Picoplankton dynamics in Davies Reef lagoon, the Great Barrier Reef, Australia

The diel variations in abundance and frequency of dividing cells(FDC) of coccoid cyanobacteria in a coral reef lagoon were investigatedin June, September and December 1989, and April 1990. Cyanobacteriaand picoplanktonic eukaryotes (<3 µm) were sampledmonthly from January to December 1990. The average abundancesof cyanobacteria and eukaryotes ranged between 1.17–10.0610⁴cells ml^–1 and 0.16–2.4110⁴ cells ml^–1, respectively,with abundances of both being higher in summer (November-April)than in winter (May-October). The ratio of cyanobacteria toeukaryotes fluctuated from 1.93 to 8.67, independent of theseasonal variation in their abundances. The instantaneous growthrate of cyanobacteria, which was estimated from the daytimeabundance increment, ranged between 0.430 and 3.144 day^–1The estimated daily specific growth rate of cyanobacteria bythe FDC method ranged between 0.231 and 0.966 day^–1. InApril, despite the high specific growth rate and low flushingconditions. cyanobacterial abundance showed a cyclic diel pattern,suggesting a strong grazing impact on their population.     

The Diversity of Coolia spp. (Dinophyceae Ostreopsidaceae) in the Central Great Barrier Reef Region

Background

Dinoflagellates are important primary producers, crucial in marine food webs. Toxic strains, however, are the main causative agents of non-bacterial seafood poisoning, a major concern for public health worldwide. Despite their importance, taxonomic uncertainty within many genera of dinoflagellates is still high. The genus Coolia includes potentially harmful species and the diversity within the genus is just starting to become apparent.

Methodology/Principal Findings

In the current study, cultures were established from strains of Coolia spp. isolated from the central Great Barrier Reef (GBR). Cultures were identified based on thecal plate morphology and analyses of sequences (18S, ITS and 28S) from the nuclear rRNA operon. We report that the central GBR harbors a high diversity of Coolia species, including two species known to be capable of toxin production (C. tropicalis and C. malayensis), as well as the non-toxic C. canariensis. The strain of C. canariensis isolated from the GBR may in fact be a cryptic species, closely related but nevertheless phylogenetically distinct from the strain on which the holotype of C. canariensis was based. We also found evidence of the occurrence of a cryptic species morphologically very similar to both C. malayensis and C. monotis. The consequences of taxonomic confusion within the genus are discussed.

Conclusion/Significance

The central GBR region harbors a previously unreported high diversity of Coolia spp., including two species known to potentially produce toxins. The presence of a cryptic species of unknown toxicity highlights the importance of cryptic diversity within dinoflagellates.     

Coral Reef Community Composition in the Context of Disturbance History on the Great Barrier Reef,Australia

Much research on coral reefs has documented differential declines in coral and associated organisms. In order to contextualise this general degradation, research on community composition is necessary in the context of varied disturbance histories and the biological processes and physical features thought to retard or promote recovery. We conducted a spatial assessment of coral reef communities across five reefs of the central Great Barrier Reef, Australia, with known disturbance histories, and assessed patterns of coral cover and community composition related to a range of other variables thought to be important for reef dynamics. Two of the reefs had not been extensively disturbed for at least 15 years prior to the surveys. Three of the reefs had been severely impacted by crown-of-thorns starfish outbreaks and coral bleaching approximately a decade before the surveys, from which only one of them was showing signs of recovery based on independent surveys. We incorporated wave exposure (sheltered and exposed) and reef zone (slope, crest and flat) into our design, providing a comprehensive assessment of the spatial patterns in community composition on these reefs. Categorising corals into life history groupings, we document major coral community differences in the unrecovered reefs, compared to the composition and covers found on the undisturbed reefs. The recovered reef, despite having similar coral cover, had a different community composition from the undisturbed reefs, which may indicate slow successional processes, or a different natural community dominance pattern due to hydrology and other oceanographic factors. The variables that best correlated with patterns in the coral community among sites included the density of juvenile corals, herbivore fish biomass, fish species richness and the cover of macroalgae. Given increasing impacts to the Great Barrier Reef, efforts to mitigate local stressors will be imperative to encouraging coral communities to persist into the future.     

Patterns in the distribution of fish communities across the Central Great Barrier Reef

Summary Changes in the structure of fish communities along a transect from the Australian mainland to the Coral Sea, in the Central region of the Great Barrier Reef, were examined. Visual censuses of fish were made on the outer reef slopes (0 to 13 m deep) of two inshore reefs, approximately 10 km offshore, three reefs on the mid-shelf, 50 km offshore, three reefs on the outer shelf, 100 km offshore, and three reefs in the Coral Sea approximately 200 km offshore. The Pomacentridae, Chaetodontidae, Acanthuridae and Scaridae were examined in detail—the Labridac, Siganidae and the lutjanid genus Caesio in less detail. Major changes in the composition of fish communities occurred along the transect (Fig. 3). There were differences in the composition of assemblages among replicate censuses within individual reefs and also differences between reefs at the same location on the transect but these differences were small compared to those among locations. The nature of the distribution of species across the transect differed between families (Figs. 4–6). Pomacentrid and chaetodontid species were significantly more restricted in distribution than acanthurids, scarids or labrids.     

Assessment of the eutrophication status of the Great Barrier Reef lagoon (Australia)

Current scientific consensus is that inshore regions of the central and southern Great Barrier Reef, Australia, are at risk of impacts from increased nutrient (as well as sediment and pesticide) loads delivered to Reef waters. Increases in the discharge of water quality contaminants to the Reef are largely a consequence of the expansion of agricultural practices in northern Queensland catchments following European settlement in the 1850s. In particular, the presence of elevated chlorophyll a and nutrient concentrations in many parts of the inshore Great Barrier Reef together with intense and extensive phytoplankton blooms following the discharge of nutrient-rich river flood waters suggest that the central and southern inshore area of the Great Barrier Reef is likely to be significantly impacted by elevated nutrient loads. The biological consequences of this are not fully quantified, but are likely to include changes in reef condition including hard and soft coral biodiversity, macroalgal abundance, hard coral cover and coral recruitment, as well as change in seagrass distribution and tissue nutrient status. Contemporary government policy is centered around promotion and funding of better catchment management practices to minimize the loss of catchment nutrients (both applied and natural) and the maintenance of a Reef wide water quality and ecosystem monitoring program. The monitoring program is designed to assess trends in uptake of management practice improvements and their associated impacts on water quality and ecosystem status over the next 10 years. A draft set of quantitative criteria to assess the eutrophication status of Great Barrier Reef waters is outlined for further discussion and refinement.     

New and noteworthy plants from Great Barrier Reef sand cays,Australia

Observations are presented on new and critical plants from the northern sand cays on the Great Barrier Reef, Queensland, Australia, based mainly on recent collections made by David R. Stoddart and Ralf Buckley. New species and varieties are described:Lepturus stoddartii (Poaceae),Boerhavia fistulosa var.fistulosa and var.puberuliflora (Nyctaginaceae),Boerhavia albiflora var.heronensis, Spermacoce everistiana (Rubiaceae), andSpermacoce buckleyi; a new combination is made:Diospyros ferrea var.compacta (R. Br.) (Ebenaceae); and additional taxonomic notes are given onBoerhavia, Euphorbia (Euphorbiaceae), andAbutilon (Malvaceae).     

Laboratory culture studies of Trichodesmium isolated from the Great Barrier Reef Lagoon, Australia

Cultures of Trichodesmium from the Northern and Southern Great Barrier Reef Lagoon (GBRL) have been established in enriched seawater and artificial seawater media. Some cultures have been maintained with active growth for over 6years. Actively growing cultures in an artificial seawater medium containing organic phosphorus (glycerophosphate) as the principal source of phosphorus have also been established. Key factors that contributed to the successful establishment of cultures were firstly, the seed samples were collected from depth, secondly, samples were thoroughly washed and thirdly, incubations were conducted under relatively low light intensities (PAR 40–50molquantam^–2s^–1). N₂ fixation rates of the cultured Trichodesmium were found to be similar to those measured in the GBRL. Specific growth rates of the cultures during the exponential growth phase in all enriched media were in the range 0.2–0.3day^–1 and growth during this phase was characterised by individual trichomes (filaments) or small aggregations of two to three trichomes. Characteristic bundle formation tended to occur following the exponential growth phase, which suggests that the bundle formation was induced by a lack of a necessary nutrient e.g. Fe. Results from some exploratory studies showed that filament-dominated cultures of Trichodesmium grew over a range of relatively low irradiances (PAR 5–120molquantam^–2s^–1) with the maximum growth occurring at 40–50molquantam^–2s^–1. These results suggest that filaments of the tested strain are well adapted for growth at depth in marine waters. Other studies showed that growth yields were dependent on salinity, with maximum growth occurring between 30 and 37psu. Also the cell yields decreased by an order of magnitude with the reduction of Fe additions from 450 to 45nM. No active growth was observed with the 4.5nM Fe addition.     

Benthic microalgae in coral reef sediments of the southern Great Barrier Reef,Australia

The abundance and productivity of benthic microalgae in coral reef sediments are poorly known compared with other, more conspicuous (e.g. coral zooxanthellae, macroalgae) primary producers of coral reef habitats. A survey of the distribution, biomass, and productivity of benthic microalgae on a platform reef flat and in a cross-shelf transect in the southern Great Barrier Reef indicated that benthic microalgae are ubiquitous, abundant (up to 995.0 mg chlorophyll (chl) a m^–2), and productive (up to 110 mg O₂ m^–2 h^–1) components of the reef ecosystem. Concentrations of benthic microalgae, expressed as chlorophyll a per surface area, were approximately 100-fold greater than the integrated water column concentrations of microalgae throughout the region. Benthic microalgal biomass was greater on the shallow water platform reef than in the deeper waters of the cross-shelf transect. In both areas the benthic microalgal communities had a similar composition, dominated by pennate diatoms, dinoflagellates, and cyanobacteria. Benthic microalgal populations were potentially nutrient-limited, based on responses to nitrogen and phosphorus enrichments in short-term (7-day) microcosm experiments. Benthic microalgal productivity, measured by O₂ evolution, indicated productive communities responsive to light and nutrient availability. The benthic microalgal concentrations observed (92–995 mg chl a m^–2) were high relative to other reports, particularly compared with temperate regions. This abundance of productive plants in both reef and shelf sediments in the southern Great Barrier Reef suggests that benthic microalgae are key components of coral reef ecosystems.Communicated by Environmental Editor, B.C. Hatcher     

Benthic diatom community composition in three regions of the Great Barrier Reef,Australia

Despite their ecological importance, very little is known about the taxonomy and ecology of benthic diatoms in coral-reef ecosystems. Diatom densities and community compositions were investigated in three distinct regions of the Great Barrier Reef (GBR): (a) Wet Tropics (WT), (b) Princess Charlotte Bay (PCB), and (c) the Outer Shelf (OS). About 209 taxa were observed in the GBR sediments studied, with an average abundance of 2.55 × 10⁶ cells ml⁻¹ in the upper 1 cm of sediment. Total diatom abundances were about twice as high in inshore reefs of PCB and WT compared with OS reefs. A redundancy analysis (RDA) of diatom composition clearly grouped the three regions separately but showed little influence of grain size, nitrogen and organic carbon content of the sediments. The only distinct correlates were inorganic carbon and the distance to the mainland associated with OS communities. Analysis of similarity (ANOSIM) of diatom community composition revealed significant differences between all three regions. Indicator values showed that most highly abundant taxa occurred in all regions. However, several taxa were clearly identified as characteristic of particular regions. It is hypothesised that variations in nutrient and light availability are the most likely explanation for the observed differences in community composition.     

Reproduction of the inshore coral trout Plectropomus maculates (Perciformes: Serranidae) from the Central Great Barrier Reef, Australia

The reproductive biology of the serranid fish Plectropomus maculatus sampled from inshore waters of the Central Great Barrier Reef was studied based on histological analyses of gonad material. This species was shown to be a monandric protogynous hermaphrodite. The process of sex change foliowed the spawning period observed during September through November. Plectropomus: maculatus showed multiple spawning during this period. Sex change followed the usual protogynous mode with degeneration of ovarian germinal tissue accompanied by proliferation of male germinal tissue in the gonad. The sex structure of the sampled population was analysed based on age and size information. The size and age of first reproduction for females was 30.0cm s. L. and 2 years of age. The size and age of sex-transition was 35.4 cm s. L. and 4.4 years of age. The sex/size and sex/age relationships indicated that sex-change can occur over a broad range of sizes and ages. The sizes and age distributions of males and females P. maculates overlapped over 38% of the length range and over 42% of the maximum age observed.     

Genetic structure of a reef-building coral from thermally distinct environments on the Great Barrier Reef

Adaptation to localised thermal regimes is facilitated by restricted gene flow, ultimately leading to genetic divergence among populations and differences in their physiological tolerances. Allozyme analysis of six polymorphic loci was used to assess genetic differentiation between nine populations of the reef-building coral Acropora millepora over a latitudinal temperature gradient on the inshore regions of the Great Barrier Reef (GBR). Small but significant genetic differentiation indicative of moderate levels of gene flow (pairwise F _ST 0.023 to 0.077) was found between southern populations of A. millepora in cooler regions of the GBR and the warmer, central or northern GBR populations. Patterns of genetic differentiation at these putatively neutral allozyme loci broadly matched experimental variation in thermal tolerance and were consistent with local thermal regimes (warmest monthly-averages) for the A. millepora populations examined. It is therefore hypothesized that natural selection has influenced the thermal tolerance of the A. millepora populations examined and greater genetic divergence is likely to be revealed by examination of genetic markers under the direct effects of natural selection.     

Some nemerteans (Nemertea) from Queensland and the Great Barrier Reef, Australia

Three species of marine nemerteans described and illustrated from Queensland and the Great Barrier Reef, Australia, include one new genus and two new species: these are the monostiliferous hoplonemerteans Thallasionemertes leucocephala gen. et sp. nov. and Correanemertes polyophthalma sp. nov. A new colour variety of the heteronemertean Micrura callima is also reported, this species previously only being known from Rottnest Island, Western Australia. A key for the field identification of the marine nemerteans recorded from coastal Queensland and the Great Barrier Reef is provided.     

Submerged reefs and terraces on the shelf edge of the Great Barrier Reef,Australia

The morphology and distribution of seabed features on the shelf edge and upper slope adjacent to the Great Barrier Reef, Australia, has been examined using shallow seismic profiling, side-scan sonar and precision echo sounding data, supplemented by submersible investigations. The data reveal a submerged barrier reef system at different locations between 15° 45 S and 21° 00 S. At two locations, an extensive offshore platform rising above the 50 m isobath and extending for over 20 km parallel to the shelf edge is backed by a relict lagoon at an average depth of 75 m. In addition, outer shelf and upper slope terraces are found at many depths; however, only some occur consistently throughout the region while most others occur only locally. Frequency distributions indicate the greatest occurrence of features at depths of 44–46, 60–66, 72–78, 80–84, 102–106 and 146–148 m. Caution should be exercised when interpreting these features with respect to specific lower sea level stands.     

Epibenthie fish larvae in the Great Barrier Reef Lagoon near Lizard Island,Australia

Epibenthic fish larvae near Lizard Island in the Great Barrier Reef Lagoon were sampled with a plankton sled during daylight in November 1981 and January–February 1982. Abundance in the epibenthos was highly variable, and although many types of larvae were present, few were concentrated there relative to the water column. Among those taxa concentrated in the epibenthos, abundances were low and variances were high. Larvae of bregmacerotids, callionymids, clupeids, monacanthids, pinguipedids, platycephalids, pseudochromids, and especially schindleriids, leiognathids and terapontids were concentrated in the epibenthos. Few reef fish larvae were epibenthic. There was some evidence of diel and ontogenetic movements into and out of the epibenthos. Our limited sampling indicates that conventional midwater plankton sampling is adequate for most fish larvae found in the Lizard Island area, but for the larvae of the above ten families, this could produce large underestimates of abundance.     

Halimeda bioherms of the northern Great Barrier Reef

The reefless tract directly behind the ribbon reefs on the outer shelf off Cooktown supports a luxuriant growth of Halimeda that, during the Holocene, has developed into bioherms. These mounded biodies of unconsolidated sediment have formed banks that vary in height between 2 and 20 m. Combined shallow, high-resolution seismic reflection profiles and side-scan sonar have diferentiated three areas of biohermal complexes behind the ribbon reefs of Cooktown. Observations by SCUBA and submersible plus the sedimentology of the bioherms indicate that they are in situ accumulations. Evidence from dating of cores suggests that the Halimeda bioherms began to grow about 10 000 years B.P. and their growth has continued to the present time, even though their tops are presently restricted to a depth of -20 m. It is suggested that the origin and morphology of the bioherms are related to a specific hydrodynamic phenomenon, involving jets of nutrient-rich, upwelled oceanic water intruding onto the outer shelf via the narrow passes between the ribbon reefs, and forming eddies behind the ribbons.     

Structural and Psycho-Social Limits to Climate Change Adaptation in the Great Barrier Reef Region

Adaptation, as a strategy to respond to climate change, has limits: there are conditions under which adaptation strategies fail to alleviate impacts from climate change. Research has primarily focused on identifying absolute bio-physical limits. This paper contributes empirical insight to an emerging literature on the social limits to adaptation. Such limits arise from the ways in which societies perceive, experience and respond to climate change. Using qualitative data from multi-stakeholder workshops and key-informant interviews with representatives of the fisheries and tourism sectors of the Great Barrier Reef region, we identify psycho-social and structural limits associated with key adaptation strategies, and examine how these are perceived as more or less absolute across levels of organisation. We find that actors experience social limits to adaptation when: i) the effort of pursuing a strategy exceeds the benefits of desired adaptation outcomes; ii) the particular strategy does not address the actual source of vulnerability, and; iii) the benefits derived from adaptation are undermined by external factors. We also find that social limits are not necessarily more absolute at higher levels of organisation: respondents perceived considerable opportunities to address some psycho-social limits at the national-international interface, while they considered some social limits at the local and regional levels to be effectively absolute.     

Role of plankton in the turnover of organic matter on the Great Barrier Reef,Australia

Number, biomass and production of phytoplankton, bacteria, micro- and mesozooplankton and turnover of labile and stable organic matter were measured in waters over some Capricornia round reefs, and over the reefs of Lizard Island. Primary production was 10 to 40 mg C m^–3 d^–1 but was lower over the living reefs. Microbial wet biomass in reef waters varied from 100 to 500 mg m^–3, and production from 4 to 68 mg C m^–3 d^–1, which was commensurable with primary production. The biomass of microzooplankton (ciliates, zooflagellates and larvae) in waters of Lizard Island reefs reached 100–300 mg m^–3. Mesozooplankton biomass at night in reef waters of Heron Island varied from 200 to 800 mg m^–3. Its composition depended upon the tide phase. PB coefficients in bacterioplankton were 0.3 to 1.2 per day. The food demand of bacterioplankton in waters over the reefs was 5 to 20 times higher than the primary phytoplankton production. Labile organic matter (LOM) doubled in waters after it stayed over living reef for several hours. The turnover time of LOM in reef waters was as short as 1–2 weeks.     

Diversity of Scleractinia and Octocorallia in the mesophotic zone of the Great Barrier Reef, Australia

Mesophotic coral reefs in the Indo-West Pacific, the most diverse coral reef region on earth, are among the least documented. This study provides the first detailed investigation of the diversity of Scleractinia and Octocorallia of the mesophotic Great Barrier Reef (GBR). Specimens were collected by 100-m rock dredge tows at 47–163 m depth on 23 sites in four regions (15.3°–19.7° latitude South). Twenty-nine hard coral species from 19 families were recorded, with the greatest diversity found at <60 m depth, and no specimen was found >102 m. Many of these species are also commonly observed at shallower depths, particularly in inshore areas. Twenty-seven octocoral genera were collected, 25 of which represented azooxanthellate genera. Generic richness of octocorals was highest at depths >60 m. Sixteen of the 25 azooxanthellate genera were either absent or very rare at <18 m, and only five azooxanthellate genera were common on both shallow and mesophotic reefs. Species-area models indicated that the total diversity of hard corals on the deep mesophotic reefs sampled during this study was ~84 species while octocorals were represented by ~37 genera; however, the wide 95% confidence limits indicates that more intensive sampling effort is required to improve the accuracy of these estimates. Nonetheless, these results show that the taxonomic richness, particularly of hard corals, on mesophotic reefs may be much higher than previously thought, a finding that has implications for the comprehensive and adequate protection of the full range of biodiversity of the GBR.     

Sensitivity of coral cays to climatic variations,southern Great Barrier Reef,Australia

Analysis of available wind data for the years 1962–80 from Heron Island which is located within the southern Great Barrier Reef indicates that the annual wind energy vector has oscillated within a 45 degree arc from the SSE in the early 1960's to ESE in the late 1970's. Such changes in wind direction influence the direction of propagation of the waves which mould the shape of coral sand cays in this region. Documentation is provided which shows that the variability of the shoreline positions on Erskine Island, an uninhabited vegetated sand cay reflects this change. The implication is that contemporary shoreline erosion on Heron Island is not caused by the development associated with the tourist resort there. It is a symptom of the change in the propagation direction of the wind-induced waves which is related to long-term climatic change.