurred during the evolution of a species (Pianka, 1972).

The longevity of a species is determined by the relative probability of juvenile and adult survivorship. In the simplest case, if the probability of a sexually mature organism’s survival from one reproductive season to the next is greater than the probability of one of the offspring reaching sexual maturity, then the species will exhibit iteroparity (see Goodman, 1974; Murphy, 1968). The weighting of selective attributes is arbitrary (e.g. niche specialization, number and size of eggs, longevity, possession of toxin), as the absolute ends of the r-K continuum do not exist in reality. Unpredictable environmental factors (e.g. perils of larval life and enormous potential dispersion) can result in a high numerical fecundity, and consequentially, most marine benthic invertebrates have a high energy cost associated with reproduction (Mileikovsky, 1971).

The dispersal stage of a population spreads the risk of local extinction in space and time (den Boer, 1968; Scheltema, 1971; Strathmann, 1974). The early stages of succession survive by being able to colonize regions quickly following disturbance. The resultant spatial and temporal variation in population size seems to characterize the typical r- strategists. Their populations are stable only when viewed on a larger scale. The spatial and temporal scale at which a species must be viewed for its numbers to be stable is an indication of its position on the r-K continuum.

The life history strategy, of each species, will be viewed in this context and a variety of strategies should be observed within the coral reef asteroid community. Early succession species would be expected to have large fluctuations while late succession species should have smaller ones. Stable, climax communities should be characterized by small fluctuations of their component species. The apparent stability of any biological system is dependent on the scale of observation (see Bradbury and Reichelt, 1982; Sale, 1984; Weiss, 1969). At the organismic scale, there would be neither temporal nor spatial abundance variation if an individual exactly replaced itself, without dispersing, then died. At the population scale, a level of numerical stability, consistent with a model of community equilibrium and climax, could be achieved if dispersion, larval survival and settlement phenomena did not result in greatly differing adult numbers from one year to the next.

Since the late 1950’s, coral reefs of the Indo-West Pacific region have experienced population outbreaks of the corallivorous asteroid Acanthaster planci (e.g. Bligh and Bligh, 1971; Branham, 1973; Chesher, 1969; Endean and Chesher, 1973; Endean and Stablum, 1975; Goreau, 1963; Heydorn, 1972; Kenchington, 1976; Marsh and Tsuda, 1973; Pearson, 1972). The resultant loss of hard coral cover on some reefs of the Great Barrier Reef was studied during the period of outbreak, and subsequently, so that both the short and long term effects of this predator would be known (Endean and Stablum, 1973; Pearson, 1981). The role of this predator in the elevation or lowering of coral species diversity on the Great Barrier Reef has not been studied adequately. It is apparent that some reefs become reinfested with Acanthaster planci about 15 years following the initial infestation (Cameron and Endean, 1982). It would appear, that when the quantity (not necessarily diversity) of a reef’s hard coral cover has regrown, the asteroid can recruit again in high numbers.

Although the Acanthaster planci population outbreak phenomenon has puzzled scientists for a quarter of a century, and although many explanatory hypotheses and models have been proposed (e.g. Birkeland, 1982; Endean, 1969; Flanigan and Lamberts, 1981; Randall, 1972; Sale, Potts and Frankel, 1976), there remains disagreement about the causes of the phenomenon. Additionally, there is disagreement about the need for reef management strategies that might mitigate the widespread effects of this coral predator. The extent of present population outbreaks and the possibility of past outbreaks (prior to 1960) have not been studied in sufficient detail to allow critical evaluation of either the problem itself, or the risks associated with incorrect management. We do not know what factors allow high recruitment of this asteroid on some reefs when, on other reefs, it maintains a low population density. The natural life expectancy, larval dispersal and adult migration of this asteroid, while central to an understanding of the phenomenon, are not understood sufficiently (Moore, 1978). The role of natural predators in maintaining high diversity and the possible survival strategy of rarity in the coral reef community have not been studied adequately.

Comparative data on other coral reef asteroids might contribute usefully to an understanding, or at least, enlarge our perspective of the Acanthaster planci outbreak phenomenon. With this broad aim in mind, the present study focuses on the community ecology of asteroid species at Heron Island. The population dynamics of other coral reef asteroids might show patterns of high recruitment similar to those of Acanthaster planci. The study of the abundance, longevity, population density, diet and reproduction of other coral reef asteroid species will allow comparison with Acanthaster planci as well as provide information on the mechanisms that maintain diversity within this coral reef community.


H.L.Clark (1921) found only 3 CoTS at Mer. What is the significance of this?


Can 3 starfish represent an outbreak? – It likely depends on where they were found.

Brood or Broadcast: Why not both?

Hubert Lyman Clark visited Torres Strait in 1913 with the Carnegie Institution of Washington. He found only 3 specimens of Acanthaster at Mer but examined many others from throughout the Indo-Pacific at the Museum of Comparative Zoology. This study in Torres Strait was published as H.L.Clark (1921) and was followed in 1938 and 1946 by books on the Echinoderm Fauna of Australia.

These 3 specimens at Mer were found “on the surface of the reef and not under rocks or coral slabs”. Clark suggests further that Acanthaster is often overlooked. Pratchett et al (2017) refer to Clark (1921), the Echinoderm Fauna of Torres Strait stating:

“On the GBR, it appears likely that outbreaks of A. cf. solaris were underway in 1913, given the relative ease with which Clark [230] collected CoTS in the Torres Strait.”

230. Clark, H.L. The Echinoderm Fauna of Torres Strait: Its Composition and Its Origin; Carnegie Institution Washington: Washington, DC, USA, 1921; Volume 10, pp. 1–224.

This was suggested by Pratchett et al (2017). Morgan S. Pratchett, Ciemon F. Caballes, Jennifer C. Wilmes, Samuel Matthews, Camille Mellin, Hugh P. A. Sweatman, Lauren E. Nadler, Jon Brodie, Cassandra A. Thompson, Jessica Hoey, Arthur R. Bos, Maria Byrne, Vanessa Messmer, Sofia A. V. Fortunato, Carla C. M. Chen, Alexander C. E. Buck, Russell C. Babcock and Sven Uthicke. Thirty Years of Research on Crown-of-Thorns Starfish (1986–2016): Scientific Advances and Emerging Opportunities. Diversity 2017, 9, 41.

The evidentiary value of these 3 CoTS is unclear and it surely depends on what is meant by “likely” or “relative ease”. However, it also illustrates clearly our perception of the critical importance of population aggregation in fertilization success.

However, not all species of starfish are broadcast spawners and variation in gonopore position (oral v aboral) has been described by Hart et al. (2005) in a member of the Family Asterinidae. This variation indicates cryptic species in which “nonplanktonic offspring hatch and metamorphose without a dispersing planktonic larval phase”. Larval cloning was also identified in genera Luidia and Oreaster and another two members of the family Ophidiasteridae by Knott et al. (2003).

If either of these low-dispersal reproductive strategies ever occurred in the Family Acanthasteridae it would be of enormous ecological significance as it would greatly facilitate the establishment of small pre-outbreak local populations.

Can 3 starfish represent an outbreak? – Presently unclear.

Has such gonopore or larval variation ever been identified in CoTS? – I hope not.


Does prey abundance indicate anything about predators?


Prey abundance can be indicative of predator abundance but migration and dispersal phenomena of prey, together with attraction of predators to prey may overwhelm any simple correlation.  In this study, 24 inter-tidal species of starfish were located at Heron and Wistari Reefs and there was a large range in the abundances of different starfish species. 12 species (50%) of the species were found by sampling less than 6 hectares (5%) of the total sampled area. No specimens of the giant triton (Charonia tritonis) were located during this study conducted over several years.



When most species of starfish are rare then interestingly, there appears to be a density at which they don’t appear to occur. Is this indicative of predators? Whether a relatively abundant species such as Echinaster luzonicus or a rarer species they seem to not occur at 0.3 individuals per hectare. What could this mean about predator density?

If an assemblage of starfish species is controlled by predator abundance, would the abundance distributions of these prey species reflect the underlying predator abundance. Could the minimum at 0.3 individuals / hectare indicate something related to predator density or is it just an artifact related to sample size limitations?

If sampling could have been more intensive or extensive would the number of traverses / log abundance categories in Echinaster luzonicus for example have demonstrated a different minimum than for a rarer species? If it existed, would such variation indicate a predator’s prey preference, particularly at low prey densities?


1 species of starfish (Echinaster luzonicus) occurred with an average density of greater than 10 individuals per hectare. 8 species occurred at 1 individual per hectare. 6 species occurred at each of 0.1 and 0.01 individuals per hectare and 3 species occurred at less than 0.01 individuals per hectare. It is notable that starfish of all species were uncommon at Heron and Wistari Reefs compared with studies on reefs that have carried population outbreaks of the crown-of-thorns starfish (Acanthaster planci). It is also notable that neither the crown-of-thorns starfish (Acanthaster planci) nor the giant triton (Charonia tritonis) were located on any inter-tidal traverse during this study of 120 hectares over several years.



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General Discussion

Chapter 10. General Discussion

Population density, size-frequency and reproductive data on an assemblage of shallow water, coral-reef starfish (Asteroidea) were gathered over five years at Heron Reef. Heron Reef, which is located near the southern end of the Great Barrier Reef, has not been known to carry an outbreak of the crown-of-thorns starfish (Acanthaster planci) and its coral cover is well developed. While there has been detailed study of the starfish assemblages on some reefs that have recently undergone Acanthaster planci population outbreaks (Yamaguchi, 1975 b; 1977 a), the composition of these assemblages may well be different from pre-outbreak assemblages.

Abundance, size-frequency and reproductive data were collected by means of intertidal traverses which 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). Most traverses included both reef flat and reef crest zones, and all exposed starfish within a 4 meter width were collected. A selection of large and small, dead coral slabs occurring on these traverses were overturned and cryptic specimens located beneath these slabs were collected also. In total, 72 intertidal traverses were conducted covering an area of approximately 120 hectares (1.2 square 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. Subtidal specimens of starfish were collected on the reef slope and off-reef floor by the use of SCUBA.

Of the 25 starfish species found on Heron Reef, Asteropsis carinifera, Dactylosaster cylindricus, Fromia milleporella, Linckia laevigata, Nardoa novaecaledoniae, N. pauciforis, Ophidiaster confertus, O. granifer, O. lioderma, O. robillardi, Asterina anomala, A. burtoni, Disasterina abnormalis, D. leptalacantha, Tegulaster emburyi, Mithrodia clavigera and Coscinasterias calamaria were located only in intertidal regions. Linckia guildingii, L. multifora and Echinaster luzonicus were found predominantly in intertidal regions but some specimens were located subtidally. Culcita novaeguineae, Acanthaster planci, Fromia elegans, Gomophia egyptiaca and Neoferdina cumingi were located predominantly in subtidal habitats, but are known to occur intertidally. Culcita novaeguineae seemed to mainly inhabit the deeper coral pools adjacent to the lagoon. The low occurrence of Culcita novaeguineae on the intertidal traverses is because the traverses avoided this slightly deeper-water habitat. While Culcita novaeguineae, Fromia elegans, Gomophia egyptiaca, Linckia multifora and Echinaster luzonicus were sometimes found at the base of the reef slope, they were never observed on the sea floor away from the reef. There are no published records of these species from the off-reef floor zone (see Clark and Rowe, 1971).

“Reef” echinoderm species were separated from “mainland” species on the basis of their habitat requirements by Endean (1956) who discussed the biogeographical relationships of Great Barrier Reef species. With the exception of Ophidiaster confertus and Coscinasterias calamaria, which are essentially temperate species, 23 asteroid species found at Heron Reef can be regarded as coral-reef species and their distribution differs from species such as Astropecten polyacanthus, Iconaster longimanus, Pentaceraster regulus, Leiaster leachi, Nardoa rosea, Ophidiaster armatus, Tamaria megaloplax and Echinaster stereosomus. These latter species appear to be predominantly off-reef, sea-floor species that are widely distributed throughout the shallow waters of tropical and sub-tropical Queensland. The predominantly reefal distribution of the long-spined, corallivorous species, Acanthaster planci, contrasts with that of its generally deeper water, short-spined, molluscivorous relative, A. brevispinus. Only small fissiparous specimens of Coscinasterias calamaria were located on Heron Reef. Large adults of this and other forcipulatid species are predators in temperate communities. Both Ophidiaster confertus and Coscinasterias calamaria appear to be predominantly temperate species that occur in Australian mainland waters but which have extended their ranges to reefs at the southern end of the Great Barrier Reef.

The finding of 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 represent new records for Heron Reef. In some cases these represent new records for the Great Barrier Reef, and in other cases known ranges on the Great Barrier Reef have been considerably extended. This study has also provided the first record of the predominantly temperate species, Coscinasterias calamaria on the Great Barrier Reef.

The distinguishing characteristic of coral-reef species of starfish is their possession of a spatial distribution that never extends into the deeper parts of the off-reef floor zone. Such a spatial distribution would preclude between-reef migration by post-larval stages of these species. It is not known why some species of starfish are essentially restricted to coral reefs, but it is likely that such species would differ in their physiological and / or ecological requirements from species that occur elsewhere. While the intertidal region of a coral reef undergoes both temperature and salinity fluctuations (Maxwell, 1968), a substrate of coral sand and rubble (aragonite not calcite) would ensure complete carbonate saturation of the waters and hence the waters would be well buffered against pH changes. Some species of starfish that occur exclusively in association with coral reefs may have narrow pH tolerances. Other species may have evolved interdependencies that involve settlement or survival conditions that are only present within the coral reef ecosystem. Likewise, with respect to the coral reef ecosystem itself, it might be expected that species that occur predominantly in one of the major zones of a coral reef (e.g. the reef flat) would differ in their physiological and / or ecological requirements from species that occur in several of these zones. For example, they might differ in their degree of tolerance to sub-aerial exposure at low tide or in their biotic associations.

Patches of localised high density were observed within the populations of some of the smaller-bodied species of coral-reef starfish that were studied. However, each of these patches appeared to be restricted to a very small area. For example, the small-bodied starfish Disasterina abnormalis occurred at an average density of over eight individuals per square metre at one location on the northern reef crest but 100 metres away (still on the reef crest) its density was less than one individual per square metre. This region of high density of Disasterina abnormalis appeared to be confined to a narrow strip behind a rubble bank and this species was not found on 25 of the 72 traverses that were made. In this region, Disasterina abnormalis was highly clumped (at the metre square scale) in one sampling period and randomly distributed in another sampling period.

Echinaster luzonicus was the most abundant starfish found on the intertidal traverses and Linckia multifora was the next in order of decreasing abundance. Both of these small-bodied species were found in relatively high numbers in some regions of the reef crest. The large-bodied starfish Linckia laevigata was third in order of decreasing abundance on the traverses but its maximum density did not approach that of either of the preceding species anywhere at Heron Reef. The density of Linckia laevigata at Heron Reef appeared to be low compared with its density on reefs that are known to have carried an outbreak of Acanthaster planci (Laxton, 1974; Yamaguchi, 1977 a; Thompson and Thompson, 1982; Klumpp and Pulfrich, 1989). Laxton (1974) suggested that Linckia laevigata may either increase its numbers or extend its range following outbreaks of Acanthaster planci. Disasterina abnormalis was fourth in order of decreasing abundance and occurred at the highest local density of any species of starfish during this study.

The intertidal traverses made during this study covered an area of 125 hectares. Over 1400 individuals of Echinaster luzonicus were located and over 100 individuals of each of another 8 species were located. However, fewer than 25 individuals of each of the remaining 15 species were located. The low starfish density found at most locations on Heron Reef contrasts markedly with the high densities recorded for asteroids of temperate communities (Loosanoff, 1961; 1964; Mauzey et al, 1968; Menge, 1975; Dayton et al, 1977; Birkeland et al, 1982; Stevenson, 1992).

Traverse sampling resulted in the location of a total of 24 species of intertidal starfish. For 10 of these species, a sufficient number of individuals was obtained for reproductive analysis and for 7 of these species size-frequency variation was examined over different sampling periods. Traverse sampling enabled data to be gathered on a large spatial scale (125 hectares) which facilitated both the collection of sufficient specimens for reproductive and size-frequency analysis as well as the determination of large scale non-randomness in the spatial distribution of these species.

While the intertidal traverse data did not allow small-scale analysis of either spatial or temporal abundance variation, the starfish assemblage at Heron Reef clearly embraces a highly diverse and spatially heterogeneous group of species. Individuals of each species were extremely non-random (clumped) in their spatial distribution. Only Echinaster luzonicus was sufficiently abundant and widespread to be found on all but three of the traverses. Linckia laevigata and Nardoa novaecaledoniae were not located on 10, Nardoa pauciforis was not located on 19, Linckia multifora was not located on 22, Disasterina abnormalis was not located on 25, Asterina burtoni was not located on 26 and Linckia guildingii was not located on 34 of the 72 traverses made. Representatives of the remaining species were not found on the majority of these intertidal traverses.

With the exception of Echinaster luzonicus, the abundance distributions of all of the species had a modal traverse density of zero individuals per hectare. This indicated that, with the exception of Echinaster luzonicus, each coral-reef starfish species was not represented on a large number of the traverses. The more common of these species possessed a bimodal abundance distribution which indicated that they were non-random (patchy) in their spatial distribution. For these species, there were many traverses where both zero and a relatively large number of individuals per hectare were recorded and very few traverses where intermediate (mean) densities occurred.

Table 4.1 lists the mean density per hectare and the variation that occurred in the mean density of each species between traverses. In all species the standard deviation was greater than the mean density. These data together with the bimodal population distribution data (Figures 4.2 to 4.12) indicate that large scale aggregation occurs in all of the species with the possible exception of Echinaster luzonicus. A stratified-random sampling procedure, using multiple belt transects would have allowed a detailed comparison of starfish abundances between different habitats. However, when used on a reef that has low general starfish abundance, such a sampling method would not have located a sufficient number of individuals in the limited time available for field studies at Heron Reef to permit a statistically valid size-frequency and reproductive analysis.

A mode in the abundance distribution was recorded at between three and 10 individuals / hectare in six species (rank 1 – 6) and at between one and three individuals / hectare in another six species (rank 7 – 12). The remaining twelve species (rank 13 – 20) were encountered so infrequently that the only mode in the abundance distribution of each species was at zero individuals per hectare. Five species were sufficiently uncommon (rank 20) to be encountered on only one intertidal traverse during the entire study.

Culcita novaeguineae, Fromia elegans, Gomophia egyptiaca and Nardoa rosea were encountered much more frequently in sub-tidal traverses than they were on intertidal traverses. Disasterina leptalacantha was recorded more frequently at Heron Island by Endean (1957) than it was in this study, but there may have been confusion between the two similar congeneric species in the earlier study. Similarly the ecological distinction between Asterina anomala and Asterina burtoni is unclear. The observed variation in the abundance of Asterina burtoni at Heron Reef is consistent with the results of Achituv and Sher (1991), but the mode of reproduction appears to be different.

The very small and highly cryptic species Disasterina abnormalis occurred periodically with high abundance at one location on the inner reef crest. It was possible to sample this species in this localised habitat by means of metre square quadrat sampling (Table 4.2). The data obtained do not represent the abundance of this species generally, but serve to illustrate clearly the enormous spatial and temporal variation that occurs in the population distributions of this opportunistic species.

Although the diets of the coral-reef starfish species encountered were not studied in detail, many of them appeared to feed on epibenthic felt. In every coral reef zone, some species sought no refuge and occurred in exposed situations. Clear examples of niche (dietary or microhabitat) specialisation are known only for Culcita novaeguineae and the predominantly subtidal species Acanthaster planci both of which feed primarily on corals. Competitive interactions were not studied, but many species occurred at a sufficiently low density that they may not be resource limited.

Because of the patchy nature of the spatial distributions of all of the coral-reef asteroid species, size-frequency analysis over multiple sampling periods (Tables 5.1 to 5.12 and Figures 5.1a to 5.10d) was considered the most appropriate means of establishing the existence of population stability. Obvious changes in abundance due to either sexual or asexual recruitment, and significant changes in mean individual size were observed in the populations of Linckia multifora, Disasterina abnormalis and Echinaster luzonicus (Table 8.1 and Figures 8.1a to 8.3c). While some recruitment and some change in abundance was noticed in both Ophidiaster granifer (parthenogenetic) and Asterina burtoni (hermaphroditic), no significant change occurred in the mean individual size of either species. Linckia guildingii, Linckia laevigata, Nardoa novaecaledoniae and Nardoa pauciforis exhibited only small changes in mean individual size and these species did not fluctuate greatly in abundance during the period of study. Also, the population structure of these species appeared to be adult dominated and juveniles were encountered only rarely.

The remaining species were not found in sufficient numbers for meaningful statistical analysis of size-frequency data. Their populations were sparse and juveniles were not encountered except for one specimen each of Culcita novaeguineae, Fromia elegans and Gomophia egyptiaca. Their populations appeared to be adult dominated. Juveniles of Culcita novaeguineae and Fromia elegans were not encountered subtidally despite the existence of a subtidal population of adults. One juvenile of Acanthaster planci was located at the base of the reef slope.

Culcita novaeguineae and many other coral-reef starfish species were not encountered in sufficient numbers to warrant an examination of their population stability. The study of Laxton (1974) appeared to show a greater abundance of Linckia laevigata on the reef flat at Heron Reef than was observed in this study. Laxton suggested that this species may vary its distribution range following outbreaks of Acanthaster planci. It is possible that large-bodied species of starfish, such as Linckia laevigata, undergo large scale aggregation behaviour but the limited duration of this study precluded examination of such long period fluctuations.

Grassle (1973), Sale and Dybdahl (1975), Talbot et al. (1978) and Hutchings (1981) all found that most coral-reef species are rare. Endean and Cameron (1990 a) mention that the high incidence of rare species in the coral-reef community contributes markedly to species diversity. Some of the rarer species of coral-reef starfish are known from only a few specimens and their low-density populations defy our normal understanding of population dynamics and reproductive strategies. It is not clear how these species survive or whether their populations are predator, resource or recruitment limited. Species such as Tosia queenslandensis, Ophidiaster lioderma and Tegulaster emburyi have always been considered rare throughout their geographical range. Although nothing is known of their reproductive cycles, if they are truly rare and valid “biological” species, then they might be expected to exhibit mechanisms such as population aggregation, asexual reproduction, parthenogenesis or hermaphroditism that would facilitate their persistence at low population densities.

Inter-coelomic injection with the hormone 1-methyl adenine was used to determine the sex ratio, reproductive maturity and type of larval development of several of the species. It can be seen from Tables 6.1 to 6.8 and Figures 6.1 to 6.8 that eight of the more common species appeared to demonstrate an annual sexual reproductive cycle. Disasterina abnormalis possessed small (non-yolky) sticky eggs that adhered to the substrate immediately following their release from the gonopores. Small juveniles of Disasterina abnormalis were relatively common in one highly localised area at Heron Reef, but high settlement was not observed in any of the other species. The remaining seven species possessed eggs that dispersed and underwent either planktotrophic or lecithotrophic larval development. No species were observed to brood larvae.

Culcita novaeguineae, Acanthaster planci, Linckia guildingii and Linckia laevigata were observed releasing eggs that contained little yolk and underwent planktotrophic development. Fromia elegans, Gomophia egyptiaca, Nardoa novaecaledoniae, Nardoa pauciforis, Ophidiaster granifer and Echinaster luzonicus were observed releasing eggs that contained large amounts of yolk and underwent lecithotrophic development. Specimens of both Linckia multifora and Asterina burtoni were injected regularly, but did not release gametes during the entire study.

Vance (1973) and Yamaguchi (1973 a, 1973 b, 1977 b) suggested that lecithotrophic development is an adaptation to high predation or starvation of larva because with this development the length of larval life can be shorter than with planktotrophic development. On Heron Reef, and possibly the Great Barrier Reef in general, where many reefs exist in relatively close proximity, lecithotrophic genera such as Nardoa, Fromia and Echinaster might be expected to be better represented than they are on widely scattered atolls. At Heron Reef, the larger-bodied species namely, Culcita novaeguineae, Acanthaster planci, Linckia guildingii and Linckia laevigata all liberated dispersing, small eggs that underwent planktotrophic development while the smaller-bodied species, together with Nardoa novaecaledoniae and Nardoa pauciforis (both intermediate in body size), all liberated larger eggs that underwent lecithotrophic development. The small, sticky eggs of Disasterina abnormalis resulted in high localised settlement and this strategy appeared to be unique amongst the starfish species that were studied at Heron Reef.

In addition to the species that demonstrated a sexual reproductive cycle, Linckia guildingii, Linckia multifora, Ophidiaster robillardi and Echinaster luzonicus reproduced asexually and exhibited comet stages while Asterina anomala and Coscinasterias calamaria reproduced asexually by binary fission. All small specimens of these species exhibited the characteristics of either autotomous propagation (see Rideout, 1978) or binary fission. While all of the arms might look quite similar in some small individuals of autotomous species, the original arm from which the others regenerated was always apparent following closer examination. All specimens of fissiparous species showed signs of recent binary fission.

While specimens of both Linckia guildingii and Echinaster luzonicus were observed releasing gametes in response to injection with 1-methyl adenine, no sexually-propagated juveniles were observed in the populations of any species that reproduced asexually. With the exception of Linckia guildingii, large bodied species of coral-reef starfish do not appear to have a small scale (low dispersion) reproductive strategy. This could indicate that survival of offspring is more likely away from adult populations. The advantages of a high dispersion reproductive strategy must be balanced against the high dispersive loss resulting from the relative isolation of reefs of the Great Barrier Reef and elsewhere.

Linckia multifora and Echinaster luzonicus were the only asexually reproducing species in which high rates of autotomy were observed and the location of comet stages and adults in various stages of regeneration is evidence of relatively high asexual recruitment. These three species had the highest localised abundances of any of the coral-reef starfish but also had highly patchy spatial distributions. The remaining species never occurred at densities comparable with these species even though the average density of Linckia laevigata was higher than the average density of Disasterina abnormalis. While comet stages and adults in various stages of regeneration were observed in Linckia guildingii, this species did not show evidence of high asexual recruitment.

With the exception of Disasterina abnormalis (see Chapter 6), all the species of starfish at Heron Reef either possessed a planktonic dispersive larval phase or were not observed to reproduce sexually . The largest-bodied persistent species released planktotrophic eggs while the opportunist species were either lecithotrophic, hermaphroditic (Asterina burtoni), parthenogenetic (Ophidiaster granifer) or solely asexually reproducing (Linckia multifora). Nardoa novaecaledoniae, Nardoa pauciforis and Gomophia egyptiaca would appear to be of intermediate position and the taxonomic position of Asterina anomala is unclear.

All of the large-bodied species studied liberated either eggs or sperm directly into the water column and fertilisation was external. While possible pairing was observed in crowded aquaria (following injection with 1-methyl adenine), no species were observed mating in the field as has been recorded by Run, Chen, Chang and Chia (1988) for the tropical species Archaster typicus. Slattery and Bosch (1993) also recorded mating behaviour in an Antarctic species of starfish.

Ormond et al. (1973) discussed the consequences of spawning aggregations of Acanthaster and suggested that the increased proximity of adult starfish may enhance the chances of fertilisation, especially if synchronous spawning takes place. It was suggested by Lucas (1984) that a conspecific stimulus would induce synchronous spawning in Acanthaster planci and a delayed spawning activity in dispersed individuals of Acanthaster planci was observed by Okaji (1991). It was suggested that this delay reflected less frequent stimulus from conspecifics in dispersed populations compared with aggregated populations and that synchronous spawning induced by such stimulus would lead to higher rates of fertilisation when the animals formed an aggregation. Evidence of the existence of sexual pheromones in starfish was presented by Miller (1989).

The effect of sperm dilution, adult aggregation and synchronous spawning upon the fertilisation of sea-urchin eggs was reported by Pennington (1985). Pennington concluded that significant fertilisation occurred only when spawning individuals are closer than a few metres. The consequences of water mixing and sperm dilution for species that undergo external fertilisation were discussed by Denny and Shibata (1989) who found that only a small fraction of ova were fertilised other than in densely packed arrays. They commented that the low effectiveness of external fertilisation may change the way one views the planktonic portion of such life cycles and suggested that this could serve as a potent selective factor. For the rarer sexually reproducing species, it is apparent that aggregation resulting in the occurrence of an opposite sexed conspecific within the effective fertilisation distance is a condition precedent to successful reproduction. The degree of reproductive success may be strongly dependent on just how close the rare spawning individuals are to each other. While the results of Babcock and Mundy (1992) appear inconsistent with these previous studies, the population density and degree of adult aggregation would be highly relevant factors for both the synchrony of spawning and the level of egg fertilisation in externally fertilising dioecious species. If a low density starfish population is highly dispersed then the degree of egg fertilisation would be much lower than if aggregation occurred.

The above factors influence recruitment as do many other factors such as dispersion loss (Atkinson et al, 1982; Dight et al., 1990 a, b; Black and Moran, 1991; Wolanski, 1993) and starvation of larvae (Birkeland, 1982; Olsen, 1987). These factors, together with the mortality of juveniles prior to first reproduction (Endean, 1977; 1982; McCallum et al, 1989), might result in this assemblage being recruitment limited as suggested for certain species of coral-reef fish by Doherty (1982). If the process of recruitment is completed when an organism enters the breeding population, then a species could be regarded as recruitment limited if mortality of its larvae or juveniles was sufficiently great to maintain adult populations at a low density. This may occur as a result of either low egg fertilisation or high mortality of larvae or juveniles.

On reefs such as Heron Reef that have low adult starfish abundance, predation of adult starfish appears to be a rare event and was not studied because of logistic constraints. While the giant triton (Charonia tritonis) is a voracious predator of large juvenile and adult starfish (Endean, 1969; Pearson and Endean, 1969), no specimens of this species were observed at Heron Reef either subtidally or on intertidal traverses during the entire study. The giant triton is cryptic and it is extremely difficult to survey the population density of this predator. It is likely that there are other predators of coral-reef starfish, particularly fishes. Other predators (see Endean and Cameron, 1990 b) have been found for Acanthaster planci. If starfish populations are stable then mortality (including lethal predation) will match recruitment which appeared to be extremely low in the populations of large bodied coral-reef starfish. If starfish populations are maintained at a low adult density, then predation on pre-adults could be a major factor in controlling the assemblage.

An increase in anti-predatory structures with decreasing latitude was found by Vermeij (1978) and Blake (1983) suggested the existence of a similar pattern in sea stars. Pearson and Endean (1969) and McCallum et al. (1989) reported a high incidence of sub-lethal predation in populations of Acanthaster planci. Blake (1983) commented that the asteroid fauna of the Indo-West Pacific are dominated by the order Valvatida and members of this order have the best developed anti-predatory devices. Yamaguchi (1975 b) commented on the difference between adult and juvenile asteroid habits and suggested that the heavy armour of exposed adult asteroids might reflect heavy predation pressure.

In addition to the protection afforded by structural features, many species of starfish are protected from generalist predation by the possession of skin toxins (Riccio et al., 1982, 1985; Gorshkov et al., 1982; Minale et al., 1984; Narita et al., 1984; Noguchi et al., 1985 a,b; Miyazawa et al., 1985; 1987; Kicha et al., 1985; Shiomi et al., 1988; Shiomi et al., 1990; Zagalsky et al., 1989; Iorizzi et al., 1991; Bruno et al., 1993; Casapullo et al., 1993). These skin toxins have been shown to be toxic to some fish species (Rideout, 1975). The role of echinoderm toxins as a defence against predation has been discussed extensively (Bakus, 1974; Green, 1977). Cameron and Endean (1982) discussed the role of venomous devices and toxins as defences against predation and Endean and Cameron (1990 a) have noted that persisters are often toxic. There is little information available on the toxicity of juvenile starfish to potential predators. Eggs and juveniles of Acanthaster planci are known to carry toxins. It has been proposed that the production of toxins for defence incurs an energy cost which is balanced against the probability of mortality (Eckardt, 1974) but in some species, toxins might be metabolic by-products that incur no energy cost in their synthesis.

In some groups of starfish behavioural mechanisms are used as defences against predation and Blake (1983) suggested that both Luidia and Astropecten have broad open ambulacral furrows because they were predators on active solitary forms where increased skeletal mobility was essential. Because both these active, hunting genera live on and within unconsolidated sediment they avoid predation by burrowing which is facilitated by the paxillose nature of their aboral surface.

Another behavioural defence possessed by asteroids is the autotomy of arms. Of the coral-reef starfish studied, Linckia guildingii, Linckia multifora, Ophidiaster robillardi and Echinaster luzonicus are capable of regenerating a complete individual from the distal section of one arm. These autotomous species were extremely aggregated in their spatial distribution, suggesting that population growth occurs with little dispersal of individuals.

In species of starfish that do not reproduce by autotomy, specimens are often observed in various stages of regeneration following loss of one or more arms. McCallum et al (1989) reported that 40% of the adult individuals in a population of Acanthaster planci showed signs of arm regeneration. Cameron and Endean (1982) suggested that autotomy is an adaptation to predation and Birkeland et al (1982) observed autotomy in their study of asteroid predatory interactions. At Heron Reef, many individuals were observed in various stages of regeneration following autotomy of one or more limbs. A number of tropical asteroids are known to undergo regular autotomy (Rideout, 1978; Yamaguchi, 1975 b) and Blake (1983) commented that interpretation of the skeleton can be difficult as it has more than one function and protection against predation can be accomplished by many mechanisms (e.g. Bullock, 1953; Feder, 1963; Mauzey et al., 1968; Ansell, 1969; Birkeland, 1974; Phillips, 1976; Dayton et al., 1977; Jost, 1979; Schmitt, 1982; Stevenson, 1992; Iwasaki, 1993).

In the species that reproduce by autotomy, it is not known to what extent the autotomisation of a limb is caused by physical disturbance such as predation. While direct predation was not observed, large individuals of the large-bodied species of starfish often had their arms intertwined with the substrate such that they were difficult to dislodge. In the large-bodied species that only reproduce sexually, parts of a limb and even one or two whole limbs were observed to be missing from some individuals. The existence of such behaviour together with the observations of missing arms in species that do not reproduce asexually, indicates that sub-lethal predation does occur. Whether it is significant in the regulation of the Heron Reef asteroid assemblage will depend on the age structures of the populations. Sub-lethal predation of adults will be especially important if a species is long lived.

This study has examined the population dynamics of both relatively common and relatively rare species of coral-reef starfish. Although some species were not sufficiently numerous to provide statistically satisfactory numbers of records, data were gathered on their habitat, size, spatial pattern and relative abundance. It is clear that the majority of species of intertidal starfish at Heron Reef were sufficiently uncommon to preclude small scale methods of population examination. There is considerable disagreement over the accuracy of large scale methods (manta tow) to examine subtidal populations of starfish (Fernandes, 1990; Fernandes et al., 1990; Moran and De’ath, 1992 a,b). However, the determination of large scale, non-random variation in the distribution of any species is a condition precedent to the determination of its overall abundance. In the estimation of average density, methods of both sampling and analysis must adequately consider the high standard error of the mean. All conclusions must have due regard to the bimodality and skewness of the abundance distributions of starfish.

Some species, namely Disasterina abnormalis, Asterina burtoni, Ophidiaster granifer, Linckia multifora and Echinaster luzonicus, could be regarded as opportunist species as they were characterised by possessing relatively abundant populations with relatively large fluctuations in mean individual size. These invariably small-bodied species demonstrated all of the typical opportunist characteristics which are short life, high recruitment and high mortality (see Endean and Cameron, 1990 a).

Other species, namely Culcita novaeguineae, Linckia laevigata, Linckia guildingii, Nardoa novaecaledoniae and Nardoa pauciforis could be regarded as persistent species and were characterised by less abundant populations with relatively smaller fluctuations in mean individual size. These invariably medium to large bodied species demonstrated all of the typical persister characteristics which are long life, low recruitment and low mortality. A large proportion of coral-reef starfish were sufficiently uncommon to preclude any analysis of either their abundance or size distributions. Apart from the knowledge that they remained rare through the study period of 5 years, little is known of their natural history. Because of their extreme rarity, which is a characteristic of persisters, they might be placed in this category pending further investigation. Of the 25 intertidal species of starfish, five species (20 percent) were characteristic opportunist coral-reef species and 18 species (72 percent) were characteristic persister coral-reef species (stable abundance and size distribution or remained uncommon throughout study). Only two species (8 percent), namely Ophidiaster confertus and Coscinasterias calamaria were sub-tropical, rocky-reef (mainland) species that had extended their ranges to embrace the southernmost reefs of the Great Barrier Reef.

The longevity of a species is determined by the relative probability of juvenile and adult survivorship. In the simplest case, if the probability of a sexually mature organism’s survival from one reproductive season to the next is greater than the probability of one of the offspring reaching sexual maturity, then the species will exhibit iteroparity (see Cole, 1954; Murphy, 1968; Goodman, 1974; Stearns, 1977; Roff, 1981; Ebert, 1982). Although neither predation nor mortality was observed during this study, both low adult mortality and relative longevity can be inferred from the stability of the size-frequency distributions of the persistent species studied. This contrasts with the large population fluctuations and instability of the population structure of the opportunist species studied.

Most marine benthic invertebrates have a high energy cost associated with reproduction (Mileikovsky, 1971). Under differing selection pressures, it has been suggested that long life can be associated with either variable recruitment (Sterns, 1977) or fixed low recruitment (Charnov and Schaffer, 1973; Schaffer, 1974; Ebert, 1982). McCallum (1987) and McCallum et al. (1989) have suggested that Acanthaster planci is recruitment limited by juvenile and sub-adult predation.

A model relating to our perception of the life history of all organisms, referred to as r- versus K- strategy, was reviewed by Stearns (1977). The different survival characteristics in the model were thought to have evolved in response to specific types of environments (Murphy, 1968; Hairston, Tinkle and Wilbur, 1970). The spectrum of existing life history attributes, apparent in any community study (see e.g. Menge, 1975; Vance, 1973), was considered to represent many points on a continuum between the conceptually ideal r- strategists and K- strategists.

It has been suggested that the dispersal stage of a population spreads the risk of local extinction in space and time (Den Boer, 1971; Scheltema, 1971; Strathmann, 1974). Opportunists survive by being able to colonise regions quickly following disturbance. In this regard, an important distinction must be made between equilibrium and non-equilibrium populations in terms of adaptive characteristics (Caswell, 1982; Ebert, 1985). High spatial and temporal variation in population size seems to characterise the typical opportunists.

The degree of spatial and temporal stability in the population of a species determines its position on a theoretical opportunist – persister continuum. Each species was viewed in this context and a basic dichotomy was observed. Because it does not require presumptions of carrying capacity, and inferences about competition, the opportunist / persister model of Endean and Cameron (1990 a) seems to best describe this low density assemblage of coral-reef starfish. Stable ecosystems should be characterised by small fluctuations of their component species. However it is clear that the apparent stability or instability of any biological system is dependent not only on the spatial and temporal scales of observation (Bradbury and Reichelt, 1982; Sale, 1984; Weiss, 1969) but also on the particular subset of species that is examined.

The observed level of numerical and size-frequency stability in the persistent coral-reef asteroid species is consistent with a model of community equilibrium. It is clear that mortality, dispersion, larval survival and settlement phenomena did not result in widely varying size structures or greatly differing adult numbers from one year to the next over a period of 5 years. The vast majority of species of coral-reef starfish in the assemblage studied were characterised by continuing low abundance. It would appear that when a rare, large-bodied starfish is established in its adult population, it is likely to be long lived. Acanthaster planci is a member of this coral-reef starfish assemblage and Cameron (1977) has suggested that only when the coral reef ecosystem is drastically altered can such a rare and long-lived carnivore undergo population outbreaks. This restriction may also apply to other persistent species in the coral-reef starfish assemblage.

Factors such as high gamete dilution (Rothschild and Swann, 1951; Pennington, 1985; Denny and Shibata, 1989; Epel, 1991), as well as basically unpredictable environmental factors such as larval mortality and enormous potential larval dispersion can affect the number of larvae reaching a reef. Because the area of coral reef in the Great Barrier Reef region is relatively small compared with the area of sea surface in the region, the probability of a planktonic starfish larva reaching a coral reef is quite low. Also, if predation on post-settlement juveniles is intense then recruitment will be low. In low density starfish populations, the aggregation of adults prior to spawning may be essential to the reproductive success of a rare species. Because successful recruitment implies that post-settlement juveniles must survive to enter the breeding population, predation on juveniles as well as sub-lethal predation of adults (when loss of gonad affects fecundity) are both forms of recruitment limitation.

The results presented in this study are in accord with the hypothesis of Endean and Cameron (1990 a) that complex, high diversity assemblages of coral-reef animals are characterised by a predominance of rare, long-lived species with relatively constant population sizes and size structures and a minority of relatively common, short-lived opportunistic species characterised by fluctuating population sizes and size structures.


Relative Abundance and Diversity


Chapter 9. Relative Abundance and Diversity

9.1 Introduction

In addition to the high diversity of the coral reef ecosystem, a feature of this ecosystem is the large number of rare species within each taxonomic group. The general relation between the number of species and the number of individuals in a sample of a population was discussed by Fisher, Corbet and Williams (1943), who commented that species are not equally abundant, even under conditions of considerable uniformity. They went on to state that the majority of species are comparatively rare while only a few are common.

It is not known whether the rarity of a species is indicative of its low competitive ability or alternately whether the species is restricted to specialised microhabitats with excess recruitment eliminated by predators (Hairston, 1959; Kunin and Gaston, 1993). The relative abundances of the species in a diverse assemblage are often distributed over many orders of magnitude. As a result, qualitative representations of abundance such as common, moderately abundant or rare must be arbitrary in their assignment.

Many different mathematical models have been proposed to describe satisfactorily the relationship that exists between the relative abundances of different species in an assemblage. While each model has been criticised extensively (Hurlbert, 1971; Abbott, 1983; Connor and McCoy, 1979; Connor, McCoy and Cosby, 1983; Martin, 1981; McGuiness, 1984; Pielou, 1981; Sughihara, 1981), each attempts to quantify the degree of variation in the relative abundances of the different species. The most noticeable result of this abundance variation is the different rates at which species accumulate with increased sampling in different assemblages.

9.2 Methods

The population density of each species and the relation between sample area and the number of individuals in the sample was calculated in Chapter 4. The relation between sample area and the total number of species in the sample (the species : area curve) was also calculated from the traverse data. The cumulative number of species was compared with the cumulative area of the traverses (starting at the completion of Traverse 1 and continuing through to the completion of Traverse 72). This comparison was also undertaken with the natural logarithm of the cumulative area of the traverses.

Shannon’s Evenness Index (see Pielou, 1981) which is the expression (S P(log P)) / log S, where P is the proportion of each species in the community, and S is the total number of different species, is often used to display the relative richness of various communities. Shannon’s Evenness was calculated for each traverse individually and cumulatively starting with Traverse 1 and ending with Traverse 72.

The relation between the numerical abundance of each species and the rank abundance of each species was calculated by ordering the numerical abundance from most common (rank 1) to least common (equal rank 20 for five species). Percent relative abundance was the ratio of the numerical abundance of each species to the total asteroid abundance.

9.3 Results

Table 9.1 lists the numerical, relative and rank abundances of each species located on the intertidal traverses. Figure 9.1a graphs the relation between the numerical abundance of a species and its rank abundance. Figure 9.1b graphs the relation between (log) relative abundance and rank abundance. Figures 9.2a,b graph the species : area and species : (log) area relation. Figures 9.3a,b graph the relation between Shannon’s Evenness and cumulative area and cumulative (log) area. Natural logarithms were used in all these calculations. Shannon’s Evenness as a measure of diversity has the advantage that the index is a ratio of attained diversity over maximum possible diversity and is therefore independent of the base of logarithm which has been chosen.

Table 9.1

The numerical abundance, relative abundance and abundance rank of inter-tidal asteroids at Heron Reef.

SPECIES                 NUMERICAL     RELATIVE      RANK 
Culcita novaeguineae          15          **          13    
Asteropsis carinifera          3          *           19
Dactylosaster cylindricus      1          *           20
Fromia elegans                16          **          12
Fromia milleporella            1          *           20 
Gomophia egyptiaca             6          *           16 
Linckia guildingii           116          ***          8
Linckia laevigata            509          ***          3
Linckia multifora            522          ***          2
Nardoa novaecaledoniae       326          ***          5
Nardoa pauciforis            187          ***          7
Nardoa rosea                   1          *           20
Ophidiaster armatus            4          *           17
Ophidiaster confertus          4          *           17
Ophidiaster granifer         116          ***          9
Ophidiaster lioderma           1          *           20
Ophidiaster robillardi        24          **          10
Asterina anomala              17          **          11
Asterina burtoni             208          ***          6
Disasterina abnormalis       500          ***          4
Disasterina leptalacantha      7          *           14
Tegulaster emburyi             1          *           20     
Echinaster luzonicus        1402          ****         1 
Coscinasterias calamaria       7          *           14
*        Very rare <10 :** rare 11-100 :*** common 101-1000 :**** abundant>1000    

9.4 Discussion

The generally low abundances of most of the species of starfish at Heron Reef precluded the use of quadrats in general sampling. Because the traverse method will miss many cryptic individuals and provide only an approximate area measurement, the species diversity and species accumulation figures are only approximate. It would appear from Table 4.1 that most species occurred at a density that was less than one individual per hectare, with many species being far less abundant. It should be noted that traverse sampling will underestimate the density of all cryptic species, and will also fail to detect species that are both rare and cryptic.

McGuiness (1984) suggested that the use of species : (log) area or (log) species : (log) area for the display of the species : area relationship should be based on the underlying relative abundances of the species. The slope of the species : (log) area relationship, the slope of the (log) relative abundance : rank abundance relationship and Shannon’s Evenness index are all indices of diversity. These allow a direct comparison to be made between different assemblages. Not only do these indices consider the number of species, they also express the inherent range of abundance between most common and least common within the assemblage (Connor and McCoy, 1979; Connor and Simberloff, 1979; Connor et al., 1983).

Figures 9.1a,b show that the four most common species account for 70% of the total number of individuals in this assemblage. However, even Echinaster luzonicus, the most abundant species, had an average density of only 16 specimens per hectare. Of the 24 species of asteroid that occurred in the traverse samples, five species occurred only once. Presumably the species which were not found during this study, but which are known from the locality, occur with even less frequency than these five. Less than ten specimens of each of another six species were located on the intertidal traverses. Hence, 11 of the 24 species are regarded as very rare. Less than 25 specimens of another three species were found and these are regarded as rare. Thus a majority of the asteroid species found at Heron Reef are rare or very rare.

The slope of the regression line in Figure 9.1b is a measure of the diversity of this asteroid assemblage. The steeper the line the greater the range of relative abundance within a certain group of species. The less equal the relative abundances, the lower the diversity as measured by most diversity indices. Community studies often show a log-normal relationship in relative abundance, in which most species occur with close to the average abundance (Pielou, 1981). This assemblage of coral-reef asteroids does not clearly demonstrate this relationship, but this result may be attributable to an inadequate number of both species and individuals in the present study. The order of the species in Figures 9.1a,b is that of numerical abundance. If biomass or some other parameter was chosen as a measure of abundance, then the order of the species may change but the slope of the regression line might not alter greatly.

Figures 9.2a,b illustrate the species : area curve for the Heron Reef asteroid assemblage. The slope of the (log) area regression line is independent of the units used to measure area. Whether they be square metres or hectares, providing the habitat continues, the species will accumulate at a rate determined only by the relative abundances of the species in the assemblage. If there is some finite species pool which obviously cannot be exceeded, then the curve will become asymptotic.

The pronounced dips in Figures 9.3a,b are a result of small scale patchiness in the distribution of Echinaster luzonicus and Disasterina abnormalis. After continued sampling, the effect of this high localised abundance was rendered insignificant in the total diversity.

Figures 9.1a to 9.3b all relate to the one ecological parameter, namely the relative abundances of the species within this assemblage. This will determine the rate at which the species accumulate in a species : area curve, as well as the diversity as measured by most diversity indices.

The richness of the coral-reef asteroid assemblage at Heron Reef is unable to be compared directly with that of other coral-reef asteroid assemblages either on the Great Barrier Reef or elsewhere. This is because the extent of sampling has not been quantified in the majority of biogeographical studies. Because the area sampled determines the number of species in a sample of any assemblage (Fisher, Corbet and Williams (1943), the large number of species found at Heron Reef may be a result of the intensive sampling. Even so, it would appear from the linearity of Figures 9.2b that additional species of starfish occur intertidally at Heron Reef, but these species are either extremely rare or cryptic.

It is apparent that Heron Reef carries a rich and diverse asteroid fauna, 24 species belonging to six families having been found intertidally in 120 hectares during this study. The linearity of the species : (log) area relationship for the intertidal asteroid assemblage at Heron Reef indicates that additional species are still to be found. Indeed, Mithrodia clavigera was located subsequent to the traverses and Endean (1956) found three species (Acanthaster planci, Ophidiaster watsoni and Anseropoda rosacea) in the area of the traverses that were not found during the current study.