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Future climate trends indicate that changes in temperature and precipitation are likely to influence global supply chains, agricultural productivity, water security, health and well-being; particularly in densely populated nations across the southeast Indian Ocean region. The Indonesian Throughflow is an ocean current that transports low-latitude, warm and relatively fresh water from the western Pacific into the eastern Indian Ocean. It is thought that variability and changes in the Indonesian Throughflow have significant impacts on the climate and oceanography of the Indo-Pacific region. The short coverage of observational records makes assessments of hydrological changes across the region challenging on longer timescales, with changes before the 1970s being particularly unreliable. An extended record of Indonesian Throughflow variability needs to be established to contextualise changes and improve model projections of future variability.Christmas Island, located in the southeast Indian Ocean (not to be confused with the Pacific Ocean Kiritimati Island), is located along an outflow of the Indonesian Throughflow. This Island is an ideal location to develop new palaeo-reconstructions of sea surface temperature and hydroclimate, extending our understanding of Indonesian Throughflow variability. Here we present a newly developed coral palaeoclimate reconstruction for Christmas Island, covering the last 118 years at approximately monthly-fortnightly resolution. Corals are sensitive recorders of critical environmental variables, including sea surface temperature and hydroclimate through the analysis of paired stable oxygen isotopes (δ18O) and trace element (Sr/Ca) ratios. This reconstruction consists of a composite of four newly developed coral records and one previously published record and provides a newly developed δ18Osw variability record for the region. The newly developed δ18Osw coral reconstruction correlates strongly with salinity variability, however, presents a weak relationship to in-situ precipitation, indicating that coral hydroclimate reconstructions from Christmas Island likely isolate salinity variability associated with changes in the strength of the Indonesian Throughflow. This relationship highlights the importance that ocean advection plays on δ18Osw variability at this site. Comparisons to both observational records of the Indonesian throughflow, and previously published coral δ18Osw records from the Ombai Strait (Timor), a major outflow passage, reveal strong relationships to variability at Christmas Island. The Christmas Island reconstruction provides a unique opportunity to extend current knowledge of the Indonesian Throughflow beyond the observational record. This Christmas Island record also provides an opportunity to evaluate the impact that interannual to multidecadal variability has on the climate across the southeast tropical Indian Ocean.

Understanding the drivers of net coral reef calcium carbonate production is increasingly important as ocean warming, acidification, and other anthropogenic stressors threaten the maintenance of coral reef structures and the services these ecosystems provide. Despite intense research effort on coral reef calcium carbonate production, the inclusion of a key reef forming/accreting calcifying group, the crustose coralline algae (CCA), remains challenging both from a theoretical and practical standpoint. While corals are typically the primary reef builders of today, ongoing declines in coral cover due to a range of environmental perturbations will likely increase the relative importance of CCA and other non-scleractinian calcifying taxa to coral reef carbonate production. Here, we demonstrate that CCA are important carbonate producers that, under certain conditions, can match or even exceed the contribution of corals to coral reef carbonate production. Despite their importance, CCA are often inaccurately recorded in benthic surveys or even entirely missing from coral reef carbonate budgets. We outline several recommendations to improve the inclusion of CCA into such carbonate budgets under the ongoing climate crisis.

The use of X-Ray Fluorescence (XRF) Core Scanning for continuous high-resolution analysis of Sr/Ca in corals is investigated here as a new method for analyzing coral material. Corals are valuable archives for generating high resolution palaeoclimate records of sea surface temperatures of the tropical oceans, but traditional methods of analyzing coral geochemistry involve extensive subsampling and wet chemistry techniques to obtain high precision elemental records. More recent developments of micro-beam techniques have limitations in the length of core that can be scanned at any one time. XRF core scanning provides a fast, non-destructive method of analyzing long sections of coral cores whilst maintaining a high sampling resolution. Here we apply this method to two modern corals, from the Sunda Strait, Indonesia and One Tree Island, Great Barrier Reef Australia. We find that results show that XRF core scanning of corals produce Sr/Ca records that capture the annual cycle, particularly from reef sites with a large sea surface temperature range. Coupled density measurements of the coral skeleton also aid in increasing the utility of XRF measurements obtained from coral material, although difficulties remain in reliably reconstructing interannual temperature variability using XRF Sr/Ca determinations. We recommend that XRF can provide a valuable method of quick and non-destructive screening of coral material, prior to more targeted analysis using traditional destructive geochemical analysis.

We detail the benthic compositon of the turbid-water coral reefs of Tobago in 2016 and examine the influence of mass coral bleaching and hydro-geomorphic setting (sheltereted vs. wave-exposed) on benthic community dynamics against the 2007 baseline. In the current assessment mean hard coral cover was 14.83% ± 0.85, which ranged from 2% to 37% with few sites exceeding 20%. Mean macroalgal cover was low (6.04% ± 0.61) with most sites experiencing less than 8% macroalgal cover. Differences in benthic cover between sheltered and wave-exposed settings were mainly driven by contrasts in proportions of sponge, macroalgae and Orbicella faveolata corals. Linear mixed-effects modelling suggests stability in hard coral cover and decline in macroalgal cover across sites against the 2007 baseline. Significant spatio-temporal interactions were observed for soft coral and CTB (crustose coralline algae, turf algae and bare substrate). Overall, hard coral cover appears to have declined at some sites and macroalgal cover to have increased at other, but there is no evidence of widespread regime shift. While the hydro-geomorphic setting had a significant but weak effect (R > 0.3) on observed spatial and temporal patterns, our findings suggest that sheltered settings were less predisposed to macroalgal overgrowth compared to wave-exposed areas. In the era of climate change, targeted management should focus on strategies that mitigate macroalgal overgrowth, promote hard coral stability (or resilience) while preventing further loss.

Coral reefs provide critical ecological and geomorphic (e.g. sediment production for reef-fronted shoreline maintenance) services, which interact in complex and dynamic ways. These services are under threat from climate change, requiring dynamic modelling approaches that predict how reef systems will respond to different future climate scenarios. Carbonate budgets, which estimate net reef calcium carbonate production, provide a comprehensive ‘snap-shot’ assessment of reef accretionary potential and reef stability. These budgets, however, were not intended to account for the full suite of processes that maintain coral reef services or to provide predictive capacity on longer timescales (decadal to centennial). To respond to the dual challenges of enhancing carbonate budget assessments and advancing their predictive capacity, we applied a novel model elicitation and review method to create a qualitative geo-ecological carbonate reef system model that links geomorphic, ecological and physical processes. Our approach conceptualizes relationships between net carbonate production, sediment transport and landform stability, and rates knowledge confidence to reveal major knowledge gaps and critical future research pathways. The model provides a blueprint for future coral reef research that aims to quantify net carbonate production and sediment dynamics, improving our capacity to predict responses of reefs and reef-fronted shorelines to future climate change.

The continued health and function of tropical coral reefs is highly dependent on the ability of reef-building organisms to build large, complex, three-dimensional structures that continue to accrete and evolve over time. The recent deterioration of reef health globally, including loss of coral cover, has resulted in significant declines in architectural complexity at a large, reef-scape scale. Interestingly, the fine-scale role of micro-structure in initiating and facilitating future reef development and calcium carbonate production has largely been overlooked. In this study, experimental substrates with and without micro-ridges were deployed in the lagoon at One Tree Island for 34 months. This study assessed how the presence or absence of micro-ridges promoted recruitment by key reef-building sclerobionts (corals and encrusters) and their subsequent development at micro (mm) and macro (cm) scales. Experimental plates were examined after 11 and 34 months to assess whether long-term successional and calcification processes on different micro-topographies led to convergent or divergent communities over time. Sclerobionts were most prevalent in micro-grooves when they were available. Interestingly, in shallow lagoon reef sites characterised by shoals of small parrotfish and low urchin abundance, flat substrates were also successfully recruited to. Mean rates of carbonate production were 374 ± 154 (SD) g CaCO3 m−2 yr−1 within the lagoon. Substrates with micro-ridges were characterised by significantly greater rates of carbonate production than smooth substrates. The orientation of the substrate and period of immersion also significantly impacted rates of carbonate production, with CaCO3 on cryptic tiles increasing by 28% between 11 and 34 months. In contrast, rates on exposed tiles declined by 35% over the same time. In conclusion, even at sites characterised by small-sized parrotfish and low urchin density, micro-topography is an important settlement niche clearly favouring sclerobiont early life-history processes and subsequent carbonate production.

This research was supported by ARC DECRA grants DE160100092 and DE120101998, and the NCI National Facility.

Artificial substrates are routinely used in coral reef research to model the recruitment and growth responses of benthic organisms (e.g. coral recruitment and encrusting organisms) to environmental change. Two commonly used, but structurally different, artificial substrates include cylindrical PVC pipes and flat ceramic tiles. Various ecosystem based models extrapolate data from these substrates interchangeably based on the assumption that results are directly comparable. In order to test this assumption we deployed these commonly used artificial substrate materials, PVC poles and ceramic tiles, in shallow patch reefs for 34 months at One Tree Island, Great Barrier Reef. Tiles were positioned to mimic upwards facing, well-lit substrates (exposed), and downwards facing, shaded (cryptic) substrates. Multivariate analyses demonstrated that the community composition differed significantly between all three treatments. The majority of artificial substrate, coral reef experiments focus on key groups of calcifying organisms, primarily: coralline algae, scleractinian coral and/or total calcareous encruster cover. Interestingly, significant differences in the recruitment, colonisation and community composition of these organisms were detected for our three treatments. When compared to ceramic tiles, PVC poles had greater coverage of crustose coralline algae but reduced levels of coral recruits (

Tropical coral reef monitoring relies heavily on in situ diver observations. However, in many reef regions resources are not available to regularly monitor reefs. This lack of historical baseline data makes it difficult to determine how different reefs respond to environmental stressors and what the implications are for management. To test whether coral cores could be used to identify bleaching events retrospectively, three sites in Tobago with pre-existing reef data including water quality and bleaching observations were identified. Colpophyllia natans cores were examined for growth anomalies which occurred during periods of thermal stress. If present, anomalies were compared to in situ, real-time bleaching observations and water quality data. Interestingly, sites with better water quality during the 2005 thermal anomaly were less prone to bleaching. We suggest that by reducing terrestrial run-off (e.g., sediment and nutrients), and therefore improving marine water quality, reef managers could enhance near-shore coral reef resilience during high-temperature events.

Coral reefs are consolidated calcium carbonate (CaCO3) platforms built over hundreds of thousands of years by calcifying organisms including corals, encrusting algae and invertebrates. The geomorphic integrity of coral reefs depends on the carbonate budget, which quantifies the net gain or loss of calcium carbonate, given additive and removal processes. Here, we construct three carbonate budgets for Cocos (Keeling) atoll in the East Indian Ocean from seafloor records of carbonate producers before, during and after a coral bleaching event (2015–2017). A satellite image is used to upscale 367 in-situ observations across the complete atoll (are 225 km2). Growth of calcifying encrusters is monitored on settlement plates from 2015 to 2016, while bioerosion is quantified from parrotfish surveys and macroborer analysis of rubble. The highest rates of production were on the outer atoll forereef and in the northern lagoon (1.5 and 1.61 kg m−2 yr−1 respectively). The forereef produced an order of magnitude more calcium carbonate (approximately 13,114 t per year in 2015) than the other zones due to a high coverage of live branching coral (ca 50%) combined with a large forereef area (123 km2). The greatest rates of removal occurred on the shallow forereef (−1.67 kg m−2 yr−1) driven largely by Bolbometopon muricatum parrotfish bioerosion, resulting in a net loss of carbonate in 2017 (−0.15 kg m−2 yr−1). Accounting for parrotfish bioerosion, the net atoll budget was estimated to be 5976 t of calcium carbonate in 2015, which reduced by 46% over the coral bleaching period to 3200 t in 2017. Compared to other Indian Ocean reefs, this is a relatively minor impact of coral bleaching on the carbonate budget at Cocos (Keeling) atoll.

Coral cores were collected along an environmental and water quality gradient through the Whitsunday Island group, Great Barrier Reef (Australia), for trace element and stable isotope analysis. The primary aim of the study was to examine if this gradient could be detected in coral records and, if so, whether the gradient has changed over time with changing land use in the adjacent river catchments. Y/Ca was the trace element ratio which varied spatially across the gradient, with concentrations progressively decreasing away from the river mouths. The Ba/Ca and Y/Ca ratios were the only indicators of change in the gradient through time, increasing shortly after European settlement. The Mn/Ca ratio responded to local disturbance related to the construction of tourism infrastructure. Nitrogen isotope ratios showed no apparent trend over time. This study highlights the importance of site selection when using coral records to record regional environmental signals.

The biodiversity of coral reefs is dominated by invertebrates. Many of these invertebrates live in close association with scleractinian corals, relying on corals for food, habitat or settlement cues. Given their strong dependence on corals, it is of great concern that our knowledge of coral associated invertebrates is so limited, especially in light of severe and ongoing degradation of coral reef habitats and the potential for species extinctions. This review examines the taxonomic extent of coral-associated invertebrates, the levels of dependence on coral hosts, the nature of associations between invertebrates and corals, and the factors that threaten coral-associated invertebrates now and in the future. There are at least 860 invertebrate species that have been described as coral associated, of which 310 are decapod crustaceans. Over half of coral-associated invertebrates appear to have an obligate dependence on live corals. Many exhibit a high degree of preference for one or two coral species, with species in the genera Pocillopora, Acropora and Stylophora commonly preferred. This level of habitat specialization may place coral-associated invertebrates at a great risk of extinction, particularly because preferred coral genera are those most susceptible to coral bleaching and mortality. In turn, many corals are also reliant on the services of particular invertebrates, leading to strong feed backs between abundance of corals and their associated invertebrates. The loss of even a few preferred coral taxa could lead to a substantial decline in invertebrate biodiversity and have far-reaching effects on coral reef ecosystem function. A full appreciation of the consequences of further coral reef degradation for invertebrate biodiversity awaits a more complete description of the diversity of coral-associated invertebrates, the roles they play in coral reef ecosystems, their contribution to reef resilience and their conservation needs.

The number of no-take marine protected areas (here referred to as no-take areas, NTAs) on coral reefs has increased considerably in recent decades. coincident with accelerating degradation of coral reefs, expectations of the benefits that NTAs can provide for coastal societies and sustainability of marine ecosystems has grown. These include increasing abundance of reef organisms both inside and outside NTAs, protecting key ecosystem functions, and providing social and economic benefits through improved fisheries and tourism. However, there is a lack of convincing evidence for many of these expectations. This is the first attempt to synthesize all potential costs and benefits of coral reef NTAs and critically examine evidence of their impacts on both ecosystems and societies. NTAs with high compliance consistently increase the diversity, density and biomass of exploited reef fishes and certain groups of motile invertebrates within their boundaries and have benefits for reef-associated tourism. Some NTAs provide small increases in the abundance of cor- als and decreases in macroalgal cover. The effects of NTAs on genetic diversity and connectivity among meta-populations are variable or as yet unquantified. There is limited evidence of NTAs providing social benefits through increased fishery yields and tourism revenue. There are examples of both positive and negative effects on social well-being. Finally, sharks, marine megafauna and microbial communities showed few tangible benefits from NTAs. Substantial gaps in the science of coral reef NTAs remain, especially in their capacity to provide socioeconomic benefits. A crucial research priority is understanding how the cumulative effects of climate change will influence the various benefits that NTAs provide. To be effective, NTAs must be used in conjunction with a range of other management tools and applied according to local environmental and societal contexts.

1. The adaptive radiation of fishes into benthic (littoral) and pelagic (lentic) morphs in post-glacial lakes has become an important model system for speciation. Although these systems are well studied, there is little evidence of the existence of morphs that have diverged to utilize resources in the remaining principal lake habitat, the profundal zone. 2. Here, we tested phenotype-environment correlations of three whitefish (Coregonus lavaretus) morphs that have radiated into littoral, pelagic and profundal niches in northern Scandinavian lakes. We hypothesized that morphs in such trimorphic systems would have a morphology adapted to one of the principal lake habitats (littoral, pelagic or profundal niches). Most whitefish populations in the study area are formed by a single (monomorphic) whitefish morph, and we further hypothesized that these populations should display intermediate morphotypes and niche utilization. We used a combination of traditional (stomach content, habitat use, gill raker counts) and more recently developed (stable isotopes, geometric morphometrics) techniques to evaluate phenotype-environment correlations in two lakes with trimorphic and two lakes with monomorphic whitefish. 3. Distinct phenotype-environment correlations were evident for each principal niche in whitefish morphs inhabiting trimorphic lakes. Monomorphic whitefish exploited multiple habitats, had intermediate morphology, displayed increased variance in gillraker-counts, and relied significantly on zooplankton, most likely due to relaxed resource competition. 4. We suggest that the ecological processes acting in the trimorphic lakes are similar to each other, and are driving the adaptive evolution of whitefish morphs, possibly leading to the formation of new species.

Background:The rising temperature of the world’s oceans has become a major threat to coral reefs globally as the severityand frequency of mass coral bleaching and mortality events increase. In 2005, high ocean temperatures in the tropicalAtlantic and Caribbean resulted in the most severe bleaching event ever recorded in the basin.Methodology/Principal Findings:Satellite-based tools provided warnings for coral reef managers and scientists, guiding both the timing and location of researchers’ field observations as anomalously warm conditions developed and spread across the greater Caribbean region from June to October 2005. Field surveys of bleaching and mortality exceeded prior efforts in detail and extent, and provided a new standard for documenting the effects of bleaching and for testing nowcast and forecast products. Collaborators from 22 countries undertook the most comprehensive documentation of basin-scale bleaching to date and found that over 80% of corals bleached and over 40% died at many sites. The most severe bleaching coincided with waters nearest a western Atlantic warm pool that was centered off the northern end of the Lesser Antilles.Conclusions/Significance:Thermal stress during the 2005 event exceeded any observed from the Caribbean in the prior 20 years, and regionally-averaged temperatures were the warmest in over 150 years. Comparison of satellite data against field surveys demonstrated a significant predictive relationship between accumulated heat stress (measured using NOAA CoralReef Watch’s Degree Heating Weeks) and bleaching intensity. This severe, widespread bleaching and mortality willundoubtedly have long-term consequences for reef ecosystems and suggests a troubled future for tropical marine ecosystems under a warming climate NOAA Coral Reef Conservation Program Article Nr: e13969

Knowledge of coral recruitment patterns helps us understand how reefs react following major disturbances and provides us with an early warning system for predicting future reef health problems. We have reconstructed and interpreted historical and modern-day recruitment patterns, using a combination of growth modelling and in situ recruitment experiments, in order to understand how hurricanes, storms and bleaching events have influenced coral recruitment on the Caribbean coastline of Tobago. Whilst Tobago does not lie within the main hurricane belt results indicate that regional hurricane events negatively impact coral recruitment patterns in the Southern Caribbean. In years following hurricanes, tropical storms and bleaching events, coral recruitment was reduced when compared to normal years (p = 0.016). Following Hurricane Ivan in 2004 and the 2005–2006 bleaching event, coral recruitment was markedly limited with only 2% (n = 6) of colonies estimated to have recruited during 2006 and 2007. Our experimental results indicate that despite multiple large-scale disturbances corals are still recruiting on Tobago’s marginal reef systems, albeit in low numbers.

AUSTRALIANS have pretty much all the science we need to conserve our landscapes, what lacks is the will and motivation to make it happen. This book challenges the assumption of many conservationists that science is, or should be the primary consideration in land management. Instead conservation is presented as a value — an impulse. Science is a key facet but no more important than the culture, history, economy or social context of the people and the place. Reading a bit like an extended National Geographic article, the book is presented in four parts entitled “Place”, “Landscape”, “Biodiversity” and “Livelihood”. Between each part is an artistic interlude of illustrations and within each chapter are standalone sidebars, captioned images and a soundtrack — the collective work of almost 50 contributors from diverse backgrounds and varying interests. The academic imperative to reference has been retained, but not in the heavy-handed scientific style. Each piece has a feeling of individuality; “this is where I come from, this is my experience, this is what I have learned and this is what I think.” Scientists are well represented amongst the contributors, but the scientific method is afforded no special prominence. The book is a collection of stories by self-professed conservationists — historians, biologists, painters, pastoralists, activists, palaeontologists, sociologists, traditional owners, photographers, students, agronomists, anthropologists, journalists, poets, public servants, archaeologists and more.