Special Issue "Cross-shelf Variation in the Structure and Function of Coral Reef Assemblages"

A special issue of Diversity (ISSN 1424-2818). This special issue belongs to the section "Marine Diversity".

Deadline for manuscript submissions: closed (31 December 2018)

Special Issue Editors

Guest Editor
Dr. Andrew Hoey

James Cook University, Australia, Townsville, Australia
Website | E-Mail
Interests: herbivory; ecological resilience; parrotfishes; rabbitfishes; reef fish ecology; habitat structure; functional ecology; reef processes; ecology of macroalgae
Guest Editor
Prof. Morgan Pratchett

ARC Centre of Excellence for Coral Reef Studies, James Cook University, QLD 4811, Townsville, Australia
Website | E-Mail
Interests: butterflyfishes; coral biology; crown-of-thorns starfish; coral reef management; dietary and habitat specialisation; disturbance ecology; ecology of reef fishes
Guest Editor
Dr. Michael Emslie

Australian Institute of Marine Science, PMB 3, Townsville MC, QLD 4810
E-Mail
Interests: ecology of reef fishes; predatory fishes; butterflyfishes; spatial structure in reef fishes; disturbance ecology; coral reef management; efficacy of marine reserves; role of habitat complexity; recovery; behavioral ecology
Guest Editor
Dr. David Feary

School of Life Sciences, University of Nottingham, NG7 2RD, Nottingham, UK
Website | E-Mail
Interests: disturbance ecology; demography, behavior; reef fish ecology; marine protected areas; local management; population ecology

Special Issue Information

Dear Colleagues,

One of the most prevalent and striking gradients in the abundance of reef organisms and structure of reef assemblages occurs with increasing distance from the shore. In Australia’s Great Barrier Reef, for example, there are marked differences in environemntal conditions, the abundance and composition of key habitat-forming organisms, habitat structure, and abundance of functionally important taxa in inshore versus offshore reefs. The purpose of this Special Issue is to explore the generality of cross-shelf gradients among a diverse range of coral reef systems, and to better establish the relative contributions of environmental gradients, disturbances, and anthropogenic pressures in structuring cross-shelf patterns. We invite submissions that address any aspect of cross-shelf gradients in coral reef systems.

Dr. Andrew Hoey
Prof. Morgan Pratchett
Dr. Michael Emslie
Dr. David Feary
Guest Editors

Manuscript Submission Information

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Keywords

  • Cross-shelf gradient
  • Environmental conditions
  • Coral reef
  • Inshore vs offshore
  • Assemblage structure
  • Habitat structure
  • Benthic assemblages
  • Coral reef fishes
  • Ecosystem process

Published Papers (12 papers)

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Research

Open AccessArticle The Role of Maximum Shelf Depth versus Distance from Shore in Explaining a Diversity Gradient of Mushroom Corals (Fungiidae) off Jakarta
Diversity 2019, 11(3), 46; https://doi.org/10.3390/d11030046
Received: 30 January 2019 / Revised: 16 March 2019 / Accepted: 18 March 2019 / Published: 21 March 2019
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Abstract
Many coral reef systems are shelf-based and consist of reefs that are arranged in rows parallel to the coastline. They usually show an increase in species richness in the offshore direction, coinciding with decreasing terrigenous impact and a deeper seafloor. These two conditions [...] Read more.
Many coral reef systems are shelf-based and consist of reefs that are arranged in rows parallel to the coastline. They usually show an increase in species richness in the offshore direction, coinciding with decreasing terrigenous impact and a deeper seafloor. These two conditions usually concur, which makes it less easy to distinguish how each of them influences coral diversity separately. Since reefs off Jakarta (in the Thousand Islands archipelago) are arranged in an 80 km long string perpendicular to the coastline in south-to-north direction, with a maximum shelf depth halfway along (instead of at the end of) the string, this archipelago is very suitable for studies on inshore–offshore gradients. In the present study, mushroom corals (Fungiidae; n = 31) were used to examine diversity patterns on 38 reef sites along such a gradient, involving species richness over their entire depth range from reef flat to reef base (2–30 m) and separately at shallow depths (2–6 m). Total species diversity was highest in the central part of the archipelago, with unique species occurring in deep habitats. Diversity at shallow depths was only slightly higher here than at reefs located more nearshore and offshore, which both had less clear water. Therefore, shelf depth and distance from the mainland can be considered separate determinants of coral diversity off Jakarta. Full article
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Open AccessArticle Plasticity in Three-Dimensional Geometry of Branching Corals Along a Cross-Shelf Gradient
Diversity 2019, 11(3), 44; https://doi.org/10.3390/d11030044
Received: 31 January 2019 / Revised: 7 March 2019 / Accepted: 13 March 2019 / Published: 21 March 2019
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Abstract
Scleractinian corals often exhibit high levels of morphological plasticity, which is potentially important in enabling individual species to occupy benthic spaces across a wide range of environmental gradients. This study tested for differences in the three-dimensional (3D) geometry of three branching corals, Acropora [...] Read more.
Scleractinian corals often exhibit high levels of morphological plasticity, which is potentially important in enabling individual species to occupy benthic spaces across a wide range of environmental gradients. This study tested for differences in the three-dimensional (3D) geometry of three branching corals, Acropora nasuta, Pocillopora spp. and Stylophora pistillata among inner-, mid- and outer-shelf reefs in the central Great Barrier Reef, Australia. Important attributes of coral morphology (e.g., surface area to volume ratio) were expected to vary linearly across the shelf in accordance with marked gradients in environmental conditions, but instead, we detected non-linear trends in the colony structure of A. nasuta and Pocillopora spp. The surface area to volume ratio of both A. nasuta and Pocillopora spp. was highest at mid-shelf locations, (reflecting higher colony complexity) and was significantly lower at both inner-shelf and outer-shelf reefs. The branching structure of these corals was also far more tightly packed at inner-shelf and outer-shelf reefs, compared to mid-shelf reefs. Apparent declines in complexity and inter-branch spacing at inner and outer-shelf reefs (compared to conspecifics from mid-shelf reefs) may reflect changes driven by gradients of sedimentation and hydrodynamics. The generality and explanations of observed patterns warrant further investigation, which is very feasible using the 3D-photogrammetry techniques used in this study. Full article
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Open AccessArticle Cross-Shelf Variation in Coral Community Response to Disturbance on the Great Barrier Reef
Diversity 2019, 11(3), 38; https://doi.org/10.3390/d11030038
Received: 14 December 2018 / Revised: 27 February 2019 / Accepted: 1 March 2019 / Published: 6 March 2019
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Abstract
Changes in coral reef health and status are commonly reported using hard coral cover, however such changes may also lead to substantial shifts in coral community composition. Here we assess the extent to which coral communities departed from their pre-disturbance composition following disturbance [...] Read more.
Changes in coral reef health and status are commonly reported using hard coral cover, however such changes may also lead to substantial shifts in coral community composition. Here we assess the extent to which coral communities departed from their pre-disturbance composition following disturbance (disassembly), and reassembled during recovery (reassembly) along an environmental gradient across the continental shelf on Australia’s Great Barrier Reef. We show that for similar differences in coral cover, both disassembly and reassembly were greater on inshore reefs than mid- or outer-shelf reefs. This pattern was mostly explained by spatial variation in the pre-disturbance community composition, of which 28% was associated with chronic stressors related to water quality (e.g., light attenuation, concentrations of suspended sediments and chlorophyll). Tropical cyclones exacerbated the magnitude of community disassembly, but did not vary significantly among shelf positions. On the outer shelf, the main indicator taxa (tabulate Acropora) were mostly responsible for community dissimilarity, whereas contribution to dissimilarity was distributed across many taxa on the inner shelf. Our results highlight that community dynamics are not well captured by aggregated indices such as coral cover alone, and that the response of ecological communities to disturbance depends on their composition and exposure to chronic stressors. Full article
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Open AccessArticle The Distribution of Planktivorous Damselfishes (Pomacentridae) on the Great Barrier Reef and the Relative Influences of Habitat and Predation
Diversity 2019, 11(3), 33; https://doi.org/10.3390/d11030033
Received: 7 January 2019 / Revised: 22 February 2019 / Accepted: 25 February 2019 / Published: 28 February 2019
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Abstract
Planktivorous damselfishes (Pomacentridae) are diverse and abundant on the Great Barrier Reef (GBR), are important prey for commercially harvested coral trout (Plectropomus spp.) and their feeding mode plays a central role in transferring energy from the plankton to the reef. However, little [...] Read more.
Planktivorous damselfishes (Pomacentridae) are diverse and abundant on the Great Barrier Reef (GBR), are important prey for commercially harvested coral trout (Plectropomus spp.) and their feeding mode plays a central role in transferring energy from the plankton to the reef. However, little is known about their distribution patterns throughout the GBR and how those patterns are influenced by predators and habitat despite increasing pressures on both. Here we quantify the distribution and abundance of GBR planktivorous damselfishes, then examine the role of coral trout and habitat in shaping their assemblages. The assemblage structure of planktivorous damselfishes varied across the continental shelf, yet their total abundances varied sub-regionally, dependent on differences in coral habitat. Latitudinal patterns were relatively weak. Damselfish assemblages generally retained characteristics of their sub-regional setting over 20 years and assemblage degradation was only associated with major coral losses. Damselfish numbers were not negatively influenced by top-down control from coral trout. Instead, numbers of coral trout and damselfishes were both positively associated with coral habitat and each other. Our findings suggest that a complexity of factors and interactions shape reef fish assemblages and reinforce the fundamental importance of coral as the foundation of healthy reef communities. Full article
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Open AccessArticle Deep-Reef Fish Communities of the Great Barrier Reef Shelf-Break: Trophic Structure and Habitat Associations
Diversity 2019, 11(2), 26; https://doi.org/10.3390/d11020026
Received: 31 December 2018 / Revised: 11 February 2019 / Accepted: 11 February 2019 / Published: 20 February 2019
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Abstract
The ecology of habitats along the Great Barrier Reef (GBR) shelf-break has rarely been investigated. Thus, there is little understanding of how associated fishes interact with deeper environments. We examined relationships between deep-reef fish communities and benthic habitat structure. We sampled 48 sites [...] Read more.
The ecology of habitats along the Great Barrier Reef (GBR) shelf-break has rarely been investigated. Thus, there is little understanding of how associated fishes interact with deeper environments. We examined relationships between deep-reef fish communities and benthic habitat structure. We sampled 48 sites over a large depth gradient (54–260 m) in the central GBR using Baited Remote Underwater Video Stations and multibeam sonar. Fish community composition differed both among multiple shelf-break reefs and habitats within reefs. Epibenthic cover decreased with depth. Deep epibenthic cover included sponges, corals, and macro-algae, with macro-algae present to 194 m. Structural complexity decreased with depth, with more calcified reef, boulders, and bedrock in shallower depths. Deeper sites were flatter and more homogeneous with softer substratum. Habitats were variable within depth strata and were reflected in different fish assemblages among sites and among locations. Overall, fish trophic groups changed with depth and included generalist and benthic carnivores, piscivores, and planktivores while herbivores were rare below 50 m. While depth influenced where trophic groups occurred, site orientation and habitat morphology determined the composition of trophic groups within depths. Future conservation strategies will need to consider the vulnerability of taxa with narrow distributions and habitat requirements in unique shelf-break environments. Full article
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Open AccessArticle Cross-Shelf Differences in the Response of Herbivorous Fish Assemblages to Severe Environmental Disturbances
Diversity 2019, 11(2), 23; https://doi.org/10.3390/d11020023
Received: 2 January 2019 / Revised: 31 January 2019 / Accepted: 11 February 2019 / Published: 13 February 2019
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Abstract
Cross-shelf differences in coral reef benthic and fish assemblages are common, yet it is unknown whether these assemblages respond uniformly to environmental disturbances or whether local conditions result in differential responses of assemblages at different shelf positions. Here, we compare changes in the [...] Read more.
Cross-shelf differences in coral reef benthic and fish assemblages are common, yet it is unknown whether these assemblages respond uniformly to environmental disturbances or whether local conditions result in differential responses of assemblages at different shelf positions. Here, we compare changes in the taxonomic and functional composition, and associated traits, of herbivorous reef fish assemblages across a continental shelf, five years before and six months after two severe cyclones and a thermal bleaching event that resulted in substantial and widespread loss of live hard coral cover. Each shelf position maintained a distinct taxonomic assemblage of fishes after disturbances, but the assemblages shared fewer species among shelf positions. There was a substantial loss of species richness following disturbances within each shelf position. Total biomass of the herbivorous fish assemblage increased after disturbances on mid- and outer-shelf reefs, but not on inner-shelf reefs. Using trait-based analyses, we found there was a loss of trait richness at each shelf position, but trait specialisation and originality increased on inner-shelf reefs. This study highlights the pervasiveness of extreme environmental disturbances on ecological assemblages. Whilst distinct cross-shelf assemblages can remain following environmental disturbances, assemblages have reduced richness and are potentially more vulnerable to chronic localised stresses. Full article
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Open AccessArticle Spatial Patterns and Short-term Changes of Coral Assemblages Along a Cross-shelf Gradient in the Southwestern Lagoon of New Caledonia
Diversity 2019, 11(2), 21; https://doi.org/10.3390/d11020021
Received: 5 December 2018 / Revised: 29 January 2019 / Accepted: 1 February 2019 / Published: 5 February 2019
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Abstract
Coral reef assemblages generally form gradients of spatial structures which are governed by a variety of interacting physical and biological processes that vary in intensity, frequency, and spatial scale. Assessing the structure of contemporary reef assemblages may help to understand future changes and [...] Read more.
Coral reef assemblages generally form gradients of spatial structures which are governed by a variety of interacting physical and biological processes that vary in intensity, frequency, and spatial scale. Assessing the structure of contemporary reef assemblages may help to understand future changes and to identify appropriate conservation actions. The spatial distribution and interannual variability (from 2006 to 2008) of coral assemblages were investigated at 10 stations in the southwestern lagoon of New Caledonia, and the strength of the cross-shelf gradient was evaluated. Coral cover, generic richness, and abundance of adult and juvenile assemblages were highly variable within and among the three major reef habitats (fringing, mid-shelf, and barrier reefs). Abundance increased with distance from shore, whereas generic richness and cover were not correlated with shelf position. Assemblage composition was generally related to habitat, even though some mid-shelf and fringing reef assemblages resembled those observed on other habitats. A significant correlation between juvenile and adult distributions was recorded, suggesting that adult assemblages are partly controlled by the short-term history of recruitment patterns. The interannual variation of coral assemblages was far less pronounced, with significant changes only detected at some mid-shelf and barrier reefs, for a few genera characterised by high turn-over. Full article
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Open AccessArticle Hyperdiverse Macrofauna Communities Associated with a Common Sponge, Stylissa carteri, Shift across Ecological Gradients in the Central Red Sea
Diversity 2019, 11(2), 18; https://doi.org/10.3390/d11020018
Received: 31 December 2018 / Revised: 23 January 2019 / Accepted: 24 January 2019 / Published: 29 January 2019
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Abstract
Sponges act as important microhabitats in the marine environment and promote biodiversity by harboring a wide variety of macrofauna, but little is known about the magnitude and patterns of diversity of sponge-associated communities. This study uses DNA barcoding to examine the macrofaunal communities [...] Read more.
Sponges act as important microhabitats in the marine environment and promote biodiversity by harboring a wide variety of macrofauna, but little is known about the magnitude and patterns of diversity of sponge-associated communities. This study uses DNA barcoding to examine the macrofaunal communities associated with Stylissa carteri in the central Saudi Arabian Red Sea, an understudied ecosystem with high biodiversity and endemism. In total, 146 operational taxonomic units (OTUs) were distinguished from 938 successfully-sequenced macrofauna individuals from 99 sponges. A significant difference was found in the macrofaunal community composition of S. carteri along a cross-shelf gradient using OTU abundance (Bray–Curtis dissimilarity index), with more amphipods associated with offshore sponges and more brittle stars and fishes associated with inshore sponges. The abundance of S. carteri also showed a gradient, increasing with proximity to shore. However, no significant differences in macrofaunal community composition or total macrofauna abundance were observed between exposed and sheltered sides of the reefs and there was no significant change in total macrofauna abundance along the inshore–offshore gradient. As climate change and ocean acidification continue to impact coral reef ecosystems, understanding the ecology of sponges and their role as microhabitats may become more important for understanding their full ramifications for biodiversity. Full article
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Open AccessArticle Cross-shelf Heterogeneity of Coral Assemblages in Northwest Australia
Diversity 2019, 11(2), 15; https://doi.org/10.3390/d11020015
Received: 14 December 2018 / Revised: 14 January 2019 / Accepted: 17 January 2019 / Published: 22 January 2019
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Abstract
Understanding the spatial and temporal distribution of coral assemblages and the processes structuring those patterns is fundamental to managing reef assemblages. Cross-shelf marine systems exhibit pronounced and persistent gradients in environmental conditions; however, these gradients are not always reliable predictors of coral distribution [...] Read more.
Understanding the spatial and temporal distribution of coral assemblages and the processes structuring those patterns is fundamental to managing reef assemblages. Cross-shelf marine systems exhibit pronounced and persistent gradients in environmental conditions; however, these gradients are not always reliable predictors of coral distribution or the degree of stress that corals are experiencing. This study used information from government, industry and scientific datasets spanning 1980–2017, to explore temporal trends in coral cover in the geographically complex system of the Dampier Archipelago, northwest Australia. Coral composition at 15 sites surveyed in 2017 was also modelled against environmental and spatial variables (including turbidity, degree heat weeks, wave exposure, and distance to land/mainland/isobath) to assess their relative importance in structuring coral assemblages. High spatial and temporal heterogeneity was observed in coral cover and recovery trajectories, with reefs located an intermediate distance from the shore maintaining high cover over the past 20 years. The abundance of some prominent genera in 2017 (Acropora, Porites, and Turbinaria spp.) decreased with the distance from the mainland, suggesting that inshore processes play an important role in dictating the distribution of these genera. The atypical distributions of these key reef-building corals and spatial heterogeneity of historical recovery trajectories highlight the risks in making assumptions regarding cross-shelf patterns in geographically complex systems. Full article
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Open AccessArticle Diversity and Structure of Parrotfish Assemblages across the Northern Great Barrier Reef
Diversity 2019, 11(1), 14; https://doi.org/10.3390/d11010014
Received: 29 December 2018 / Revised: 16 January 2019 / Accepted: 17 January 2019 / Published: 18 January 2019
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Abstract
The structure and dynamics of coral reef environments vary across a range of spatial scales, with patterns of associated faunal assemblages often reflecting this variability. However, delineating drivers of biological variability in such complex environments has proved challenging. Here, we investigated the assemblage [...] Read more.
The structure and dynamics of coral reef environments vary across a range of spatial scales, with patterns of associated faunal assemblages often reflecting this variability. However, delineating drivers of biological variability in such complex environments has proved challenging. Here, we investigated the assemblage structure and diversity of parrotfishes—a common and ecologically important group—across 6° of latitude on the Northern Great Barrier Reef (GBR), Australia. Parrotfish abundance and biomass were determined from stereo-video surveys across 82 sites spanning 31 reefs and assessed against geographic, biophysical, and management-related factors in a multivariate framework to determine major drivers and associated scales of assemblage structure. Large cross-shelf variation in parrotfish assemblages pervaded along the entire Northern GBR, with distinct assemblages associated with sheltered and exposed reefs. Species abundances and diversity generally decreased with decreasing latitude. The gradient of explicit predator biomass associated with management zoning had no effect on parrotfish assemblage structure, but was positively correlated with parrotfish diversity. Our results highlight the ubiquitous presence of cross-shelf variation, where the greatest differences in parrotfish community composition existed between sheltered (inner and mid shelf) and exposed (outer shelf) reef systems. Prior attempts to explain linkages between parrotfishes and fine-scale biophysical factors have demonstrated parrotfishes as habitat generalists, but recent developments in nutritional ecology suggest that their cross-shelf variation on the GBR is likely reflective of benthic resource distribution and species-specific feeding modes. Full article
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Open AccessArticle Limited Cross-Shelf Variation in the Growth of Three Branching Corals on Australia’s Great Barrier Reef
Diversity 2018, 10(4), 122; https://doi.org/10.3390/d10040122
Received: 16 September 2018 / Revised: 31 October 2018 / Accepted: 7 November 2018 / Published: 12 November 2018
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Abstract
Pronounced differences exist in the biodiversity and structure of coral reef assemblages with increasing distance from shore, which may be expected given marked cross-shelf gradients in environmental conditions. Cross-shelf variation in the abundance of coral reef organisms is likely to be caused, at [...] Read more.
Pronounced differences exist in the biodiversity and structure of coral reef assemblages with increasing distance from shore, which may be expected given marked cross-shelf gradients in environmental conditions. Cross-shelf variation in the abundance of coral reef organisms is likely to be caused, at least in part, by differences in demography (e.g., growth and survival), though this has rarely been tested. This study quantified growth of three distinct branching coral taxa (Acropora nasuta, Pocillopora spp. and Stylophora pistillata) at six locations on Australia’s Great Barrier Reef (GBR), encompassing inshore, mid-shelf and outer-shelf reefs. Replicate colonies (0–15 colonies per species, per reef) were stained using Alizarin Red in December 2015 and retrieved one year later to quantify linear extension on replicate branches for each colony. Annual linear extension varied within and among coral taxa, with pronounced differences among reefs. For A. nasuta. and S. pistillata, growth rates were highest at one of the inshore reefs, Orpheus Island. However, inter-reef differences in linear extension were not explained by shelf position. Based on differences in skeletal density, which did vary according to shelf position, branching corals at the inshore sites may actually have higher rates of calcification compared to conspecifics on mid-and outer-shelf reefs. This study shows that growth of branching corals is not lower at inshore sites (and perhaps even higher) compared to sites at mid-shelf and outer reefs, despite generally higher levels of sedimentation and turbidity. Full article
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Open AccessArticle The Variable Influences of Sea Level, Sedimentation and Exposure on Holocene Reef Development over a Cross-Shelf Transect, Central Great Barrier Reef
Diversity 2018, 10(4), 110; https://doi.org/10.3390/d10040110
Received: 5 August 2018 / Revised: 25 September 2018 / Accepted: 4 October 2018 / Published: 11 October 2018
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Abstract
Coral reefs globally are impacted by natural and anthropogenic stressors that are compounded by climate change. Understanding past reef responses to natural stressors (cyclones, sea-level change, freshwater inputs, and sedimentation) can provide important insights to further understand recent (within the past century) trends [...] Read more.
Coral reefs globally are impacted by natural and anthropogenic stressors that are compounded by climate change. Understanding past reef responses to natural stressors (cyclones, sea-level change, freshwater inputs, and sedimentation) can provide important insights to further understand recent (within the past century) trends in coral cover and diversity. Here we use a compilation of recently published data to investigate the Holocene development of five fringing reefs that are located on a cross-shelf transect on the central Great Barrier Reef, and that are exposed to varying degrees of natural and anthropogenic sedimentation, storm exposure, and Holocene sea-level change. Forty-two reef cores collected using a combination of manual percussion coring and hydraulic drilling techniques, were analysed and dated using uranium-thorium methods. The chronostratigraphic records of reef development established using 105 recently published radiometric ages and seven new uranium-thorium ages from the reef cores and fossil microatolls preserved across the reef flats were compared to investigate cross-shelf variations in reef development. This is the first study to conduct an internal investigation of reef framework across an inshore–offshore gradient to examine the varying levels of influence of sedimentation, sea level and cyclones. Our observations from the central Great Barrier Reef show that reefs furthest offshore from the mainland coast were typically initiated earliest after the post-glacial marine transgression. Reef flat size, morphology, and growth style varied according to constraints placed on reef development by the composition, depth, shape, and relief of the underlying substrate. We establish that terrigenous sedimentation had a marked effect on the development of inshore reefs closest to the mainland (within 10 km of the mainland coast). Periods of relatively high terrigenous sedimentation correspond with enhanced reef accretion rates, and also resulted in a superior record of palaeo-ecological coral composition (i.e., better preservation) at inshore sites. In contrast, mid-Holocene cyclones played a seemingly more important role in the development of reefs >10 km from the mainland; although cyclones clearly affect reefs closer inshore, their geomorphology is affected by a range of controlling factors. Insights provided by these five Holocene reef chronostratigraphies provide useful baseline understanding of reef condition and growth along a cross-shelf transect where the reefs are exposed to variable stressors. Full article
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