Phylogenetic diversity of bacteria associated with the marine sponge Rhopaloeides odorabile

Molecular techniques were employed to document the microbial diversity associated with the marine sponge Rhopaloeides odorabile. The phylogenetic affiliation of sponge-associated bacteria was assessed by 16S rRNA sequencing of cloned DNA fragments. Fluorescence in situ hybridization (FISH) was used to confirm the presence of the predominant groups indicated by 16S rDNA analysis. The community structure was extremely diverse with representatives of the Actinobacteria, low-G+C gram-positive bacteria, the beta- and gamma-subdivisions of the Proteobacteria, Cytophaga/Flavobacterium, green sulfur bacteria, green nonsulfur bacteria, planctomycetes, and other sequence types with no known close relatives. FISH probes revealed the spatial location of these bacteria within the sponge tissue, in some cases suggesting possible symbiotic functions. The high proportion of 16S rRNA sequences derived from novel actinomycetes is good evidence for the presence of an indigenous marine actinomycete assemblage in R. odorabile. High microbial diversity was inferred from low duplication of clones in a library with 70 representatives. Determining the phylogenetic affiliation of sponge-associated microorganisms by 16S rRNA analysis facilitated the rational selection of culture media and isolation conditions to target specific groups of well-represented bacteria for laboratory culture. Novel media incorporating sponge extracts were used to isolate bacteria not previously recovered from this sponge.     

Microbial symbionts of the Australian Great Barrier Reef sponge, Candidaspongia flabellata

Microbial symbionts of the newly described rare, biochemically active Dictyoceratid sponge, Candidaspongia flabellata (Very White Fan) found in the Australian Great Barrier Reef, are being studied in detail. The chemistry of this sponge species is distinctive, and includes a previously undescribed compound, fanolide as well as homosesterterpene and bishomoscalarane secondary metabolites (Bergquist et al., 1999). Current research is focused on assessing the diversity of the microbial community associated with this sponge. The entire culturable community of this sponge has been studied in detail. A total of 228 bacteria, 25 fungi, 3 actinomycetes and 9 cyanobacteria were isolated from 10 individuals of this sponge. Eight eubacteria (designated AB001–AB008), along with seven cyanobacteria were consistently found associated with C. flabellata and absent from the surrounding water column, suggesting that these bacteria have a specific association with the sponge. Partial 16S ribosomal RNA gene sequencing of these isolates was done for phylogenetic characterisation. Electron microscopy was also used to confirm the presence of many morphotypes of bacteria and indicated spatial arrangements of particular morphotypes.     

Patterns in the distribution of sponge populations across the central Great Barrier Reef

Coral reef sponge populations were surveyed at two spatial scales: different depths and different reef locations across the continental shelf of the central Great Barrier Reef. The surveys were conducted on the forereef slopes of 12 reefs from land-influenced, inner-shelf reefs to those in the oligotrophic waters of the Coral Sea. Few sponges occur in shallow waters and the largest populations are found between 10 and 30 m depth. Sponges are apparently excluded from shallow waters because of excessive turbulence and possibly by high levels of damaging light. Sponge biomass is highest on the innershelf reefs and decreases away from the coast, whereas abundance is generally higher on middle-shelf reefs. There are considerable overlaps in the species composition on middle-, outer-shelf and Coral Sea reefs, but those on inner-shelf reefs are significantly different. The nature and size of sponge populations reflect environmental conditions across the continental shelf. The larger inner-shelf populations probably reflect higher levels of organic and inorganic nutrients and reduced amounts of physical turbulence, whereas sponges on reefs further from shore may be able to resist greater turbulence but appear more sensitive to the effects of fine sediments. These latter populations are smaller, reflecting the reduced availability of organic matter, however, many of these sponges rely on cyanobacterial symbionts to augment nutrition in these clearer, more oligotrophic waters.Contribution no. 487 from the Australian Institute of Marine Science     

Specificity of bacterial symbionts in Mediterranean and Great Barrier Reef sponges

Bacteria were isolated from marine sponges from the Mediterranean and the Great Barrier Reef and characterized using numerical taxonomy techniques. A similar sponge-specific bacterial symbiont was found in 9 of 10 sponges examined from both geographic regions. This symbiont occurred in sponges of two classes and seven orders, and it probably has been associated with sponges over a long geological time scale. Another symbiont apparently specific to the spongeVerongia aerophoba was found. This sponge is yellow-orange, similar in color to the bacterial symbiont. These symbionts are two of a large mixed bacterial population present in many sponges.This paper constitutes No. V in the series Microbial Associations in Sponges.     

Sunscreens, oxidative stress and antioxidant functions in marine organisms of the Great Barrier Reef

An overview of the biochemical photophysiology of tropical, reef-building corals is presented with a discussion on the biosynthetic relationship between natural UV-absorbing sunscreens and certain antioxidant functions in marine organisms. Our studies reveal that marine organisms, including 'UV-extremophilic' bacteria, are a rich source of novel antioxidants having potential for the development of commercial and biomedical applications. Novel sunscreening agents derived from tropical marine organisms of the Great Barrier Reef are in development. New marine-derived antioxidants are being isolated for testing as chemopreventatives in a variety of oxidatively degenerative diseases.     

Sunscreens,oxidative stress and antioxidant functions in marine organisms of the Great Barrier Reef

Abstract

An overview of the biochemical photophysiology of tropical, reef-building corals is presented with a discussion on the biosynthetic relationship between natural UV-absorbing sunscreens and certain antioxidant functions in marine organisms. Our studies reveal that marine organisms, including ‘UV-extremophilic’ bacteria, are a rich source of novel antioxidants having potential for the development of commercial and biomedical applications. Novel sunscreening agents derived from tropical marine organisms of the Great Barrier Reef are in development. New marine-derived antioxidants are being isolated for testing as chemopreventatives in a variety of oxidatively degenerative diseases.     

Phylogenetic Diversity of Bacteria Associated with the Marine Sponge Rhopaloeides odorabile

Molecular techniques were employed to document the microbial diversity associated with the marine sponge Rhopaloeides odorabile. The phylogenetic affiliation of sponge-associated bacteria was assessed by 16S rRNA sequencing of cloned DNA fragments. Fluorescence in situ hybridization (FISH) was used to confirm the presence of the predominant groups indicated by 16S rDNA analysis. The community structure was extremely diverse with representatives of the Actinobacteria, low-G+C gram-positive bacteria, the β- and γ-subdivisions of the Proteobacteria, Cytophaga/Flavobacterium, green sulfur bacteria, green nonsulfur bacteria, planctomycetes, and other sequence types with no known close relatives. FISH probes revealed the spatial location of these bacteria within the sponge tissue, in some cases suggesting possible symbiotic functions. The high proportion of 16S rRNA sequences derived from novel actinomycetes is good evidence for the presence of an indigenous marine actinomycete assemblage in R. odorabile. High microbial diversity was inferred from low duplication of clones in a library with 70 representatives. Determining the phylogenetic affiliation of sponge-associated microorganisms by 16S rRNA analysis facilitated the rational selection of culture media and isolation conditions to target specific groups of well-represented bacteria for laboratory culture. Novel media incorporating sponge extracts were used to isolate bacteria not previously recovered from this sponge.     

Evidence for genetic structuring and limited dispersal ability in the Great Barrier Reef sponge Carteriospongia foliascens

Coral Reefs - Understanding connectivity patterns for coral reef organisms is important for their effective management. Despite sponges being an important component of the benthic fauna on the...     

Effect of substrate type on bacterial community composition in biofilms from the Great Barrier Reef

Natural and anthropogenic impacts such as terrestrial runoff, influence the water quality along the coast of the Great Barrier Reef (GBR) and may in turn affect coral reef communities. Associated bacterial biofilms respond rapidly to environmental conditions and are potential bioindicators for changes in water quality. As a prerequisite to study the effects of water quality on biofilm communities, appropriate biofilm substrates for deployment in the field must be developed and evaluated. This study investigates the effect of different settlement substrates (i.e. glass slides, ceramic tiles, coral skeletons and reef sediments) on bacterial biofilm communities grown in situ for 48 days at two locations in the Whitsunday Island Group (Central GBR) during two sampling times. Bacterial communities associated with the biofilms were analysed using terminal restriction fragment length polymorphism (T-RFLP) and clone library analyses of 16S rRNA genes. Findings revealed that substrate type had little influence on bacterial community composition. Of particular relevance, glass slides and coral skeletons exhibited very similar communities during both sampling times, suggesting the suitability of standardized glass slides for long-term biofilm indicator studies in tropical coral reef ecosystems.     

Modelling wind driven circulation One Tree Reef,Southern Great Barrier Reef

A vertically integrated numerical model of wind-driven circulation at One Tree Reef is presented. The model is the numerical model SURGE developed originally to study tropical cyclone surge. Current data collected in the reef lagoon and over the reef flats is used to test the model's applicability. The reef topography has been modelled explicitly, rather than using an assumed reef shape, with a grid spacing of 150 m. The model corresponds well to the measured current behaviour. The greatest drawback to use of the model is that, at low tide, currents reverse with depth due to lagoon enclosure and a depth integrated model cannot produce water velocity depth profiles. The model can be used to predict current behaviour in strong wind conditions, such as during a cyclone, and to estimate net flows into and out of the lagoon.     

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.     

Dynamics of phytoplankton in the Great Barrier Reef Lagoon

The characteristics of the phytoplankton crop in the centralregion of the Great Barrier Reef were analyzed through two annualcycles together with basic oceanographic parameters. Chlorophylla standing crop and primary production were size fractionatedinto nanoplankton and microplankton components. Community compositionwas determined using the Utermöhl settling technique andcommunity diversities estimated by the Shannon-Weaver equation.The data and analysis are the most comprehensive in existencefor the region, and the first detailed study since the 1928–29Great Barrier Reef expedition. A marked seasonal cycle was identified,contrary to most assumptions, closely associated with precipitationpatterns and nutrients introduced by land drainage. The regionwould rank as mesotrophic with some eutrophic areas in the innerreaches of the Lagoon. Oscillatoria spp. accounted for a largefraction of the majority of phytoplankton maxima and were inverselyrelated to diatom crop densities even under conditions favoringdiatom growth. Microplankton crop species diversities usuallydecreased during extended Oscillatoria blooms. The reduced diversitypersisted after the bloom suggesting that Oscillatoria spp.were the source of extracellular metabolites and/or decompositionproducts adversely influencing diatom microplankton.     

Marine actinomycetes related to the "Salinospora" group from the Great Barrier Reef sponge Pseudoceratina clavata

Ten strains identified as marine actinomycetes related to the "Salinospora" group previously reported only from marine sediments were isolated from the Great Barrier Reef marine sponge Pseudoceratina clavata. The relationship of the isolates to "Salinospora" was confirmed by phylogenetic analysis of 16S rRNA gene sequences. Colony morphology and pigmentation, occurrence and position of spores, and salinity requirements for growth were all consistent with this relationship. Genes homologous to beta-ketosynthase, an enzyme forming part of a polyketide synthesis complex, were retrieved from these isolates; these genes shared homology with other Type I ketosynthase genes, and phylogenetic comparison with amino acid sequences derived from database beta-ketosynthase genes was consistent with the close relationship of these isolates to the actinomycetes. Primers based on 16S rRNA gene sequences and designed for targeting amplification of members of the "Salinospora" group via polymerase chain reaction have been used to demonstrate occurrence of these actinomycetes within the sponge tissue. In vitro bioassays of extracts from the isolates for antibiotic activity demonstrated that these actinomycetes have the potential to inhibit other sponge symbionts in vivo, including both Gram-negative and Gram-positive bacteria.     

Bioerosion experiments at Lizard Island,Great Barrier Reef

The rates at which dead coral substrates are modified by bioerosional processes were determined by exposing recently killed corals for up to four years in a variety of reef environments at Lizard Island (northern Great Barrier Reef). Grazers were the major croding agents of these coral substrates and exhibited differences between sites that varied between sampling periods. Subtidal reef slopes and lagoon environments of water depths < 20 m were subjected to higher average rates of grazing erosion (0.30–1.96 kg/m²/y) than shallow depths less than 1 m (0.07–0.26 kg/m²/y). A deep site at 20 m experienced low average rates of grazing (0.08–0.29 kg/m²/y). Boring rates by worms (polychaetes and sipunculans), sponges and molluscs were relatively low and varied between sites, but increased with length of sampling period as larger borers succeeded the initial colonizing small polychaete worms. We hypothesize from these experiments that the extent of boring in reef substrates will be influenced by the interaction between the succession of the boring community and the rate at which the substrate is destroyed by grazing. We suggest that the level of grazing modifies the successional pattern of borers by removing the surface substrate and continually exposing bare substrate that can be colonized by early boring colonists. Thus, constant high levels of grazing may maintain the boring community at an early successional stage and prevent the development of a mature boring community. In order to establish large borer populations, reef substrates must be protected from extensive grazing bioerosion. This interaction of grazing and boring has important implications for the way dead coral is preserved in different reef environments.     

Coral community responses to declining water quality: Whitsunday Islands,Great Barrier Reef,Australia

A five-year period (2002–2006) of below-median rainfall followed by a six-year period (2007–2012) of above-median rainfall and seasonal flooding allowed a natural experiment into the effects of runoff on the water quality and subsequent coral community responses in the Whitsunday Islands, Great Barrier Reef (Australia). Satellite-derived water quality estimates of total suspended solids (TSS) and chlorophyll-a (Chl) concentration showed marked seasonal variability that was exaggerated during years with high river discharge. During above-median rainfall years, Chl was aseasonally high for a period of 3 months during the wet season (February–April), while TSS was elevated for four months, extending into the dry season (March–June). Coinciding with these extremes in water quality was a reduction in the abundance and shift in the community composition, of juvenile corals. The incidence of coral disease was at a maximum during the transition from years of below-median to years of above-median river discharge. In contrast to juvenile corals, the cover of larger corals remained stable, although the composition of communities varied along environmental gradients. In combination, these results suggest opportunistic recruitment of corals during periods of relatively low environmental stress with selection for more tolerant species occurring during periods of environmental extremes.     

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.