Thermal stress responses in the bacterial biosphere of the Great Barrier Reef sponge,Rhopaloeides odorabile

Marine sponges are diverse, abundant and provide a crucial coupling point between benthic and pelagic habitats due to their high filtration rates. They also harbour extensive microbial communities, with many microbial phylotypes found exclusively in sponge hosts and not in the seawater or surrounding environment, i.e. so‐called sponge‐specific clusters (SCs) or sponge‐ and coral‐specific clusters (SCCs). We employed DNA (16S rRNA gene) and RNA (16S rRNA)‐based amplicon pyrosequencing to investigate the effects of sublethal thermal stress on the bacterial biosphere of the Great Barrier Reef sponge Rhopaloeides odorabile. A total of 8381 operational taxonomic units (OTUs) (97% sequence similarity) were identified, affiliated with 32 bacterial phyla from seawater samples, 23 bacterial phyla from sponge DNA extracts and 18 bacterial phyla from sponge RNA extracts. Sublethal thermal stress (31°C) had no effect on the present and/or active portions of the R. odorabile bacterial community but a shift in the bacterial assemblage was observed in necrotic sponges. Over two‐thirds of DNA and RNA sequences could be assigned to previously defined SCs/SCCs in healthy sponges whereas only 12% of reads from necrotic sponges could be assigned to SCs/SCCs. A rapid decline in host health over a 1°C temperature increment suggests that sponges such as R. odorabile may be highly vulnerable to the effects of global climate change.     

Sponge distribution across Davies Reef,Great Barrier Reef,relative to location,depth, and water movement

Sponge populations were surveyed at different depths in three zones of Davies Reef, a large platform reef of the central Great Barrier Reef. Depth is the major discriminatory factor as few sponges are found within the first 10 m depth and maximal populations occur between 15 m and 30 m on fore-reef, lagoon and back-reef slopes. Reef location is another major factor, with the lagoon containing a significantly different sponge population to either the fore-reef or the back-reef slopes. Physical factors are considered to be the major influences behind these patterns. Physical turbulence is strongest within the first 10 m and apparently limits sponge growth within these shallow zones. Insufficient photosynthetic radiation limits the growth of the sponge population below 30 m depth as many of the species are phototrophic with a dependence on cyanobacterial symbionts for nutrition. Sponge populations on the outer (fore- and back-) reef slopes are comparable with each other but different from those on lagoon slopes where currents are reduced and fine sediment loads are higher. The largest populations occur on the back-reef slope where currents are stronger and there are possibly higher concentrations of organic nutrients originating from the more productive shallow parts of the reef. While there are correlations between sponge populations and environmental parameters, data are insufficient to enable more definitive conclusions to be drawn. Most sponge species are distributed widely over the reef, however, some are restricted to a few habitats and, hence, may be used to characterize those habitats.     

Towards protecting the Great Barrier Reef from land‐based pollution

The Great Barrier Reef (GBR) is an iconic coral reef system extending over 2000 km along the north‐east coast of Australia. Global recognition of its Outstanding Universal Value resulted in the listing of the 348 000 km² GBR World Heritage Area (WHA) by UNESCO in 1981. Despite various levels of national and international protection, the condition of GBR ecosystems has deteriorated over the past decades, with land‐based pollution from the adjacent catchments being a major and ongoing cause for this decline. To reduce land‐based pollution, the Australian and Queensland Governments have implemented a range of policy initiatives since 2003. Here, we evaluate the effectiveness of existing initiatives to reduce discharge of land‐based pollutants into the waters of the GBR. We conclude that recent efforts in the GBR catchments to reduce land‐based pollution are unlikely to be sufficient to protect the GBR ecosystems from declining water quality within the aspired time frames. To support management decisions for desired ecological outcomes for the GBR WHA, we identify potential improvements to current policies and incentives, as well as potential changes to current agricultural land use, based on overseas experiences and Australia's unique potential. The experience in the GBR may provide useful guidance for the management of other marine ecosystems, as reducing land‐based pollution by better managing agricultural sources is a challenge for coastal communities around the world.     

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.     

Reproductive biology of a new hesionid polychaete from the Great Barrier Reef

We describe Lizardia hirschi, a new hesionid genus and species, from shallow water on the Great Barrier Reef. It is characterized by small size (maximally around 2 mm long) and by males with paired penes on the last segment or the pygidium. The sperm are elongated, with a conical acrosome; extended, cylindrical nucleus; and three mitochondria. The females have three to four pairs of eggs in segments 10-13, up to 150 microm in diameter. The female reproductive system consists of spermathecae, situated in the notopodia of segments 10-12, and oviducts opening ventrally on segment 11. Fertilization may be internal. The female (but not the male) reproductive system appears to be homologous to that in another small hesionid, capricornia. The phylogenetic position of L. hirschi within Hesionidae is currently uncertain due to the retention of many apparently larval features in the adults.     

Detection and Phylogenetic Analysis of Novel Crenarchaeote and Euryarchaeote 16S Ribosomal RNA Gene Sequences from a Great Barrier Reef Sponge

The presence of Archaea in the Great Barrier Reef marine sponge Rhopaloeides odorabile was investigated by 16S ribosomal RNA community analysis of total DNA extracted from the sponge tissue. The 16S rRNA gene sequences corresponding to group I crenarchaeotes and group II euryarchaeotes were recovered from R. odorabile tissue. The location of archaeal cells within the sponge tissue was investigated using fluorescently labeled oligonucleotide probes. The presence of Archaea was confirmed within all regions of the sponge tissue from R. odorabile, with a significantly higher number of archaeal cells located in the pinacoderm than the mesohyl region. This is the first report of euryarchaeaotes associated with marine sponges. Received April 16, 2001; accepted June 27, 2001     

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).     

Oxygen detoxification in algal-invertebrate symbioses from the Great Barrier Reef

Summary Examination of 34 species of symbiotic invertebrates in four phyla has confirmed the generality of a direct relationship between chlorophyll concentration and the activities of superoxide dismutase and catalase, two enzymes involved in the detoxification of active oxygen. On a finer scale, activities of these enzymes also depend on the localization of the algal symbions (intracellular or extracellular) and hence on the extent to which photosynthetic O₂ actually contacts animal cytoplasm, and on the solar irradiance experienced by the symbionts. Differences in SOD activity among organs of Tridacna crocea are not fully explained by local O₂ levels but are further related to organ-specific retes of O₂ consumption. This result is discussed in terms of known mechanisms of superoxide radical production in mitochondria and differences in O₂ utilization concentrations among various organs in bivalve molluscs.     

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.     

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.     

Internal structure and Holocene evolution of One Tree Reef,southern Great Barrier Reef

Summary Analysis of core from six drill holes and ten vibrocores from One Tree Reef has delineated five major biosedimentological facies: algal pavement, coral head facies, branching coral facies, reef flat rubble facies and sand facies. Holocene growth began around 8,000 years B.P. with a high energy coral head facies on windward margins and a lower energy branching coral facies on patch reefs and on leeward margins. Vertical accumulation rates for these two principal facies are not greatly different; the coral head facies grew at 1.8–7.3 m/1,000 years and the branching coral facies at 0.6–8.3 m/1,000 years. Growth was initially much slower than the rate of sea level rise, a situation which changed only after sea level stabilized around 6,200 years B.P. A facies evolution model with rigidly imposed time constraints divides growth into three phases, i.e. vertical growth to sea level, transitional adjustment of biofacies at sea level, and leeward progradative phases.     

The ecology of 'Acroporid white syndrome', a coral disease from the southern Great Barrier Reef

Outbreaks of coral disease have increased worldwide over the last few decades. Despite this, remarkably little is known about the ecology of disease in the Indo-Pacific Region. Here we report the spatiotemporal dynamics of a coral disease termed 'Acroporid white syndrome' observed to affect tabular corals of the genus Acropora on the southern Great Barrier Reef. The syndrome is characterised by rapid tissue loss initiating in the basal margins of colonies, and manifests as a distinct lesion boundary between apparently healthy tissue and exposed white skeleton. Surveys of eight sites around Heron Reef in 2004 revealed a mean prevalence of 8.1±0.9%, affecting the three common species (Acropora cytherea, A. hyacinthus, A. clathrata) and nine other tabular Acropora spp. While all sizes of colonies were affected, white syndrome disproportionately affected larger colonies of tabular Acroporids (>80 cm). The prevalence of white syndrome was strongly related to the abundance of tabular Acroporids within transects, yet the incidence of the syndrome appears unaffected by proximity to other colonies, suggesting that while white syndrome is density dependant, it does not exhibit a strongly aggregated spatial pattern consistent with previous coral disease outbreaks. Acroporid white syndrome was not transmitted by either direct contact in the field or by mucus in aquaria experiments. Monitoring of affected colonies revealed highly variable rates of tissue loss ranging from 0 to 1146 cm(-2) week(-1), amongst the highest documented for a coral disease. Contrary to previous links between temperature and coral disease, rates of tissue loss in affected colonies increased threefold during the winter months. Given the lack of spatial pattern and non-infectious nature of Acroporid white syndrome, further studies are needed to determine causal factors and longer-term implications of disease outbreaks on the Great Barrier Reef.     

Trace and minor element ratios inHalimeda aragonite from the Great Barrier Reef

The calcareous green algaHalimeda can be a substantial contributor to aragonite sediment in reef ecosystems. In contrast to coral aragonite, little is known about the trace and minor element composition ofHalimeda aragonite, so it is difficult to test oceanographic hypotheses about factors controlling its past growth. We investigated adapting trace element cleaning protocols for modern and HoloceneHalimeda aragonite, modern and HoloceneHalimeda trace and minor element compositions, and the potential utility ofHalimeda aragonite for paleoceanographic investigations. We successfully adapted and applied sample treatment protocols developed for measuring trace elements in coral aragonite (generally less than 500 y old) toHalimeda aragonite (modern to approximately 5000 y old in this study). ModernHalimeda aragonite from John Brewer Reef in the Central GBR had mean Cd/Ca ratios of 5.19 ± 1.68 nmol/mol forHalimeda micronesica and 2.35 ± 0.38 nmol/mol for three closely related species important in bioherm accumulationHalimeda copiosa, Halimeda hederacea, andHalimeda opuntia. Mn/Ca ratios, with means from 89–239 nmol/mol for these four species, showed both intra-and inter-specific variability. Sr/Ca ratios (10.9 ± O.1 mmol/mol) and Mg/Ca ratios (1.35 ± 0.26 mmol/mol) were similar for all samples. HoloceneHalimeda aragonite samples from cores of two bioherms in the northern GBR seemed well preserved on the basis of mineralogy and Sr/Ca and Mg/Ca ratios similar to those in modernHalimeda aragonite. Cd/Ca ratios (overall mean 0.96 ± 0.15 nmol/mol) were lower than those measured in the modernHalimeda from the central GBR location. However, Mn/Ca ratios in both cores were substantially higher than in modernHalimeda aragonite. While it may be possible to extract paleoceanographic information fromHalimeda aragonite, substantial care is needed to evaluate and avoid the effects of post-depositional alteration.     

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.     

Phylogenetic Diversity and Community Structure of the Symbionts Associated with the Coralline Sponge Astrosclera willeyana of the Great Barrier Reef

The coralline sponge Astrosclera willeyana, considered to be a living representative of the reef-building stromatoporoids of the Mesozoic and the Paleozoic periods, occurs widely throughout the Indo-Pacific oceans. We aimed to examine, for the first time, the phylogenetic diversity of the microbial symbionts associated with A. willeyana using molecular methods and to investigate the spatial variability in the sponge-derived microbial communities of A. willeyana from diverse sites along the Great Barrier Reef (GBR). Both denaturing gradient gel electrophoresis (DGGE) analyses of 12 Astrosclera specimens and sequencing of a 16S rRNA gene clone library, constructed using a specimen of A. willeyana from the Yonge Reef (380 clones), revealed the presence of a complex microbial community with high diversity. An assessment of the 16S rRNA gene sequences to the particular phylogenetic groups showed domination of the Chloroflexi (42 %), followed by the Gammaproteobacteria (14 %), Actinobacteria (11 %), Acidobacteria (8 %), and the Deferribacteres (7 %). Of the microbes that were identified, a further 15 % belonged to the Deltaproteobacteria, Alphaproteobacteria, and Nitrospirae genera. The minor phylogenetic groups Gemmatimonadetes, Spirochaetes, Cyanobacteria, Poribacteria, and the Archaea composed 3 % of the community. Over 94 % of the sequences obtained from A. willeyana grouped together with other sponge- or coral-derived sequences, and of these, 72 % formed, with nearest relatives, 46 sponge-specific or sponge–coral clusters, highlighting the uniqueness of the microbial consortia in sponges. The DGGE results showed clear divisions according to the geographical origin of the samples, indicating closer relationships between the microbial communities with respect to their geographic origin (northern vs. southern GBR).     

Currents and flusing of Britomart reef lagoon,Great Barrier Reef

Currents, sea levels and weather were measured for a 60 d period at a number of sites in and near Britomart reef, Great Barrier Reef. The tidal currents were primarily semi-diurnal in character. The lowfrequency currents were due to a simple balance, in the longshore direction, between the wind stress and the bottom frictional stress, and, in the cross-shelf direction, between the bottom frictional stress and the pressure gradient generated by the passage of wind-driven continental shelf waves. The bottom friction coefficient, for the nonlinear drag law, is estimated to be of the order of 0.02. By contrast, the currents over the surrounding continental shelf are primarily controlled by continental shelf wave dynamics and are not dominated by friction. It thus appears that the water bodies in, respectively, the reef matrix and the Lagoon of the Great Barrier Reef are relatively uncoupled. Tidal and low-frequency currents contributed roughly equally to the flushing of Britomart reef lagoon with an estimated flushing time of the order of 4 d.