Coastal climate of northwest Australia and comparisons with the Great Barrier Reef: 1960 to 1992

 Significant coral reef ecosystems occur along the northwest (NW) coast of Australia in an oceanographic setting somewhat similar to that of the Great Barrier Reef off the northeast (NE) Australian coast. Seasonal and inter-annual variations of several surface climate variables are described for the NW coastal region of Australia from 10^°–30^°S over the period 1960 to 1992. Average climatic conditions in this region are compared with those for similar latitudes on the Great Barrier Reef. On average, sea surface temperatures (SSTs) along the NW Australian coast are warmer than at similar latitudes along the NE coast north of ∼20^°S and cooler than the NE coast at higher latitudes. The annual range of SSTs along the NW coast is lower than found along the NE coast. There is also lower average cloud amount (and greater incoming solar radiation) along the NW coast compared with the NE coast. Corals reefs off the NW Australian coast are less likely to be influenced by freshwater and associated terrestrial impacts than nearshore reefs of the GBR. Although the latitudinal distribution of tropical cyclone activity is similar along the NW and NE Australian coasts, the total number of tropical cyclones and tropical cyclone days is substantially higher on the NW coast compared with the NE coast. Accepted: 22 June 1998     

Large-scale bleaching of corals on the Great Barrier Reef

 The Great Barrier Reef (GBR) experienced its most intensive and extensive coral bleaching event on record in early 1998. Mild bleaching commenced in late January and intensified by late February/early March 1998. Broad-scale aerial surveys conducted of 654 reefs (∼23% of reefs on the GBR) in March and April 1998, showed that 87% of inshore reefs were bleached at least to some extent (>1% of coral cover) compared to 28% of offshore (mid- and outer-shelf) reefs. Of inshore reefs 67% had high levels of bleaching (>10% of coral) and 25% of inshore reefs had extreme levels of bleaching (>60% of coral). Fewer offshore reefs (14%) showed high levels of bleaching while none showed extreme levels of bleaching. Ground-truth surveys of 23 reefs, which experienced bleaching in intensities ranging from none to extreme, showed that the aerial survey data are likely to be underestimates of the true extent and intensity of bleaching on the GBR. The primary cause of this bleaching event is likely to be elevated sea temperature and solar radiation, exacerbated by lowered salinity on inshore and some offshore reefs in the central GBR. Accepted: 30 July 1998     

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.     

Holocene evolution of the granite based Lizard Island and MacGillivray Reef systems, Northern Great Barrier Reef

Radiocarbon dating of seven drill cores from both the windward Lizard Island fringing reef and the windward and leeward margins of MacGillivray platform reef, Northern Great Barrier Reef Province, reveal the Holocene evolution of these two mid shelf coral reefs. The windward margin at Lizard Island started growing approximately 6,700 calendar years before present (cal yr BP) directly on an assumed granite basement and approached present day sea level approximately 4,000 cal yr BP. Growth of the windward margin at MacGillivray Reef was initiated by 7,600 cal yr BP and approached present day sea level by approximately 5,600 cal yr BP. The leeward margin at MacGillivray was initiated by 8,200 cal yr BP also directly on an assumed granite basement, but only approached sea level relatively recently, between 260 and 80 cal yr BP. None of the cores penetrated the Holocene-Pleistocene unconformity. The absence of Pleistocene reefal deposits, at 15 m depth in the cores from MacGillivray Reef, raises the possibility that the shelf in this region has subsided relative to modern day sea level by at least 15 m since the last interglacial [125,000 years ago (ka)].     

Microbiological assessment of a disease outbreak on corals from Magnetic Island (Great Barrier Reef, Australia)

Unusual disease lesions were observed in Montipora corals on the fringing reef of Magnetic Island (Great Barrier Reef, Australia) following a period of high water temperature in early January 2002. Tissue death in Montipora spp. appeared as a black layer that spread rapidly across the colony surface, though this appeared as the final phase of disease progression (with three previous disease phases now identified, S. Anthony, unpublished). Culture and molecular-based microbial analysis of this layer did not identify a likely microbial pathogen. Despite this, DNA sequencing of microbial 16S rDNA indicated a shift in the bacterial population associated with affected coral tissue. A clone library of the healthy coral sample predominantly contained sequences within the -Proteobacteria. A disease coral sample representing the margin of the black lesion and healthy coral tissue was dominated by sequences, which demonstrated low sequence identity to a range of -Proteobacteria, -Proteobacteria and cyanobacteria. The microbes identified in the diseased Montipora spp. samples are likely to be opportunistic rather than the causative agent of the observed lesion. Studies are in progress to further characterise the ecology of this disease and describe the potential microbial pathogen(s).     

Symbiodinium (Dinophyceae) community patterns in invertebrate hosts from inshore marginal reefs of the southern Great Barrier Reef,Australia

The broad range in physiological variation displayed by Symbiodinium spp. has proven imperative during periods of environmental change and contribute to the survival of their coral host. Characterizing how host and Symbiodinium community assemblages differ across environmentally distinct habitats provides useful information to predict how corals will respond to major environmental change. Despite the extensive characterizations of Symbiodinium diversity found amongst reef cnidarians on the Great Barrier Reef (GBR) substantial biogeographic gaps exist, especially across inshore habitats. Here, we investigate Symbiodinium community patterns in invertebrates from inshore and mid‐shelf reefs on the southern GBR, Australia. Dominant Symbiodinium types were characterized using denaturing gradient gel electrophoresis fingerprinting and sequencing of the ITS2 region of the ribosomal DNA. Twenty one genetically distinct Symbiodinium types including four novel types were identified from 321 reef‐invertebrate samples comprising three sub‐generic clades (A, C, and D). A range of host genera harbored C22a, which is normally rare or absent from inshore or low latitude reefs in the GBR. Multivariate analysis showed that host identity and sea surface temperature best explained the variation in symbiont communities across sites. Patterns of changes in Symbiodinium community assemblage over small geographic distances (100s of kilometers or less) indicate the likelihood that shifts in Symbiodinium distributions and associated host populations, may occur in response to future climate change impacting the GBR.     

Declining coral calcification in massive Porites in two nearshore regions of the northern Great Barrier Reef

Temporal and spatial variation in the growth parameters skeletal density, linear extension and calcification rate in massive Porites from two nearshore regions of the northern Great Barrier Reef (GBR) were examined over a 16‐year study period. Calcification rates in massive Porites have declined by approximately 21% in two regions on the GBR ～450 km apart. This is a function primarily of a decrease in linear extension (～16%) with a smaller decline in skeletal density (～6%) and contrasts with previous studies on the environmental controls on growth of massive Porites on the GBR. Changes in the growth parameters were linear over time. Averaged across colonies, skeletal density declined over time from 1.32 g cm^?3 (SE = 0.017) in 1988 to 1.25 g cm^?3 (0.013) in 2003, equivalent to 0.36% yr^?1 (0.13). Annual extension declined from 1.52 cm yr^?1 (0.035) to 1.28 cm yr^?1 (0.026), equivalent to 1.02% yr^?1 (0.39). Calcification rates (the product of skeletal density and annual extension) declined from 1.96 g cm^?2 yr^?1 (0.049) to 1.59 g cm^?2 yr^?1 (0.041), equivalent to 1.29% yr^?1 (0.30). Mean annual seawater temperatures had no effect on skeletal density, but a modal effect on annual extension and calcification with maxima at ～26.7 °C. There were minor differences in the growth parameters between regions. A decline in coral calcification of this magnitude with increasing seawater temperatures is unprecedented in recent centuries based on analysis of growth records from long cores of massive Porites. We discuss the decline in calcification within the context of known environmental controls on coral growth. Although our findings are consistent with studies of the synergistic effect of elevated seawater temperatures and pCO₂ on coral calcification, we conclude that further data on seawater chemistry of the GBR are required to better understand the links between environmental change and effects on coral growth.     

Spatio-temporal variation in coral recruitment at different scales on Heron Reef, southern Great Barrier Reef

 Recruitment of scleractinian corals on settlement plates at Heron Island, Great Barrier Reef, was examined over four years (September 1991–September 1995) to quantify spatio-temporal patterns at different scales and to assess post settlement mortality. Recruitment was dominated by pocilloporid corals which accounted for 80.1% of the 8627 spat counted, whereas non-isoporan acroporids represented only 16.4%. Poritids, faviids and isoporan acroporids rarely recruited to the plates (3.5%), despite their obvious abundance as adults on the reef. Recruitment patterns on the plates indicate strong space-time interactions as evidenced by patchy recruitment of both pocilloporid and acroporid spat. Interactions were found between space (on the scale of 10² m, i.e. sites within zones, and 10¹ m, i.e. racks within sites) and time (on the scale of years) for pocilloporids and between space (on the scale of 10³ m, i.e. zones, and 10² m) and time (on the scale of years) for acroporids. Post-recruitment mortality of acroporid spat in the period 3–10 months after their major spawning was dependent on their initial recruitment density, but pocilloporid mortality was either independent of initial recruitment density or, more likely, obscured by additional recruitment of pocilloporids to plates between late February and September. High rates of recruitment and growth by other sessile organisms, particularly bryozoans and oysters, appear to result in increased post-recruitment mortality and limit recruitment of scleractinian corals on settlement plates. The work reinforces an emerging picture that coral recruitment patterns are determined by mechanisms that manifest over a large range of spatial scales. Accepted: 1 September 1997     

A comparison of the 1998 and 2002 coral bleaching events on the Great Barrier Reef: spatial correlation,patterns, and predictions

Detailed mapping of coral bleaching events provides an opportunity to examine spatial patterns in bleaching over scales of 10 s to 1,000 s of km and the spatial correlation between sea surface temperature (SST) and bleaching. We present data for two large-scale (2,000 km) bleaching events on the Great Barrier Reef (GBR): one from 1998 and another from 2002, both mapped by aerial survey methods. We examined a wide range of satellite-derived SST variables to determine which one best correlated with the observed bleaching patterns. We found that the maximum SST occurring over any 3-day period (max3d) during the bleaching season predicted bleaching better than anomaly-based SST variables and that short averaging periods (3–6 days) predicted bleaching better than longer averaging periods. Short periods of high temperature are therefore highly stressful to corals and result in highly predictable bleaching patterns. Max3d SST predicted the presence/absence of bleaching with an accuracy of 73.2%. Large-scale (GBR-wide) spatial patterns of bleaching were similar between 1998 and 2002 with more inshore reefs bleached compared to offshore reefs. Spatial change in patterns of bleaching occurred at scales of ~10 s km, indicating that reefs bleach (or not) in spatial clusters, possibly due to local weather patterns, oceanographic conditions, or both. Approximately 42% of reefs bleached to some extent in 1998 with ~18% strongly bleached, while in 2002, ~54% of reefs bleached to some extent with ~18% strongly bleached. These statistics and the fact that nearly twice as many offshore reefs bleached in 2002 compared to 1998 (41 vs. 21%, respectively) makes the 2002 event the worst bleaching event on record for the GBR. Modeling of the relationship between bleaching and max3d SST indicates that a 1 °C increase would increase the bleaching occurrence of reefs from 50% (approximate occurrence in 1998 and 2002) to 82%, while a 2 °C increase would increase the occurrence to 97% and a 3 °C increase to 100%. These results suggest that coral reefs are profoundly sensitive to even modest increases in temperature and, in the absence of acclimatization/adaptation, are likely to suffer large declines under mid-range International Panel for Climate Change predictions by 2050.

Copepoda associated with the coral Gardineroseris planulata (Dana) on the Great Barrier Reef,northeastern Australia

Three new lichomolgid copepods associated with the scleractinian Gardineroseris planulata (Dana) are described: Sociellus torus, n. gen., n. sp., characterized by a 2-segmented endopod in leg 3 and the lack of an inner seta on the first segment of the endopod in legs 1–3; Odontomolgus pumilus, n. sp., of very small size and having a much elongated free segment in leg 5 of the female; and Paramolgus ampullaceus, n. sp., distinguished by the bottle-shaped genital segment of the female. In addition, the harpacticoid Alteuthellopsis corallina Humes, 1981, is reported from this coral. With the inclusion of 3 species of the poecilostomatoid genus Xarifia already described (Humes, 1985) there are now 7 species of copepods known to be associated with Gardineroseris planulata on the Great Barrier Reef.     

Dynamical seasonal prediction of summer sea surface temperatures in the Great Barrier Reef

Coral bleaching is a serious problem threatening the world coral reef systems, triggered by high sea surface temperatures (SST) which are becoming more prevalent as a result of global warming. Seasonal forecasts from coupled ocean–atmosphere models can be used to predict anomalous SST months in advance. In this study, we assess the ability of the Australian Bureau of Meteorology seasonal forecast model (POAMA) to forecast SST anomalies in the Great Barrier Reef, Australia, with particular focus on the major 1998 and 2002 bleaching events. Advance warning of potential bleaching events allows for the implementation of management strategies to minimise reef damage. This study represents the first attempt to apply a dynamical seasonal model to the problem of coral bleaching and predict SST over a reef system for up to 6 months lead-time, a potentially invaluable tool for reef managers. Communicated by Geology Editor Dr Bernhard Riegl     

Nemerteans of the Great Barrier Reef 1. Anopla Palaeonemertea

Two new palaeonemerteans, Carinoma patriciae sp. nov. , and Hubrechtella queenslandica sp. nov. , from the Great Barrier Reef province of Australia, are described and illustrated. The systematic relationships of these nemerteans are discussed and emended diagnoses are given for the genera Carinoma (Carinomidae) and Hubrechtella (Hubrechtidae).     

Enhanced particle-feeding capacity of corals on turbid reefs (Great Barrier Reef, Australia)

Reef corals occur across a wide range of habitats, from offshore clear waters to nearshore sediment-laden environments. This study tests the hypothesis that corals from turbid nearshore areas have greater capacity to utilise suspended sediment as a food source than conspecifics from less turbid and midshelf areas. The hypothesis was tested on two common and widespread coral species on the Great Barrier Reef (Pocillopora damicornis and Acropora millepora). The particle clearance rates of samples from more turbid reefs were two-fourfold those of conspecifics from less turbid and midshelf reefs. Rates of sediment ingestion were generally a linear function of sediment load indicating no significant saturation within the concentration range of 1–30 mg dry weight l⁻¹. Estimated assimilation efficiency of particulate ¹⁴C varied between 50 and 80%, and was maximised for midshelf A. millepora at the lowest sediment concentration, suggesting that heterotrophy is more efficient in oligotrophic habitats. Based on feeding-response curves, assimilation efficiencies, and published records of ambient particle concentrations, representatives of these species on turbid inshore reefs are 10–20 times more heterotrophic on suspended sediment than their conspecifics on less turbid and midshelf reefs. Accepted: 7 September 1999     

Bommies away! Logistics and early effects of repositioning 400 tonnes of displaced coral colonies following cyclone impacts on the Great Barrier Reef

For over 40 years, management of the Great Barrier Reef Marine Park (GBRMP) in Australia has focused on limiting human‐use impacts to facilitate natural resilience and recovery. Compounding acute disturbances and chronic stressors have resulted in degradation of coral reef habitats in many areas of the Marine Park. Given current trends and predictions of escalating climate‐driven disturbances, it is increasingly evident that effective management of the GBRMP requires adaptive and novel approaches to protect and restore coral reef health. Here, we provide an overview of the logistical requirements and early‐stage ecological benefits of repositioning 400 tonnes of moderately sized (1–3 m diameter) Porites spp. coral colonies (bommies) that were displaced by cyclone‐generated swells that impacted reefs in the Whitsunday Islands during March 2017. An ecological survey conducted 16 months after the bommie repositioning revealed that several genera of hard coral had settled onto the bommies and that a range of reef fish species were associating with the restored habitat. Early findings suggest that the repositioning of the displaced bommies has assisted in restoring reef habitat structure and settlement habitat for juvenile corals, while improving natural aesthetics, vessel access and tourist experiences at Manta Ray Bay.     

Identical digeneans in coral reef fishes from French Polynesia and the Great Barrier Reef (Australia) demonstrated by morphology and molecules

Three coral reef fish species, Zanclus cornutus, Chaetodon vagabundus and Naso lituratus, were collected in French Polynesia and on the Great Barrier Reef, Queensland. These fish species were each infected by one morphologically similar digenean species in both localities; Schistorchis zancli Hanson, 1953 was found in Zanclus cornutus, Preptetos laguncula Bray and Cribb, 1996 in Naso lituratus and Neohypocreadium dorsoporum Machida and Uchida, 1987 in Chaetodon vagabundus. In addition, on the Great Barrier Reef P. laguncula was also found in Naso unicornis and N. dorsoporum in Chaetodon ephippium and Chaetodon flavirostris. Morphometric differences between the species from the two sites were only slight. Sequences from the second internal transcribed spacer of the ribosomal DNA of each worm revealed total homology or negligible divergence between samples from hosts caught in French Polynesia and on the Great Barrier Reef. These results show that across more than 6000 km these digeneans are similar in morphology and genotype. Some species of fishes and molluscs are considered to have distributions that encompass the entire tropical Indo-West Pacific. These findings suggest that at least some of their parasites have similarly broad distributions.     

Importance of foraminifera for the formation and maintenance of a coral sand cay: Green Island, Australia

 CaCO₃ production by reef-building organisms on Green Island Reef in the Great Barrier Reef of Australia is estimated and compared with the contribution of benthic foraminifera to the sediment mass of the vegetated sand cay. Major constituents of the cay are benthic foraminifera (mainly Amphistegina lessonii, Baculogypsina sphaerulata, and Calcarina hispida), calcareous algae (Halimeda and coralline algae), hermatypic corals, and molluscs. Among these reef-building organisms, benthic foraminifera are the single most important contributor to the sediment mass of the island (ca. 30% of total sediments), although their production of CaCO₃ is smaller than other reef-building organisms. Water current measurements and sediment traps indicate that the velocity of the current around Green Island is suitable for transportation and deposition of foraminiferal tests. Abundant foraminifera presently live in association with algal turf on the shallow exposed reef flat, whose tests were accumulated by waves resulting in the formation and maintenance of the coral sand cay. Accepted: 30 June 1999     

Symbiodinium (Dinophyceae) diversity in reef‐invertebrates along an offshore to inshore reef gradient near Lizard Island,Great Barrier Reef

Despite extensive work on the genetic diversity of reef invertebrate‐dinoflagellate symbioses on the Great Barrier Reef (GBR; Australia), large information gaps exist from northern and inshore regions. Therefore, a broad survey was done comparing the community of inshore, mid‐shelf and outer reefs at the latitude of Lizard Island. Symbiodinium (Freudenthal) diversity was characterized using denaturing gradient gel electrophoresis fingerprinting and sequencing of the ITS2 region of the ribosomal DNA. Thirty‐nine distinct Symbiodinium types were identified from four subgeneric clades (B, C, D, and G). Several Symbiodinium types originally characterized from the Indian Ocean were discovered as well as eight novel types (C1kk, C1LL, C3nn, C26b, C161a, C162, C165, C166). Multivariate analyses on the Symbiodinium species diversity data showed a strong link with host identity, consistent with previous findings. Of the four environmental variables tested, mean austral winter sea surface temperature (SST) influenced Symbiodinium distribution across shelves most significantly. A similar result was found when the analysis was performed on Symbiodinium diversity data of genera with an open symbiont transmission mode separately with chl a and PAR explaining additional variation. This study underscores the importance of SST and water quality related variables as factors driving Symbiodinium distribution on cross‐shelf scales. Furthermore, this study expands our knowledge on Symbiodinium species diversity, ecological partitioning (including host‐specificity) and geographic ranges across the GBR. The accelerating rate of environmental change experienced by coral reef ecosystems emphasizes the need to comprehend the full complexity of cnidarian symbioses, including the biotic and abiotic factors that shape their current distributions.     

Trematodes of the Great Barrier Reef,Australia: emerging patterns of diversity and richness in coral reef fishes

The Great Barrier Reef holds the richest array of marine life found anywhere in Australia, including a diverse and fascinating parasite fauna. Members of one group, the trematodes, occur as sexually mature adult worms in almost all Great Barrier Reef bony fish species. Although the first reports of these parasites were made 100 years ago, the fauna has been studied systematically for only the last 25 years. When the fauna was last reviewed in 1994 there were 94 species known from the Great Barrier Reef and it was predicted that there might be 2,270 in total. There are now 326 species reported for the region, suggesting that we are in a much improved position to make an accurate prediction of true trematode richness. Here we review the current state of knowledge of the fauna and the ways in which our understanding of this fascinating group is changing. Our best estimate of the true richness is now a range, 1,100–1,800 species. However there remains considerable scope for even these figures to be incorrect given that fewer than one-third of the fish species of the region have been examined for trematodes. Our goal is a comprehensive characterisation of this fauna, and we outline what work needs to be done to achieve this and discuss whether this goal is practically achievable or philosophically justifiable.     

Biogeochemistry of inter-reef sediments on the northern and central Great Barrier Reef

The deposition and cycling of carbon and nitrogen in carbonate sediments located between coral reefs on the northern and central sections of the Great Barrier Reef were examined. Rates of mass sediment accumulation ranged from 1.9 kg m⁻² year⁻¹ (inshore reefs) to 2.1–4.9 kg m⁻² year⁻¹ (between mid-shelf reefs); sedimentation was minimal off outer-shelf reefs. Rates of total organic carbon decomposition ranged from 1.7 to 11.4 mol C m⁻² year⁻¹ and total nitrogen mineralization ranged from 77 to 438 mmol N m⁻² year⁻¹, declining significantly with distance from land. Sediment organic matter was highly reactive, with mineralization efficiencies ranging from 81 to 99% for organic carbon and 64–100% for nitrogen, with little C and N burial. There was no evidence of carbonate dissolution/precipitation in short-term incubation experiments. Rates of sulfate reduction (range 0–3.4 mmol S m⁻² day⁻¹) and methane release (range 0–12.8 μmol CH₄ m⁻² day⁻¹) were minor or modest pathways of carbon decomposition. Aerobic respiration, estimated by difference between total O₂ consumption and the sum of the other pathways, accounted for 55–98% of total carbon mineralization. Rates of ammonification ranged from 150 to 1,725 μmol NH₄ m⁻² day⁻¹, sufficient to support high rates of denitrification (range 30–2,235 μmol N₂ m⁻² day⁻¹). N₂O release was not detected and rates of NH₄ ⁺ and NO₂ ⁻ + NO₃ ⁻ efflux were low, indicating that most mineralized N was denitrified. The percentage of total N input removed via denitrification averaged ≈75% (range 28–100%) with little regenerated N available for primary producers. Inter-reef environments are therefore significant sites of energy and nutrient flow, especially in spatially complex reef matrices such as the Great Barrier Reef.