Scleractinian Corals Research Articles

“Accidental” artificial reefs — lessons from Singapore for coral and seagrass restoration along urban shorelines

Due to rapid urbanization and coastline modification, the city-state of Singapore has lost nearly three-quarters of its intertidal coral reef area and nearly 90% of its subtidal coral reef area since pre-colonial times. However, the recolonization of coral communities has occurred naturally on seawall structures despite the lack of any deliberate planning or intervention. Recent mapping of coastal habitats shows that seawall reefs now form a significant proportion of habitat occupied by hard corals in Singapore, including areas where there were historically no coral reefs, and often exist side-by-side with other regenerated marine habitats such as seagrass meadows. These “accidental” artificial reefs demonstrate that new hard coral and seagrass communities can establish along highly urbanized shorelines, albeit in a novel form, and provide ecosystem services to urban communities. Key lessons can be drawn from these case studies, particularly relating to landscape design of urban shorelines to facilitate ecological coral and seagrass restoration. These include constructing seawalls with optimal slope profiles, providing creviced berms at the lower intertidal of seawalls, co-locating seawalls with artificial intertidal lagoons, and considering coral larvae supply in choosing sites for restoration using seawalls. Most importantly, these case studies illustrate the potential of using seawalls to restore hard coral and seagrass habitat on a landscape-scale, especially in urban environments.

Dining on corals: stable isotope evidence for close trophic connection between gall crabs (Cryptochiridae) and their stony coral hosts

The exact nature of the relationship between symbiont fauna and their hosts is often unclear, but knowing more about these intricate ecological interactions is vital to understand the trophic positions of host-associated fauna, and can aid in accurate constructions of food-webs on coral reefs. Scleractinian corals are hosts to hundreds of symbiont taxa, including fish and many invertebrate species. Some of these associated fauna are beneficial to their coral host(s), whereas other taxa can have detrimental effects, yet their impact is often difficult to determine. Coral-dwelling gall crabs (Cryptochiridae) are obligate, often host-specific, symbionts of scleractinian corals but the nature of this relationship is still under debate. Three Atlantic gall crab species (Kroppcarcinus siderastreicola, Opecarcinus hypostegus and Troglocarcinus corallicola) and their coral hosts’ tissue/mucus were collected from reefs in Guadeloupe. Stable carbon and nitrogen isotope values were measured for 57 crabs inhabiting host coral colonies belonging to seven different coral species (although only 27 colonies from five coral species were collected), alongside other potential food sources (epilithic algal matrix, plankton and particulate organic matter). The carbon and nitrogen isotope values of gall crabs relative to those of their respective coral host(s) and other possible food sources showed that coral tissue/mucus was the main food source for the crabs. The results of the mixing models further supported this finding, suggesting that corals are responsible for 40–70% of the crabs’ diet. In T. corallicola, the isotopic signature differed significantly between sexes, possibly caused by the high sexual dimorphism observed in this species. Here we showed that Atlantic gall crabs mainly dine on coral tissue and/or mucus excreted by their coral hosts, highlighting their nutritional dependence on their host. However, since coral mucus is continuously exuded by scleractinians, hence the energetic or metabolic drain for corals is expected to be minimal. Gall crabs depend on their coral hosts for settlement cues as larvae, for habitat as adults and - highlighted by this study - for food, essential for their subsistence. This obligate dependence on their hosts for all parts of their life makes them extremely vulnerable to reef degradation, and underlines the importance in understanding the exact nature of a relationship between symbiont and coral host.

Marvellous Maastrichtian miners – bioerosional trace fossils as natural casts from the type area of the Maastrichtian Stage, the Netherlands

Abstract Over recent decades, the type area of the Maastrichtian Stage in southern Limburg (the Netherlands) and contiguous Belgian territory, and the former ENCI-HeidelbergCement Group quarry (Sint-Pietersberg, Maastricht) in particular, has yielded an exquisitely preserved ichnocoenosis of bioerosional trace fossils, mainly preserved as natural casts in scleractinian corals. More than 20 ichnospecies are here documented, the majority from the type Maastrichtian for the first time. These ichnotaxa constitute a good record of successive colonisation sequences; the present bioerosional ichnocoenosis is regarded to belong to the Entobia ichnofacies.

Distribution and palaeoecology of scleractinian corals during the Maastrichtian (Late Cretaceous)

Abstract Maastrichtian scleractinian corals from 94 localities in 26 Maastrichtian regions world-wide with strata of that age are taxonomically and palaeobiogeographically evaluated. A total of 205 taxa, belonging to 116 genera and 37 families, are included in the present study. Most coral taxa have been recorded from non-reefal environments. A significant majority of these taxa (genera = 70.7%; species = 75.6%) appear to have been endemic during the Maastrichtian. The Maastrichtian coral fauna is dominated by solitary and cerioid-plocoid forms (both accounting for 41 genera = 70%), having mainly medium- and large-sized corallites. The most diverse coral assemblages are those that have been recorded from arid (Jamaica: 63 species, Mexico: 29 species), warm-temperate (the Netherlands-Belgium: 32 species) and tropical regions (Iran: 27 species). The occurrence of Cunnolites polymorphus (Goldfuss) is newly recorded for the Netherlands (southern Limburg). Compared to the microstructural composition of the coral fauna of the lowermost Cretaceous (Berriasian; 91% of the species and 83% of the genera belonged to previously established microstructural groups), in the Maastrichtian, corals belonging to previously established microstructural groups were of minor importance (genera = 26%; species = 29.3%). The majority of Maastrichtian scleractinian taxa (both solitary and colonial) from the type area of the Maastrichtian Stage in the southeast Netherlands and northeast Belgium are illustrated.

Retailer perspectives reveal knowledge gaps in the traceability of the scleractinian coral trade in Singapore

Scleractinian corals are key reef-builders in tropical marine ecosystems. Harvests of wild stocks for the global marine aquarium trade have raised concerns about unsustainable exploitation. While it is important to ensure that marine ornamental species are used legally and sustainably, it is challenging to trace them through the trade due to the fragmented and complex supply chain. Retailers can provide unique perspectives to narrow knowledge gaps as they interact closely with both suppliers and consumers. Through semi-structured interviews of retailers based in Singapore, we investigated their knowledge of the supply chain, trade practices, and consumer preferences. We also surveyed taxa available for sale at these brick-and-mortar aquarium shops. Our study revealed at least 42 genera from 14 families of scleractinian corals present across 20 shops in Singapore. Retailers displayed a lack of familiarity in coral provenance and trade regulations, suggesting that they have limited awareness of traceability along the supply chain. Import decisions were not guided by traceability and environmental sustainability, but instead were driven by demand and supply factors such as aesthetics, rarity, and availability. This underscores the need for more outreach and engagement efforts to raise awareness among commercial stakeholders towards improving traceability and sustainable management in the marine aquarium industry.

Variable prevalence of diseases and compromised health conditions on hard corals around Mauritius Island, Western Indian Ocean

Although coral diseases and compromised health conditions (CHCs) are one of the most prominent threats to coral reefs globally, they have yet to be thoroughly investigated in the Western Indian Ocean. This study aimed to assess the prevalence and spatial distribution of coral diseases and CHCs around Mauritius. Six coral diseases [Growth Anomaly (GA), Skeletal Eroding Band (SEB), Brown Band (BrBD), Porites White Patch Syndrome (PWPS), White Syndromes (WSs), and Yellow Band (YB)] and four CHCs [Pink Patches (PP), Pink Spots (PS), Pink Line Syndrome (PLS), and Focal Bleaching (FB)] were spatially variable in prevalence among the 17 studied sites. The average prevalence for Mauritius was 4.88% (SD 0.52%), almost half of what has been documented from Caribbean and Pacific reefs (about 10%). Total coral colony density (R = −0.585, P < 0.001) and diseases/CHCs-affected host density (R = −0.249, P > 0.05) were negatively correlated while human population density (R = 0.085, P < 0.05) and coral cover (R = 0.045, P < 0.05) were positively correlated with coral diseases/CHCs prevalence. The prevalence of diseases/CHCs significantly differed between the reef-flat and fore-reef zones, with the latter exhibiting higher prevalence. Cluster analyses revealed that PLS, YB, and FB were mostly distributed in the fore-reef zone, while the other diseases/CHCs were mostly predominant on the reef-flats. However, coral disease/CHCs prevalence did not differ significantly (F = 2.613, P > 0.05) between protected and nonprotected zones. These findings have important implications for informing appropriate coral reef conservation and management strategies for Mauritius.

Fish and coral assemblages of a highly isolated oceanic island: The first eDNA survey of the Ogasawara Islands

AbstractThe Ogasawara Islands are a highly isolated oceanic archipelago in the Pacific Ocean that possess unique faunal and floral biodiversity with a high level of endemism. As historically more focus has been put on the terrestrial realm in examining diversification and evolutionary processes on oceanic islands, publicly accessible and spatially resolved data of marine reef ecosystems remain scarce. To address this issue, we conducted the first environmental DNA (eDNA) metabarcoding surveys of the actinopterygian (ray‐finned) and elasmobranch fishes and of Scleractinia coral assemblages in the waters of the Ogasawara Islands. We detected a total of 124 unique taxa of fish and 38 unique taxa of scleractinian corals. Overall, our eDNA results confirmed that the Ogasawara Islands host a rich variety of coral and fish fauna and underline the strength of eDNA surveys in rapidly obtaining targeted multi‐taxa data using seawater samples, requiring comparatively little effort and a lack of requirement for in situ taxonomic expertise. We anticipate that continued biomonitoring using eDNA with high sampling effort will add to and complement the body of knowledge regarding species distributions, invasive species, and biodiversity hotspots within oceanic archipelagos.

Diversity patterns of the South African azooxanthellate scleractinians (Cnidaria: Anthozoa), with considerations of environmental correlates.

Azooxanthellate scleractinian corals, a group of species that lack a symbiotic relationship with dinoflagellates, are influenced by environmental variables at various scales. As the global commitment to sustainably manage ocean ecosystems and resources rises, there is a growing need to describe biodiversity trends in previously unsampled areas. Benthic invertebrate research in South Africa is a developing field, and many taxa in deep water environments remain inadequately characterized. Recently, the South African azooxanthellate scleractinian fauna was taxonomically reviewed, but their distributional correlations with physical parameters have not been studied. Here we aim to understand the biodiversity gradients of the South African azooxanthellate coral fauna by analysing the environmental correlates of museum samples. The associated coordinate data were georeferenced and depth obtained from a national bathymetric dataset, prior to undertaking a multivariate analysis. This analysis encompassed several steps, including the grouping of the longitude and depth data (environmental data), identifying families characteristic of the group variability, and examining the correlation of the associated data with the biological data. Additionally, the analysis involved quantifying diversity patterns along the environmental gradients. Overall, our results confirmed two longitudinal groups (eastern margin [Group A] vs southern and western margin [Group B]) and 11 depth categories represented within two bathymetric zones (shallow [50-200 m] and deep [300-1000 m]). Caryophylliids, flabellids, and dendrophylliids contributed the most towards distinguishing longitudinal and depth gradients. Both abiotic variable (longitudinal and depth) partially explained coral distribution patterns, with depth being highly correlated to the species variation observed. Data limitations within our data set resulted to unexplained variance, however, despite these limitations, the study demonstrates that historical museum samples provide a valuable data source that can fill research sampling gaps and help improve the understanding of biodiversity patterns of the coral fauna in under sampled marine ecosystems.

Coral-mimetic production of aragonite films from CO2 captured by biogenic polyamines

We designed CaCO3 films comprised of aragonite nanorods by mimicking the microstructure and the formation process of the calcareous skeleton of a stony coral in the sea.

Amplification of Immune Genes in Ancient Stony Corals for Adapting to Unstable Marine Environments

The Late Devonian period was known for disturbances such as lower temperatures and abnormal ocean carbon and nitrogen levels, leading to the extinction of approximately 21% of genus-level and 16% of family-level marine organisms. However, evolutionary responses of marine organisms to hardships have not yet been fully explored, even though these organisms may soon face another extinction event. Stony corals, one of the few marine organisms that survived the Late Devonian Period, may provide some insight into the adaptive evolution mechanism underlying survival in unstable marine environments. The current study revealed that the gene families related to signal transduction and immunity, such as G protein-coupled receptors and Toll-like receptors, expanded in stony coral ancestors (SCAs), possibly improving the efficiency of stress and immune responses and maintaining internal environmental homeostasis. Interestingly, the first horizontal gene transfer event of MSHA from actinomycetes to corals and the subsequent expansion in SCAs were discovered. MSHA encodes D-inositol 3-phosphate glycosyltransferase, which is naturally found in actinomycetes and is responsible for the synthesis of mycothiol with antibacterial properties. The MSHA family members diverged throughout the development of stony corals, but their essential function in glycosyl transfer remained unchanged. Therefore, the evolutionary history of ancient coral shows that efficient signal transduction and increased immunity may have driven the survival of SCAs throughout the Late Devonian period, which may provide new insights into how current corals avoid extinction.

Effectiveness of coral (Bilbunna) relocation as a mitigation strategy for pipeline construction at Hayman Island, Great Barrier Reef

SummaryCoral reef management techniques such as relocation and transplantation are increasingly implemented in the context of increasing coastal development and a global decline of coral reefs over the last 30 years. A 170 m submarine desalination pipeline was constructed in 2020 to discharge wastewater from the desalination plant for Hayman Island resort, Whitsundays, Queensland, Australia. Pre‐construction site assessments were conducted indicating a healthy, diverse and recovering coral community between intertidal and 12 m depth in the proposed route of the pipeline. Mitigation options included the selection of a pipeline route that minimised impact on coral, and relocation and transplantation of hard corals. Two hundred and four corals comprising 35 species from 15 genera, with estimated sizes ranging from small (less than 2 kg) to extra large (over 50 kg), were relocated from the pipeline footprint to a similar nearby site. The estimated total weight of relocated corals was 873–2850 kg. The most common species transplanted were Hump Coral (Porites lutea) (27%), Lesser Star Coral (Goniastrea aspera) (8.3%) and Starflower Coral (Astreopora ocellata) (7.8%). Individual coral survivorship and growth was monitored at zero, one, six, 12 and 24 months. After 24 months total coral survival was 77.5%. The survivorship of relocated coral exceeded the mean for global coral restoration projects and was deemed successful by the regulator. To assist benchmarking of future coral relocation projects we propose a standard of below 50% as poor, 50–60% as below average, over 60% as acceptable and over 80% coral survival at two years as excellent.

Distribution of Coral Diseases and Compromised Health Abundance in The Eastern Coastal Water of Kei Besar Island, Southeast Maluku

Coral diseases are caused by bacteria, fungi, or viruses due to stress or compromised health in the aquatic environment. This study identifies the abundance of coral diseases and compromised health in Kei Besar Island, Southeast Maluku. Data was collected using the Belt Transect method at six locations. 224 hard coral colonies were affected by eleven life forms and nine genera of coral disease, while 2172 hard coral colonies were affected by eleven life forms and 47 genera of compromised health. Coral Massive (CM) life form and Porites genus were the most affected. Six types of coral diseases and nine types of compromised health were identified. Kilwait and Ngefuit Bawah had the highest abundance of hard coral colonies affected by coral disease and compromised health, respectively.

Benthic and fish community composition on mesophotic reefs in Grand Cayman.

Mesophotic Coral Ecosystems (MCEs) represent unique ecological habitats that range from 30 to 150 m deep, harbouring phylogenetically distinct species and offering refuge for many taxa during times of environmental stress. Yet owing to inaccessibility of ecosystems at these depths, most MCEs remain unexplored, with quantifications of ecological communities in these habitats lacking across many regions. Here, using open- and closed-circuit technical diving, we quantified benthic and fish community composition at four mesophotic reef sites (45 m depth) in Grand Cayman. We show significant differences in benthic community composition over a small spatial scale driven by disparate coverage of sponges, crustose coralline algae, and sand/rubble, yet consistent patterns of macroalgal dominance representing >50% coverage at each site and low hard coral cover at an average of 2.4%. Reef fish species richness, biomass, and density was consistent across sites, however the relative contribution of individual species to community composition differed significantly. Macrocarnivores were found to be the dominant contributors to biomass, with invertivores the most speciose, and omnivores and planktivores at the highest densities, consistent with previous descriptions of mesophotic fish assemblages in other regions. Similarly, the low hard coral cover and high macroalgae and sponge cover of the benthic communities also appear ecologically similar to several described mesophotic reefs yet is not uniform across the Caribbean. The ecological organisation of Grand Cayman's MCEs may result from a variety of factors such as isolation from other major land masses, geology, local geography, and anthropogenic activity at both the local and global scale and highlight the importance of continued exploration and documentation of MCE communities.

Method for Calculating the Coral Health Index (Case Study: Mapur Island, Bintan, Indonesia)

This study evaluates the health and condition of coral reefs in the Mapur Island - Bintan Conservation Area, located in the Riau Islands Province, Indonesia. The research was conducted at 5 site locations using the Underwater Photo Transect (UPT) method, with a focus on hard coral cover and the Coral Health Index (CHI). Coral lifeform data were analyzed using Coral Point Count with Excel extensions (CPCe) software. The results revealed significant variability in coral cover, ranging from 14.47% to 59.27%, with an average of 39.36%, placing the coral reefs in the “Moderate” category. However, despite high hard coral cover at some sites, coral health varied, with certain locations exhibiting significant disease prevalence. Among the 5 sites surveyed for CHI, four were classified as “healthy,” while one were categorized “diseased.” Statistical analyses, including Welch’s t-test and Bayesian inference, indicated no significant difference between the CHI and hard coral cover, suggesting that high coral cover does not necessarily imply a healthier reef. Diseases such as Pink- Blotch Syndrome, Black Band Disease, and White Syndrome were prevalent across several sites, highlighting the influence of environmental stressors on coral health. The study underscores the importance of regular coral health monitoring and the need for conservation efforts to mitigate the impact of coral diseases and climate change. These findings provide crucial insights into the status of coral reefs in the Mapur Island - Bintan Conservation Area and contribute to broader efforts to preserve marine biodiversity.

Loss of Coral Reefs due to Ship Grounding in Indonesian Water: Case Study on Karimun Jawa National Park (TNKj)

A ship grounding on coral reefs can cause severe physical and biological damage, including coral dislodgement and removal, skeleton destruction, sediment erosion, and loss of three-dimensional complexity. The event of a ship grounding in Karimunjawa National Park caused live coral degradation of 100% and massive damage to foliose and branched coral. The total loss of hard coral biodiversity reached 261,274 colonies in an area of ±2687.87 square meters. This destruction has reduced the biodiversity of coral reefs, necessitating urgent conservation and restoration efforts in the affected area. The specific data provided, such as variations in population and density, helps provide a comprehensive understanding of the ecological damage caused by the ship grounding.

Biochemical Adaptability of the Relationship between Tropical Hard Corals and Photosynthetic Symbiotic Algae under Climate Change

Biochemical Adaptability of the Relationship between Tropical Hard Corals and Photosynthetic Symbiotic Algae under Climate Change

Evaluation of Coral Reef Health Status in the Fish Sanctuary of San Esteban, Ilocos Sur

Studies on corals are lacking in Ilocos Sur’s marine protected areas (MPAs), hindering management effort development. This study evaluated the health status of coral reefs in the San Esteban Fish Sanctuary. Hard coral cover, hard coral diversity in terms of Taxonomic Amalgamation Units (TAUs), and coral reef health status in terms of live coral coverage, algae coverage, sand coverage, and coral mortality index were measured in two sampling stations inside an over-a-decade-old fish sanctuary that does not have previous data on its coral reef health status. The Underwater Photo Transect (UPT) method was employed to take image samples subjected to the Coral Point Count with Excel extensions (CPCe) software for analysis. The study revealed that the coral reef in San Esteban Fish Sanctuary is in good condition with a hard coral cover of 30.0%, falls under Hard Coral Cover Category C, and a hard coral diversity of 16.8TAUs that falls under Diversity Category D. The fish sanctuary is also in a healthy condition based on excellent live coral coverage, algae coverage, sand coverage, and low coral mortality index. The two stations are more or less the same in terms of the aforementioned parameters. Overall, it is recommended to continuously strengthen the enforcement of the fish sanctuary to protect its coral reefs, measure other parameters that might impact and indicate coral reef health status, employ evaluations inside and outside MPAs in the province, and use high-resolution cameras during image sampling for more efficient analysis.

Considering biotic interactions exacerbates the predicted impacts of climate change on coral‐dwelling species

AbstractAimClimate change is affecting the geographic distributions of many species and researchers are increasingly relying on species distribution models (SDMs) to forecast species' redistributions under climate change. Such modelling studies, however, often ignore biotic interactions that shape species' geographic ranges. This is especially problematic for coral reefs, which host a high diversity of species and interactions. We tested how biotic interactions affect the distribution patterns of obligate coral‐dwelling Trapezia crabs.LocationGlobal coastal ocean.Time Period2000–2014, 2040–2050, 2090–2100.Major Taxa StudiedCorals and coral‐dwelling Trapezia crabs.MethodsWe determined the symbiotic relationships between 22 crab species in the genus Trapezia and corals via field survey and extensive literature review. We first developed SDMs for coral and crab species using exclusively abiotic variables (abiotic‐only models for corals and crabs). Then we constructed a second set of models where we accounted for coral distributions into crab predictions by combining model predictions for the two taxa a posteriori (abiotic‐plus‐biotic models for crabs only).ResultsWe obtained 30 commonly accepted coral‐crab symbiotic relationships from nine Trapezia crab and six stony coral species. The abiotic‐only model predictions showed that six corals may lose approximately one‐sixth of suitable ranges under RCP 8.5 in 2040–2050. The two types of models for crabs yielded largely different habitat suitability predictions and accounting for biotic interactions into SDM predictions exacerbates the predicted impacts of climate change on coral‐dwelling crabs.Main ConclusionsOur results show large discrepancies in crab spatial distribution patterns with and without accounting for symbiotic interactions. Our findings highlight the important role of modeller's decision on accounting for biotic interactions when predicting the geographical ranges of coral‐dwelling species, with important implications for designing future conservation and management strategies for marine species.

Same places, same stories? Genomics reveals similar structuring and demographic patterns for four Pocillopora coral species in the southwestern Indian Ocean

AbstractAimEfficiently protecting species requires knowing their ecological, life‐history and reproductive traits. This is particularly decisive for scleractinian corals, key components of coral reefs, which are experiencing critical declines. Yet their connectivity remains insufficiently documented. Here, we focused on four distinct species of the coral genus Pocillopora found in diverse habitats of the southwestern Indian Ocean and presenting various reproductive strategies. We aimed to understand whether these traits affect species connectivity.LocationArchipelagos and islands of the southwestern Indian Ocean.TaxonPocillopora spp.MethodsWe used target capture to collect single‐nucleotide polymorphisms (SNPs) from over a thousand colonies sampled across nine localities. From the ca. 1400 SNPs retained per species, Bayesian clustering methods, networks and demographic inferences were applied to first infer the population genetic structure and connectivity of each species, then the demographic history of each population.ResultsAll four Pocillopora species exhibited almost the same genetic structuring pattern, reflecting the sampled ecoregions (Madagascar and surrounding islands vs. Mascarene Islands). However, the genetic differentiation was stronger (FST about 10 times higher) for P. acuta, the species inhabiting more enclosed habitats, such as lagoons and shallow waters, and reproducing mainly asexually. Similarly, all populations, except those from P. acuta, showed a signature of population expansion ca. 100,000 years ago, following the penultimate glacial period.Main ConclusionsThese results indicate reduced gene flow between Madagascar and the Mascarene Islands, probably linked to currents, suggesting distinct connectivity networks that should be considered independently when setting up conservation plans. In addition, shared demographic histories reflect that populations from these species have probably met the same environmental constraints and reacted similarly, something that should be considered in light of the ongoing rapid climate change.

Bleaching threatens positive carbonate budgets on Bahraini reefs

Bleaching events impact coral reef functionality and carbonate budget dynamics, which is reflected in reduced reef framework accretion, hindering reef ability to keep pace with sea-level rise projections. Reefs in the Arabian Gulf exist in harsh environmental conditions with seasonal temperatures ranging between 16 and 36 °C. Despite the high thermal thresholds (~ 35 °C) of corals in this region, extensive bleaching and high coral mortality have been reported regionally in 2017. We quantify reef carbonate budgets at a near shore and an offshore reef site in Bahrain pre-bleaching in May 2017 and post-bleaching in May 2018 to assess the impacts of the 2017 severe bleaching event on the budgetary state. Results indicate an overall decrease in hard coral cover from 14.2 ± 5.5 to 8.5 ± 1.4% and a decline in the net carbonate budget state from 3.6 ± 2.2 to 0.3 ± 0.3 kg CaCO3 m−2 year−1 at the shallow nearshore Fasht Al Adhm reef indicating a shift from a positive budgetary state to net neutral, while the deeper offshore Reef Bul Thamah has increased positively from 3.7 ± 1.2 to 4.2 ± 0.6 kg CaCO3 m−2 year−1. We attribute the decline in the nearshore reef to the bleaching event which took place between July and October 2017, resulting in high coral mortality rates and subsequent reduced framework carbonate production. Predicted warming trends present a threat to the structural integrity of shallow Bahraini reefs, compromising their ability to keep pace with future sea-level rise projections.