Zooplankton abundance and grazing at Davies Reef,Great Barrier Reef,Australia

Zooplankton abundance and grazing on autotrophic and heterotrophic particulate matter were measured along a transect across Davis Reef (18°5S; 147°39E) and in the back-reef lagoon over tidal and diel cycles during austral winter (August 1984). Zooplankton entering the reef from the surrounding shelf waters decreased in abundance over the reef flat, presumably because of predation. Within the reef lagoon, maximum daytime densities of pelagic copepods occurred during high water, suggesting an external input. At night, water-column zooplankton biomass increased by a factor of 2 to 3 due to the emergence of demersal reef zooplankton. Zooplankton grazing rates on heterotrophic particulate matter (bacteria + detritus and Protozoa) compared to phytoplankton were higher on the reef flat than on the fore-reef or lagoon. Within the lagoon, zooplankton grazing rates on heterotrophic material were maximum during high water, coincident with maximum tidal concentrations of particulate organic carbon. The combined demersal and pelagic zooplankton community were often able to crop 30% of the daily primary production by >2µm phytoplankton. However, >50% of phytoplankton biomass was in cells <2µm, presumably unavailable to these zooplankton. Our particulate production and ingestion measurements, together with zooplankton carbon demand extrapolated from respiration estimates, suggest that the zooplankton community of Davies Reef derives much of its nutrition from detritus.Joint contribution from the University of Maryland, Center for Environmental and Estuarine Studies (No. 2015), and the Microbial Ecology on a Coral Reef Workshop (MECOR No. 19)     

Vertical distribution of fish larvae in the Great Barrier Reef Lagoon,Australia

To investigate the natural defenses of Antarctic marine organisms against exposure to ultraviolet (UV) radiation (280 to 320 nm), 57 species (1 fish, 48 invertebrates, and 8 algae) were collected during austral spring 1988 in the vicinity of Palmer Station (Anvers Island, Antarctic Peninsula) and were analyzed for the presence of mycosporine-like amino acids (MAAs), compounds that absorb UV radiation and may provide shielding from these biologically hazardous wavelengths. Nearly 90% of the 57 species examined contained MAAs, and eight specific MAA compounds were identified. Seven of these (palythine, porphyra-334, shinorine, mycosporineglycine, palythene, asterina-330, and palythinol) have been observed previously in marine organisms from temperate and tropical latitudes. A new MAA, mycosporineglycine: valine, was found in the Antarctic fish and in 38 of the invertebrate species examined. This study confirms widespread occurrence of MAAs in Antarctic marine organisms and suggests that these species have some degree of natural biochemical protection from UV exposure.Contribution No. 502 from the Australian Institute of Marine Science     

Production and reworking of sediment by parrotfishes (family Scaridae) on the Great Barrier Reef,Australia

Sediment produced by parrotfishes (family Scaridae) may comprise new bioeroded material and/or reworked sediment. The relative contribution of the two components was examined in two bioeroding Chlorurus species, C. gibbus and C. sordidus, from Lizard Island in the Northern Great Barrier Reef. The relative importance of reworked sediment was determined based on direct estimates of sediment ingestion. In C. gibbus, 2.4% of the sediment produced is reworked. In C. sordidus, reworking contributes 27.2%. Comparisons of sediment size-distributions in epilithic algal communities, gut contents and defaecation sites suggest that both C. gibbus and C. sordidus markedly decrease the particle size of sediment as a result of ingestion and trituration in the pharyngeal apparatus.     

No genetic differentiation of giant clam (Tridacna gigas) populations in the Great Barrier Reef,Australia

Six Tridacna gigas populations were sampled in 1990 from locations throughout the central and northern Great Barrier Reef (GBR). Despite separations in excess of 1000 km, mean Nei's unbiased genetic distances among the populations was 0.0007. The complete lack of spatial variation observed among populations did not results from lack of genetic variability. Genetic variation within populations was high, with mean heterozygosities from 0.221 to 0.250. Gene frequencies were consistent with expectations under conditions of Hardy-Weinberg equilibrium. These data suggest panmixis, or random mating, throughout the highly connected reef system of the central and northern GBR. The large gene exchange among the giant clam populations has important implications for conservation management of one of the few large populations of T. gigas in the world. Small local effects are likely to be overcome in time by inputs from other sources. However, large genetic perturbations, particularly from up-current sources, may spread rapidly through the population.Contribution No. 561 from the Australian Institute of Marine Science     

Occurrence and characteristics of unusual protistan symbionts from surgeonfishes (Acanthuridae) of the Great Barrier Reef,Australia

The occurrence of unusual symbiotic microorganisms was examined in the intestines of a range of fish from the Great Barrier Reef, Australia. The fish taxa examined included 26 species of the family Acanthuridae, as well as representatives of phylogenetically related and herbivorous taxa. The microorganisms, referred to as protists, were only found in herbivorous and detritivorous members of the Acanthuridae. Protists were not found in planktivorous acanthurids, nor in any members of the families Kyphosidae, Pomacentridae, Scaridae, Zanclidae, Siganidae and Bleniidae we examined. In addition, protists were absent from the herbivorous acanthurids A. xanthopterus and A. nigricans. A range of protist forms, characterized by differences in size (8 to 417 m), shape and mode of cell division (daughter-cell production and binary fission), was observed. The occurrence of these forms appeared to be correlated with host feedingecology. Large forms (>100 m) of the protists were only found in acanthurids which fed over hard-reef substrata. Smaller forms were found in sand-grazing and detritivorous species. One of the protist forms appears identical to protists previously reported from Red Sea acanthurids.     

Spatial,temporal, and behavioral patterns in emergence of zooplankton in the lagoon of Heron Reef,Great Barrier Reef,Australia

A total of 34 zooplanktonic taxa were common in emergence trap, reentry trap, and net-tow samples taken in the lagoon of Heron Reef, Great Barrier Reef, between 27 February and 22 March and between 11 June and 4 July 1985. Twenty-nine of these taxa were classified as demersal (17 taxa), meroplanktonic and larval (10 taxa), or incidental (2 taxa). The remaining five multispecific groups yielded variable results. Differences were observed between two locations separated by 200 m, with emergence 2 to 62 times greater for 22 taxa at a deeper site with larger coral formations. Most zooplankters were more common (2 to 122 times) in samples from 1 m² areas around 0.25 to 0.5 m² patches of branching coral. However, two species of copepods, Pseudodiaptomus colefaxi and Metis holothuriae, were taken in greater numbers (3 to 12 times) from open sand. Seasonal increases (2 to 322 times) were observed for 13 adult taxa and 8 classes of larvae or juveniles in the summer and for 10 adult taxa and one larval group in the winter. Fourteen of the 17 demersal taxa and 4 groups of large larvae or juveniles emerged in numbers 2 to 323 times greater during lunar quarters or new moons. In contrast, 6 larval taxa and 4 groups of small or transparent adults displayed significant emergence during full moons. Five diurnal emergence patterns were shown by 27 taxa, with patterns varying primarily among lunar periods. The variety of taxon-specific patterns observed in this study highlight a need for caution when generalizing about demersal zooplankton.     

Genetic structure of fissiparous populations of Holothuria (Halodeima) atra on the Great Barrier Reef

Allozyme variation at five polymorphic loci was surveyed in a total of 311 individuals of the sea cucumber Holothuria (Halodeima) atra (Jäger, 1833) collected from two nearshore and two midshelf populations in the Great Barrier Reef in November 1996. Strong deviations in genotype frequencies from those expected under Hardy–Weinberg equilibrium, particularly a large number of heterozygote excesses, confirmed the occurrence of asexual reproduction. Females and males differed significantly in genotype frequencies as a result of differences in either the amount of fission in each sex or in the mortality of asexually produced recruits. The estimated maximum sexual input (number of sexually produced individuals: sample size = N*:N_i) to the two nearshore reefs (38 to 67%) was low relative to that to the two midshelf reefs (74 to 87%). The three ratios and G _o :G _e , N _go :N _i , N*:N _i , (where G _o = observed genotypic diversity, G _e = expected genotypic diversity, N _go = number of genotypes) considered to be indicators of the extent of asexual reproduction, showed a consistent trend in the degree of asexual reproduction similar to that derived from the number of regenerating individuals observed in the populations for which data were available. F-statistic analyses of clonal gene frequencies demonstrated that all populations received sexual recruits from the same gene pool. There was evidence of restricted sexual recruitment to the Fantome population, suggesting that asexual reproduction was dominant only in areas where sexual recruitment was limited by other factors.     

Composition of the near-reef zooplankton at Heron Reef,Great Barrier Reef

Using a light trap, zooplankton was sampled at three stations at Heron Reef, Great Barrier Reef: (a) a typical patch reef in the Heron lagoon, (b) a site in 8 m water on the southern slope of Heron reef, and (c) a station approximately 300 m south of (b), in the open water of the channel between Heron and Wistari reefs. Samples were taken at the surface and on the substratum at the lagoon and reef-slope stations, and at 3 to 6 m depth at the open-water station. A total of 114 taxa, many recognized as species, were distinguished in the samples. Pronounced differences existed in abundance, diversity, and taxonomic composition of the samples obtained at different stations. Less pronounced differences existed between surface and substratum samples from the same station. Near-reef samples were more similar to one another than to open-water samples. Decapod larvae, amphipods, and cumaceans were all abundant in near-reef samples and very rare in open-water samples. Forams, isopods, mysids and polychaetes were common in near-reef samples, and rare or absent in open-water samples. Copepods were abundant in all samples but the near-reef samples contained predominantly different species than did samples from the open water. The near-reef fauna included 66 taxa which did not occur in open-water samples. Many of these were epibenthic rather than strictly planktonic in behaviour.     

Genetic structure of outbreaking and non-outbreaking crown-of-thorns starfish (Acanthaster planci) populations on the Great Barrier Reef

The study used population genetic data to test whether outbreaks of crown-of-thorns starfish (Acanthaster planci) on the Great Barrier Reef (GBR) are largely derived from a single outbreak or are independent events. The consequences of different modes of outbreak for population differentiation and gene flow were predicted and then compared with those estimated from a set of 8 outbreaking and a set of 5 non-outbreaking populations sampled in 1986 and 1987. The level of inter-population variation observed among outbreaking populations was less than that among non-outbreaking populations and gene flow was greater among outbreaking than among non-outbreaking populations. Greater population differentiation among non-outbreaking than outbreaking populations was not consistent with the hypothesis that outbreaks were independent events, but was consistent with a number of outbreaks being secondary. Estimates which took account of a number of aspects of sampling error demonstrated significant levels of genetic subdivision among non-outbreaking populations but not among outbreaking populations. The lack of significant genetic subdivision of outbreaking populations, given significant levels among non-outbreaking populations, was also inconsistent with outbreaks being indenpendent events, but was consistent with outbreaks being largely secondary. The allozyme data were insufficient to identify clearly individual populations that might have been the result of an independent outbreak. It is concluded that the majority of outbreaks are probably secondary derivatives from a single primary outbreak occurring in the northern part of the Central Section of the GBR, although the possibility that a small number of populations might outbreak independently of the main set cannot be excluded.Contribution No. 547 from the Australian Institute of Marine Science     

Diversity,abundance, and distribution of reef sharks on outer-shelf reefs of the Great Barrier Reef,Australia

Quantifying the distribution and habitat use of sharks is critical for understanding their ecological role and for establishing appropriate conservation and management regimes. On coral reefs, particularly the Great Barrier Reef (GBR), little is known regarding the distribution of sharks across major reef habitat types. In this study, we surveyed shark populations across outer-shelf reefs of the GBR in order to determine the diversity, abundance, and distribution of reef sharks across three major coral reef habitats: (1) the reef slope, (2) the back reef and (3) the reef flat. Model selection revealed that habitat was the principal factor influencing shark distribution and abundance. Specifically, overall shark abundance and diversity were significantly higher on the reef slope (and to a lesser degree, the back reef) than the reef flat. This confirms that shark populations are not homogeneously distributed across coral reefs. Thus, the results presented herein have important implications for shark population assessments. In addition, our results highlight the potential importance of the reef slope, with high levels of live coral cover and structural complexity, for sustaining reef shark populations. As this habitat is highly susceptible to disturbance events, this study provides a useful context for predicting and understanding how environmental degradation may influence reef shark populations in the future.     

Effects of autotomy on long-term survival and growth of painted spiny lobster (Panulirus versicolor) on the Great Barrier Reef, Australia

The effects of autotomy (shedding of appendages) on survival and growth rates of painted spiny lobster were investigated at Northwest Island (23^° 18?? S, 152^° 43?? E) during the period 2003?C2006. Adult lobsters were captured, tagged, and classified as either uninjured (n?=?68), minimally injured (n?=?39) or moderately injured (n?=?19) depending on the number and type of appendages that were autotomized during capture and handling. Six to thirty-six months after release, 86 lobsters were recaptured (mean time at large?=?305?days). Recapture rates of uninjured (64.7%), minimally injured (71.8%), and moderately injured lobsters (73.7%) were not significantly different. Similarly, mean annualized growth rates of uninjured, minimally injured, and moderately injured lobsters were not significantly different. This suggests that the energetic cost of a single episode of autotomy is either negligible or exists as a trade-off with some other life history trait, such as reduced reproductive performance. These results support the use of certain management tools (e.g., size limits) that prescribe release of non-legal lobsters, regardless of their injury status.     

Diel patterns of emergence of crinoids (Echinodermata) from within a reef at Lizard Island,Great Barrier Reef,Australia

Periods of emergence of nine species (88 individuals) of crinoids (Comanthus parvicirrus, Clarkcomanthus albinotus, Comaster multifidus, Oxycomanthus comanthipinna, Oligometra serripinna, Comanthus gisleni, Comanthus wahlbergi, Comatula purpurea, and Oxycomanthus exilis) were monitored at Lizard Island, Queensland, over seven days in March 1983. One species (O. serripinna) was fully exposed and the others partially exposed. Two patterns of emergence were species-specific: emergent both day and night, and emergent only at night. Intraspecific exposure patterns were generally synchronous in six species and asynchronous in three species. The number of species visible was relatively constant during all dives, while at least twice as many individuals were visible at night compared to day. Degree of emergence was determined as the number and length of arms extended into the water column. Except for species fully exposed, degree of crinoid emergence was generally minimal at midday and maximal at twilight and night. Increases in both number of crinoids visible, and the amount of an individual's emergence, corresponded to decreasing light intensities, even during daytime. It is suggested that the patterns of exposure are a response to increased prey abundance at twilight and night, and also a means of avoiding diurnal predators. Gonads on the longest arms of some partially exposed crinoids were not extended into the water, thus protecting the gonads from predators.     

Modelling the photosynthetic production by sponges on Davies Reef,Great Barrier Reef

Sponge populations on Australia's Great Barrier Reef (GBR) may contain a mix of both phototrophic and heterotrophic species. The distribution of many of these sponges on reefs is assumed to be determined by light. A model was developed to investigate how the distribution of phototrophic sponges over depth is restricted by the availability of photosynthetically active radiation. Estimates of the balance between photosynthetic production and the total respiratory demand of entire sponge communities on Davies Reef (a middle-shelf reef of the Great Barrier Reef) are provided. These estimates are based upon published data for community composition and biomass, whilst photokinetic parameters have been determined for a variety of sponge species from oxygenexchange measurements. Phototrophic sponges on the fore-reef slope are predicted to exist at or above a state of net 24 h compensation (i.e., photosynthetic oxygen production by sponges balances or exceeds respiration over a 24 h period) to a depth of 30 m. It is proposed that phototrophic sponges are obligate phototrophs because the availability of light for photosynthesis corresponds with the lower depth limit of their distribution. Sponge communities (including both phototrophs and heterotrophs) from the fore-reef and lagoon exist close to a state of net 24 h compensation to a depth of 10 to 15 m. This balance shows diurnal variations, associated with the activity of phototrophs, such that instantaneous compensation of the community may occur to depths of 20 to 25 m when light is maximal.     

Nitrogen excretion by some demersal macrozooplankton in Heron and One Tree Reefs,Great Barrier Reef,Australia

Nitrogen excretion rates of demersal macrozooplankton were measured together with nitrogen concentrations in the water column and sediments in lagoons of Heron Reef and One Tree Reef, Great Barrier Reef, Australia, during August and November 1991. Excretion rates increased with body weight, and weight-specific excretion rates of the demersal macrozooplankton were comparable to those of pelagic zooplankton and meiofauna in the Great Barrier Reef. Values of demersal macrozooplankton abundance from previous studies and excretion rates from this study were combined to estimate fluxes of ammonium from demersal macrozooplankton in coral reef lagoons. The estimated fluxes in the water column and sediments were 12 M NH₄ m^-2 d^-1 and 34 M NH₄ m^-2d^-1, respectively. These fluxes were compared with reported fluxes of ammonium in coral reef lagoons in the Great Barrier Reef, Australia. The estimated flux from the demersal macrozooplankton in the water column was 29 and 9% of those reported for microheterotroph regeneration and phytoplankton utilization, respectively. It was 10% of the reported advective flux during periods of low advection and 13% of the maximum efflux from sediments computed from diffusion models. The estimated flux from the demersal macrozooplankton in the sediments exceeded those reported for meiofauna, and was 5 to 32% and 2 to 13% of those reported for ammonification and utilization in sediments, respectively. The potential importance of demersal macrozooplankton in mediating sediment-water column exchanges in the absence of diffusive effluxes and when they swarm is discussed.     

Zoning,a fundamental cornerstone of effective Marine Spatial Planning: lessons learnt from the Great Barrier Reef,Australia

The Great Barrier Reef Marine Park was established to provide for conservation and ecologically sustainable multiple use of 344,400 km² of a large marine ecosystem. Management is based on multiple use, with zoning as a fundamental component of marine spatial planning. The legislative framework, including a specific Act and Regulations, address the objectives of ecosystem-based, integrated management of human uses and impacts consistent with best contemporary understanding of biological diversity. Zoning is one of a suite of management tools that include other spatial and temporal management tools and non-spatial measures including public education, community engagement, codes of environmental best practice, industry partnerships and economic instruments. The first section of the Great Barrier Reef Marine Park came into operation in 1981 and the most recent zoning came into operation in mid 2004. The paper discusses some common misunderstandings about zoning and identifies lessons that appear relevant for others addressing management and use of marine ecosystems and natural resources.     

Dietary overlap among coral-feeding butterflyfishes (Chaetodontidae) at Lizard Island,northern Great Barrier Reef

This study documented the range of corals, and other prey types, consumed by 20 species of butterflyfishes, which co-occur at Lizard Island, northern Great Barrier Reef, Australia. Six species (Chaetodon aureofasciatus, C. baronessa, C. lunulatus, C. plebius, C. rainfordi and C. trifascialis) fed almost exclusively on scleractinian corals, and a further eight species (C. citrinellus, C. kleinii, C. lunula, C. melannotus, C. rafflesi, C. speculum, C. ulietensis, and C. unimaculatus) took a significant proportion of their bites from corals. The other six species (C. auriga, C. ephippium, C. lineolatus, C. semeion, C. vagabundus, and Chelmon rostratus) rarely consumed coral, but fed on small discrete prey items from non-coral substrates. Coral-feeding butterflyfishes consumed a wide range of corals. Chaetodon lunulatus, for example, consumed 51 coral species from 24 different genera. However, there was up to 72% dietary overlap between coral-feeding butterflyfishes, with 11/14 species feeding predominantly on Acropora hyacinthus or Pocillopora damicornis. The most specialised corallivore, C. trifascialis, took 88% of bites from A. hyacinthus. Chaetodon trifascialis defend territories encompassing one or more colonies of A. hyacinthus, and may have prevented other species such as C. lunulatus from feeding even more extensively on this coral. This study has shown that coexistence of coral-feeding butterflyfishes occurs despite an apparent lack of partitioning of prey resources. While different coral-feeding butterflyfishes were more or less selective in their use of different coral prey, virtually all species fed predominantly on A. hyacinthus or P. damicornis.Electronic Supplementary Material Supplementary material is available for this article at     

Allozyme electrophoresis indicates high gene flow between populations of Holothuria (Microthele) nobilis (Holothuroidea: Aspidochirotida) on the Great Barrier Reef

 Genetic variation in 15 Holothuria (Microthele) nobilis (Selenka, 1867) populations on the Great Barrier Reef was studied at seven polymorphic allozyme loci. Although populations were separated by distances up to 1300 km, there were no apparent restrictions to gene flow (F _ST values were not significantly different from 0) and the maximum Nei's unbiased genetic distance was 0.003. Populations were in Hardy–Weinberg equilibrium at all loci. The estimated maximum sexual input [this is the ratio of the number of sexually produced individuals (N*) to the sample size (N _i )] and the minimum sexual input [this is the ratio of the number of genotypes (N _go ) over the sample size (N _i )] were used as estimators for the amount of asexual reproduction. Both parameters suggested that H. nobilis reproduces solely by sexual means (N*:N _i : = 1; N _go :N _i  = 0.74 to 1). The allozyme data indicated high gene flow between populations, but the possibility that allozyme frequencies may not be at equilibrium means that it was not possible to distinguish whether the patterns reflect present-day dispersal or dispersal that occurred in the past. Received: 27 March 2000 / Accepted: 29 June 2000     

Coral-spawn slicks in the Great Barrier Reef: preliminary observations

Aerial surveys and surface samples in the spring of 1985, showed that slicks of coral eggs and embryos (coral spawn) formed in large numbers within and between reefs in the Central Great Barrier Reef Region. Coral-spawn slicks appeared on the days immediately following the annual mass multispecific spawning of reef corals. They were white or pink in colour, and were often highly elongate in form extending up to 5 km in length, and 10 m in width. Over 99% of each slick sampled during the surveys consisted of dead eggs, embryos and their breakdown products, which formed dense, highly viscous patches readily recognizable during aerial surveys. Despite the low proportion of live material, the slicks contained high concentrations of live embryos (15 to 230 per litre) which were over two orders of magnitude greater than concentrations in adjacent water masses. The distinctive colour, shape and texture of the coral-spawn slicks generally distinguished them from slicks formed by blooms of the blue-green alga Oscillatoria erythraea, which also occur commonly in the region. Many of the slicks were closely associated with surface oceanographic features, such as fronts between water parcels, and wakes and eddies behind reefs. Although more detailed sampling and surveys are required, these results suggest that it may be possible to track the movements of coral embryos and larvae directly for the first one or two days following mass spawning, and indirectly thereafter by monitoring other surface features.