Patterns and rates of erosion in dead Porites across the Great Barrier Reef (Australia) after 2 years and 4 years of exposure

Rates and agents of erosion were investigated experimentally at six sites located along a cross shelf transect from the northern Queensland coast out into the Coral Sea. Rates of internal and external erosion of coral blocks, and accretion by coralline algae were measured after 2 years and 4 years of exposure. Blocks were cut from live colonies of Porites sp., which were collected from the outer barrier reef in north Queensland. They were then washed, dried, measured, weighed and attached to grids that were firmly attached to dead coral substrate at depths of 7–10 m. Significant differences in all three parameters were found within and among sites, and rates increased with increasing duration of exposure. Inshore sites were characterized by low rates of external erosion compared to offshore sites. Agents responsible for internal erosion differed among sites, with boring sponges being most abundant on the two inshore reefs, and molluscs most abundant at the offshore sites. Deposit-feeding polychaetes were more abundant at the two inshore sites, while filter and surface deposit feeders were more common at the offshore sites. Net erosion rates varied among sites (1.090±0.499 to 7.846±3.218 kg m²), and the relative importance of the components of erosion changed markedly along the cross-shelf transect.     

Incidence and severity of injuries among juvenile crown-of-thorns starfish on Australia’s Great Barrier Reef

Coral Reefs - Outbreaks of crown-of-thorns starfish (Acanthaster spp.) represent a major threat to coral reef ecosystems throughout the Indo-Pacific, and there is significant interest in whether...     

Effects of different disturbance types on butterflyfish communities of Australia’s Great Barrier Reef

The effects of disturbances on coral reef fishes have been extensively documented but most studies have relied on opportunistic sampling following single events. Few studies have the spatial and temporal extent to directly compare the effects of multiple disturbances over a large geographic scale. Here, benthic communities and butterflyfishes on 47 reefs of the Great Barrier Reef were surveyed annually to examine their responses to physical disturbances (cyclones and storms) and/or biological disturbances (bleaching, outbreaks of crown-of-thorns starfish and white syndrome disease). The effects on benthic and butterflyfish communities varied among reefs depending on the structure and geographical setting of each community, on the size and type of disturbance, and on the disturbance history of that reef. There was considerable variability in the response of butterflyfishes to different disturbances: physical disturbances (occurring with or without biological disturbances) produced substantial declines in abundance, whilst biological disturbances occurring on their own did not. Butterflyfishes with the narrowest feeding preferences, such as obligate corallivores, were always the species most affected. The response of generalist feeders varied with the extent of damage. Wholesale changes to the butterflyfish community were only recorded where structural complexity of reefs was drastically reduced. The observed effects of disturbances on butterflyfishes coupled with predictions of increased frequency and intensity of disturbances sound a dire warning for the future of butterflyfish communities in particular and reef fish communities in general.     

Coral Reefs on the Edge? Carbon Chemistry on Inshore Reefs of the Great Barrier Reef

While increasing atmospheric carbon dioxide (CO₂) concentration alters global water chemistry (Ocean Acidification; OA), the degree of changes vary on local and regional spatial scales. Inshore fringing coral reefs of the Great Barrier Reef (GBR) are subjected to a variety of local pressures, and some sites may already be marginal habitats for corals. The spatial and temporal variation in directly measured parameters: Total Alkalinity (TA) and dissolved inorganic carbon (DIC) concentration, and derived parameters: partial pressure of CO₂ (pCO₂); pH and aragonite saturation state (Ω_ar) were measured at 14 inshore reefs over a two year period in the GBR region. Total Alkalinity varied between 2069 and 2364 µmol kg⁻¹ and DIC concentrations ranged from 1846 to 2099 µmol kg⁻¹. This resulted in pCO₂ concentrations from 340 to 554 µatm, with higher values during the wet seasons and pCO₂ on inshore reefs distinctly above atmospheric values. However, due to temperature effects, Ω_ar was not further reduced in the wet season. Aragonite saturation on inshore reefs was consistently lower and pCO₂ higher than on GBR reefs further offshore. Thermodynamic effects contribute to this, and anthropogenic runoff may also contribute by altering productivity (P), respiration (R) and P/R ratios. Compared to surveys 18 and 30 years ago, pCO₂ on GBR mid- and outer-shelf reefs has risen at the same rate as atmospheric values (∼1.7 µatm yr⁻¹) over 30 years. By contrast, values on inshore reefs have increased at 2.5 to 3 times higher rates. Thus, pCO₂ levels on inshore reefs have disproportionately increased compared to atmospheric levels. Our study suggests that inshore GBR reefs are more vulnerable to OA and have less buffering capacity compared to offshore reefs. This may be caused by anthropogenically induced trophic changes in the water column and benthos of inshore reefs subjected to land runoff.     

Assessing loss of coral cover on Australia’s Great Barrier Reef over two decades, with implications for longer-term trends

While coral reefs in many parts of the world are in decline as a direct consequence of human pressures, Australia’s Great Barrier Reef (GBR) is unusual in that direct human pressures are low and the entire system of ~2,900 reefs has been managed as a marine park since the 1980s. In spite of these advantages, standard annual surveys of a large number of reefs showed that from 1986 to 2004, average live coral cover across the GBR declined from 28 to 22%. This overall decline was mainly due to large losses in six (21%) of 29 subregions. Declines in live coral cover on reefs in two inshore subregions coincided with thermal bleaching in 1998, while declines in four mid-self subregions were due to outbreaks of predatory starfish. Otherwise, living coral cover increased in one subregion (3%) and 22 subregions (76%) showed no substantial change. Reefs in the great majority of subregions showed cycles of decline and recovery over the survey period, but with little synchrony among subregions. Two previous studies examined long-term changes in live coral cover on GBR reefs using meta-analyses including historical data from before the mid-1980s. Both found greater rates of loss of coral and recorded a marked decrease in living coral cover on the GBR in 1986, coinciding exactly with the start of large-scale monitoring. We argue that much of the apparent long-term decrease results from combining data from selective, sparse, small-scale studies before 1986 with data from both small-scale studies and large-scale monitoring surveys after that date. The GBR has clearly been changed by human activities and live coral cover has declined overall, but losses of coral in the past 40–50 years have probably been overestimated.     

Holocene sea level instability in the southern Great Barrier Reef,Australia: high-precision U–Th dating of fossil microatolls

Three emergent subfossil reef flats from the inshore Keppel Islands, Great Barrier Reef (GBR), Australia, were used to reconstruct relative sea level (RSL). Forty-two high-precision uranium–thorium (U–Th) dates obtained from coral microatolls and coral colonies (2σ age errors from ±8 to 37 yr) in conjunction with elevation surveys provide evidence in support of a nonlinear RSL regression throughout the Holocene. RSL was as least 0.75 m above present from ~6500 to 5500 yr before present (yr BP; where “present” is 1950). Following this highstand, two sites indicated a coeval lowering of RSL of at least 0.4 m from 5500 to 5300 yr BP which was maintained for ~200 yr. After the lowstand, RSL returned to higher levels before a 2000-yr hiatus in reef flat corals after 4600 yr BP at all three sites. A second possible RSL lowering event of ~0.3 m from ~2800 to 1600 yr BP was detected before RSL stabilised ~0.2 m above present levels by 900 yr BP. While the mechanism of the RSL instability is still uncertain, the alignment with previously reported RSL oscillations, rapid global climate changes and mid-Holocene reef “turn-off” on the GBR are discussed.

     

Temporal consistency in background mortality of four dominant coral taxa along Australia’s Great Barrier Reef

Studies on the population and community dynamics of scleractinian corals typically focus on catastrophic mortality associated with acute disturbances (e.g., coral bleaching and outbreaks of crown-of-thorns starfish), though corals are subject to high levels of background mortality and injuries caused by routine and chronic processes. This study quantified prevalence (proportion of colonies with injuries) and severity (areal extent of injuries on individual colonies) of background mortality and injuries for four common coral taxa (massive Porites, encrusting Montipora, Acropora hyacinthus and branching Pocillopora) on the Great Barrier Reef, Australia. Sampling was conducted over three consecutive years during which there were no major acute disturbances. A total of 2276 adult colonies were surveyed across 27 sites, within nine reefs and three distinct latitudinal sectors. The prevalence of injuries was very high (>83%) across all four taxa, but highest for Porites (91%) and Montipora (85%). For these taxa (Montipora and Pocillopora), there was also significant temporal and spatial variation in prevalence of partial mortality. The severity of injuries ranged from 3% to more than 80% and varied among coral taxa, but was fairly constant spatially and temporally. This shows that some injuries have considerable longevity and that corals may invest relatively little in regenerating tissue over sites of previous injuries. Inter-colony variation in the severity of injury also had no apparent effect on the realized growth of individual colonies, suggesting that energy diverted to regeneration has a limited bearing on overall energetic allocation, or impacts on other life-history processes (e.g., reproduction) rather than growth. Establishing background levels of injury and regeneration is important for understanding energy investment and life-history consequences for reef-building corals as well as for predicting susceptibility to, and capacity to recover from, acute disturbances.     

Stability of coral–endosymbiont associations during and after a thermal stress event in the southern Great Barrier Reef

Shifts in the community of symbiotic dinoflagellates to those that are better suited to the prevailing environmental condition may provide reef-building corals with a rapid mechanism by which to adapt to changes in the environment. In this study, the dominant Symbiodinium in 10 coral species in the southern Great Barrier Reef was monitored over a 1-year period in 2002 that coincided with a thermal stress event. Molecular genetic profiling of Symbiodinium communities using single strand conformational polymorphism of the large subunit rDNA and denaturing gradient gel electrophoresis of the internal transcribed spacer 2 region did not detect any changes in the communities during and after this thermal-stress event. Coral colonies of seven species bleached but recovered with their original symbionts. This study suggests that the shuffling or switching of symbionts in response to thermal stress may be restricted to certain coral species and is probably not a universal feature of the coral–symbiont relationship. Communicated by Biology Editor Dr. Clay Cook     

Changes in coral assemblages during an outbreak of Acanthaster planci at Lizard Island, northern Great Barrier Reef (1995–1999)

Population outbreaks of crown-of-thorns starfish (Acanthaster planci L.) represent one of the most significant biological disturbances on tropical coral reefs and have the potential to devastate coral communities, thereby altering the biological and physical structure of reef habitats. This study reports on changes in area cover, species diversity and taxonomic composition of corals during an outbreak of A. planci at Lizard Island, in the northern Great Barrier Reef, Australia. Mean coral cover declined by 28.8% across ten locations studied. However, densities of A. planci, and their effects on local coral assemblages, were very patchy. Declines in coral cover were mostly due to the selective removal of certain coral taxa (mainly Acropora and Pocilloporidae corals); such that the greatest coral loss occurred at locations with highest initial cover of preferred coral prey. Most notably, coral assemblages in back-reef locations were transformed from topographically complex staghorn Acropora-dominated habitats, to relatively depauperate assemblages dominated by alcyonacean soft corals. Although coral loss was greatest among formerly dominant taxa (especially Acropora), effects were sufficiently widespread across different coral taxa, such that overall coral diversity tended to decline. Clearly, moderate outbreaks of A. planci have the potential to greatly alter community structure of coral communities even if they do not devastate live corals. Recovery in this instance is expected to be very rapid given that all coral taxa persisted, and effects were greatest among fast growing corals.     

Effect of bêche-de-mer fishing on densities and size structure of Holothuria nobilis (Echinodermata: Holothuroidea) populations on the Great Barrier Reef

Decreasing catch rates for Holothuria nobilis (black teatfish) on the Great Barrier Reef (GBR) prompted management agencies to close the fishery for this species in October 1999. At the same time, we surveyed densities and size structure of H. nobilis populations in the main area fished on the GBR. Densities of H. nobilis on four reefs protected from fishing (approximately 20 ind. ha^-1) were about four times higher than those on 16 reefs open to fishing (approximately 5 ind. ha^-1). Each of four other reefs had been divided into an area protected from fishing and an open area. On the largest of these reefs (ca. 28 km long), densities of H. nobilis were nearly five times higher in the protected area compared to the area open to fishing. On three smaller reefs (<11 km long), however, densities were not significantly different between the open and protected area, and were similar to that on reefs completely open to fishing. The average weight of individuals was significantly reduced on fished reefs (1,763 g) compared to closed reefs (2,200 g). Thus, bêche-de-mer fishing led to a strong reduction of density and biomass of H. nobilis. The division of smaller reefs into open and closed zones appears not to provide sufficient protection, but reefs that are completely closed to fishing appear to provide some degree of protection. There were some indications that proximity to tourist attractions may enhance the effect of protection.     

Spatial pattern dynamics over 10 years in a conifer/broadleaved forest,northern Japan

The present study investigated stand dynamics during 10-year period in a conifer/broadleaved mixed forest in Hokkaido, northern Japan, focusing on spatially dependent recruitment, mortality and growth of two growth-form groups, deciduous broadleaved species and the dominant evergreen conifer Abies sachalinensis. The stand-level basal area was maintained over the 10-year period, while a compositional equilibrium at the individual species level was not confirmed. Univariate and bivariate spatial analyses revealed clustering of many of the constituent species. The absence of single-species patches suggested an ambiguous mosaic formed by co-occurrence of Abies and broadleaved trees. The trend towards an aggregated distribution of Abies and broadleaved trees was caused by spatially dependent recruitment rather than mortality. New recruits of broadleaved species were spatially associated with surviving broadleaved trees, while this was not the case for Abies. The degree of competitive effects on growth was not consistent over the 10-year period. Abies showed between-groups competition, but not within-group competition. In contrast, we found asymmetric competitions between the broadleaved trees. Our results suggest that Abies is not sufficiently competitively dominant to exclude broadleaved trees, and that the co-occurrence of the two growth-form groups might be maintained.     

Transglutaminases and their substrates in biology and human diseases: 50 years of growing

Transglutaminase is an enzyme able to play more than one enzymatic action, acting on a variety of different substrates. The growth of knowledge about the members of the enzyme transglutaminase’s family and its substrates since the last 50 years indicates a large interest and curiosity about this protein, whose function and structure was, but still is, an important object of research. On the other hand, the involvement in a number of human diseases together with the lack of knowledge about the biological functions played by some of the most studied members of this family, make this enzyme a fascinating field of study. The history of this enzyme and its substrates, whose cross-linking action was reported for the first time 50 years ago, suggests that an effort to increase knowledge and communication among researchers is required. To achieve this important result, 10 years ago an internet web page called worldwide happening around transglutaminase (WHAT) was created. Driven by these experiences, novel points-of-view to look at Transglutaminase and its substrates may be identified.     

Vegetation patterns and trajectories in disturbed landscapes, Great?Barrier?Island, northern New?Zealand

Fire has been a major driver of forest loss in New?Zealand. A conceptual model has been proposed in which positive feedbacks between vegetation, fire and soils can arrest regeneration of recurrently burned wet forest landscapes. We used vegetation data collected across three topographically similar landscapes ? Awana, Glenfern and Windy Hill ? on Great Barrier Island to (1) describe current vegetation composition and structure and predict future change in composition and (2) assess evidence for interactions between fire and soils slowing regeneration in these landscapes. Compositional data were analysed via classification and ordination, and we used transition matrix models to explore how vegetation composition may change in the future. The vegetation in the three landscapes spans repeatedly burned scrubland dominated by m?nuka (Leptospermum scoparium) and exotic fire-dependent woody species such as Hakea sericea, to intact mature forest. Scrubland vegetation tends to be found on north-facing upper slopes and ridges ? drier sites where fire has been more frequent and rendered soil conditions (e.g. organic matter and moisture) poor for plant growth. There is a slow reinvasion of forest species into the Leptospermum and Kunzea scrubland from gullies and other remnant patches, with wind-dispersed species preceding fleshy-fruited bird-dispersed ones. In the absence of fire in the next few decades the landscapes will continue to move back towards forest. More fires, however, will further degrade these landscapes by removing remaining fertile topsoils from ridges and slopes and by favouring exotic species adapted to recruit from seed and/or resprout vegetatively after fire.     

Theoretical and experimental studies on the inhibition potentials of aromatic oxaldehydes for the corrosion of mild steel in 0.1 M HCl

Experimental aspect of the inhibition of the corrosion of mild steel by oxaldehydes was carried out using gravimetric, gasometric and thermometric methods while the theoretical studies were carried out using quantum chemical principle and quantitative structure activity relation (QSAR) approaches. The results obtained indicated that the studied oxaldehydes are good inhibitors for the corrosion of mild steel in HCl solutions. The adsorption of the inhibitors on mild steel surface is spontaneous, exothermic and is consistent with the assumptions of Langmuir adsorption isotherm. Excellent correlations were found between the calculated quantum chemical parameters and experimental inhibition efficiencies of the studied compounds. Correlations between theoretical and experimental inhibition efficiencies (for the different Hamiltonians, namely, PM6, PM3, AM1, RM1 and MNDO) were very close to unity. Condensed Fukui function and condensed softness have been used to determine the sites for electrophilic and nucleophilic attacks on each of the inhibitors.     

Coral–macroalgal phase shifts or reef resilience: links with diversity and functional roles of herbivorous fishes on the Great Barrier Reef

Changes from coral to macroalgal dominance following disturbances to corals symbolize the global degradation of coral reefs. The development of effective conservation measures depends on understanding the causes of such phase shifts. The prevailing view that coral–macroalgal phase shifts commonly occur due to insufficient grazing by fishes is based on correlation with overfishing and inferences from models and small-scale experiments rather than on long-term quantitative field studies of fish communities at affected and resilient sites. Consequently, the specific characteristics of herbivorous fish communities that most promote reef resilience under natural conditions are not known, though this information is critical for identifying vulnerable ecosystems. In this study, 11 years of field surveys recorded the development of the most persistent coral–macroalgal phase shift (>7 years) yet observed on Australia’s Great Barrier Reef (GBR). This shift followed extensive coral mortality caused by thermal stress (coral bleaching) and damaging storms. Comparisons with two similar reefs that suffered similar disturbances but recovered relatively rapidly demonstrated that the phase shift occurred despite high abundances of one herbivore functional group (scraping/excavating parrotfishes: Labridae). However, the shift was strongly associated with low fish herbivore diversity and low abundances of algal browsers (predominantly Siganidae) and grazers/detritivores (Acanthuridae), suggesting that one or more of these factors underpin reef resilience and so deserve particular protection. Herbivorous fishes are not harvested on the GBR, and the phase shift was not enhanced by unusually high nutrient levels. This shows that unexploited populations of herbivorous fishes cannot ensure reef resilience even under benign conditions and suggests that reefs could lose resilience under relatively low fishing pressure. Predictions of more severe and widespread coral mortality due to global climate change emphasize the need for more effective identification and protection of ecosystem components that are critical for the prevention of coral reef phase shifts.     

Differences in demographic traits of four butterflyfish species between two reefs of the Great Barrier Reef separated by 1,200?km

Many species demonstrate variation in life history attributes in response to gradients in environmental conditions. For fishes, major drivers of life history variation are changes in temperature and food availability. This study examined large-scale variation in the demography of four species of butterflyfishes (Chaetodon citrinellus, Chaetodon lunulatus, Chaetodon melannotus, and Chaetodon trifascialis) between two locations on Australia’s Great Barrier Reef (Lizard Island and One Tree Island, separated by approximately 1,200 km). Variation in age-based demographic parameters was assessed using the re-parameterised von Bertalanffy growth function. All species displayed measurable differences in body size between locations, with individuals achieving a larger adult size at the higher latitude site (One Tree Island) for three of the four species examined. Resources and abundances of the study species were also measured, revealing some significant differences between locations. For example, for C. trifascialis, there was no difference in its preferred resource or in abundance between locations, yet it achieved a larger body size at the higher latitude location, suggesting a response to temperature. For some species, resources and abundances did vary between locations, limiting the ability to distinguish between a demographic response to temperature as opposed to a response to food or competition. Future studies of life histories and demographics at large spatial scales will need to consider the potentially confounding roles of temperature, resource usage and availability, and abundance/competition to disentangle the effects of these environmental variables.     

A new species of Numbakullidae Gu?u & Heard, 2002 (Tanaidacea,Peracarida, Crustacea) from?the?Great?Barrier Reef,Australia

A new species of Numbakulla Guţu & Heard, 2002 (Tanaidacea) is described from Heron Island (southern Great Barrier Reef, Queensland) collected during the Census of Coral Reefs Ecosystem (CReefs) program. The new species is the third member of the family and can be recognized by the combination of characters as: length/width ratio of the body, which is 6:7, pereonite 4 longer than the rest, the presence of eyes, a blunt rostrum, antenna article 2 elongated, cheliped carpus with row of inner setae, pereopod 6 carpus with spines, pleopod endopod with denticles.