Coral Reef Sites Research Articles

Protection efforts have resulted in ~10% of existing fish biomass on coral reefs

The amount of ocean protected from fishing and other human impacts has often been used as a metric of conservation progress. However, protection efforts have highly variable outcomes that depend on local conditions, which makes it difficult to quantify what coral reef protection efforts to date have actually achieved at a global scale. Here, we develop a predictive model of how local conditions influence conservation outcomes on ~2,600 coral reef sites across 44 ecoregions, which we used to quantify how much more fish biomass there is on coral reefs compared to a modeled scenario with no protection. Under the assumptions of our model, our study reveals that without existing protection efforts there would be ~10% less fish biomass on coral reefs. Thus, we estimate that coral reef protection efforts have led to approximately 1 in every 10 kg of existing fish biomass.

Development and validation of an experimental life support system to study coral reef microbial communities

In the present study, we developed and validated an experimental life support system (ELSS) designed to investigate coral reef associated bacterial communities. The microcosms in the ELSS consisted of coral reef sediment, synthetic seawater, and specimens of five benthic reef species. These included two hard corals Montipora digitata and Montipora capricornis, a soft coral Sarcophyton glaucum, a zoanthid Zoanthus sp., and a sponge Chondrilla sp.. Physicochemical parameters and bacterial communities in the ELSS were similar to those observed at shallow coral reef sites. Sediment bacterial evenness and higher taxonomic composition were more similar to natural-type communities at days 29 and 34 than at day 8 after transfer to the microcosms, suggesting microbial stabilization after an initial recovery period. Biotopes were compositionally distinct but shared a number of ASVs. At day 34, sediment specific ASVs were found in hosts and visa versa. Transplantation significantly altered the bacterial community composition of M. digitata and Chondrilla sp., suggesting microbial adaptation to altered environmental conditions. Altogether, our results support the suitability of the ELSS developed in this study as a model system to investigate coral reef associated bacterial communities using multi-factorial experiments.

In situ observation of external surface brooding by Clavularia cf. inflata (Octocorallia) on reefs of northwestern Okinawa Island, Japan

ABSTRACT The timing of larval production and release of organisms is important in understanding their presence and prevalence in the environment. On the subtropical coral reefs around Okinawa Island, Japan, the reproductive timing of many soft coral species is still largely unknown. In this study, we report the first documentation of in situ external brooding and planulae release of a stoloniferan octocoral observed on the coral reefs of Okinawa Island. We observe external brooding of embryos and developing larvae on the colony surface and the subsequent planulation of some azooxanthellate larvae of Clavularia cf. inflata from two coral reef sites in the northwestern region of Okinawa Island. These observations indicate that this species reproduces concurrently with other zooxanthellate coral reef anthozoans in the summer season.

Diversity, composition and potential roles of sedimentary microbial communities in different coastal substrates around subtropical Okinawa Island, Japan

BackgroundMarine benthic prokaryotic communities play crucial roles in material recycling within coastal environments, including coral reefs. Coastal sedimentary microbiomes are particularly important as potential reservoirs of symbiotic, beneficial, and pathogenic bacteria in coral reef environments, and therefore presumably play a core role in local ecosystem functioning. However, there is a lack of studies comparing different environments with multiple sites on the island scale, particularly studies focusing on prokaryotic communities, as previous investigations have focused mainly on a single site or on specific environmental conditions. In our study, we collected coastal sediments from seven sites around Okinawa Island, Japan, including three different benthic types; sandy bottoms, seagrass meadows, and hard substratum with living scleractinian corals. We then used metabarcoding to identify prokaryotic compositions and estimate enzymes encoded by genes to infer their functions.ResultsThe results showed that the three substrata had significantly different prokaryotic compositions. Seagrass meadow sites exhibited significantly higher prokaryotic alpha-diversity compared to sandy bottom sites. ANCOM analysis revealed that multiple bacterial orders were differentially abundant within each substratum. At coral reef sites, putative disease- and thermal stress-related opportunistic bacteria such as Rhodobacterales, Verrucomicrobiales, and Cytophagales were comparatively abundant, while seagrass meadow sites abundantly harbored Desulfobacterales, Steroidobacterales and Chromatiales, which are common bacterial orders in seagrass meadows. According to our gene-coded enzyme analyses the numbers of differentially abundant enzymes were highest in coral reef sites. Notably, superoxide dismutase, an important enzyme for anti-oxidative stress in coral tissue, was abundant at coral sites. Our results provide a list of prokaryotes to look into in each substrate, and further emphasize the importance of considering the microbiome, especially when focusing on environmental conservation.ConclusionOur findings prove that prokaryotic metabarcoding is capable of capturing compositional differences and the diversity of microbial communities in three different environments. Furthermore, several taxa were suggested to be differentially more abundant in specific environments, and gene-coded enzymic compositions also showed possible differences in ecological functions. Further study, in combination with field observations and temporal sampling, is key to achieving a better understanding of the interactions between the local microbiome and the surrounding benthic community.

Feeding biology of crown-of-thorns seastars across sites differing in Acropora availability

Crown-of-thorns seastars (COTS, Acanthaster spp.) are a major contributor to coral mortality across the Indo-Pacific and can cause extensive reef degradation. The diet preferences of COTS can influence coral community structure by predation on fast-growing genera such as Acropora and avoidance of rare coral genera. In non-outbreaking populations, this preference can increase species diversity. The feeding biology of Acanthaster cf. solaris was compared at two sites (Shark Alley and Second Lagoon) on One Tree Island reef, located in the southern Great Barrier Reef, to determine whether the availability of Acropora influences differences in COTS movement, feeding preference and feeding rates within the same reef system. Acanthaster cf. solaris were tracked daily for five days across both sites, with measurements of movement, feeding scars and coral composition recorded over this time. While Shark Alley and Second Lagoon have similar live coral cover (40 and 44 % respectively), Shark Alley has significantly lower Acropora availability than Second Lagoon (2 vs 32 %). The feeding rate of COTS was significantly different between Shark Alley and Second Lagoon (259.8 and 733.8 cm2 of coral per day, respectively), but did not differ between seastar size (25–40 cm and >40 cm). Acanthaster cf. solaris showed preference for Pocillopora, Seriatopora, Acropora and Isopora and an avoidance of Porites at both sites. The results suggest that for coral reef sites where Acropora is not dominant, COTS outbreaks may be less likely to initiate, with comparatively low feeding rates found in comparison to coral reefs where Acropora is dominant.

Global patterns and drivers of fish reproductive potential on coral reefs

Fish fecundity scales hyperallometrically with body mass, meaning larger females produce disproportionately more eggs than smaller ones. We explore this relationship beyond the species-level to estimate the “reproductive potential” of 1633 coral reef sites distributed globally. We find that, at the site-level, reproductive potential scales hyperallometrically with assemblage biomass, but with a smaller median exponent than at the species-level. Across all families, modelled reproductive potential is greater in fully protected sites versus fished sites. This difference is most pronounced for the important fisheries family, Serranidae. When comparing a scenario where 30% of sites are randomly fully protected to a current protection scenario, we estimate an increase in the reproductive potential of all families, and particularly for Serranidae. Such results point to the possible ecological benefits of the 30 × 30 global conservation target and showcase management options to promote the sustainability of population replenishment.

Remote submerged banks and mesophotic ecosystems can provide key habitat for endangered marine megafauna.

The importance of some ecosystems remains poorly understood. We showed that mesophotic ecosystems (30 to 150 m) are a key habitat for a critically endangered species, with strong evidence that a globally important population of adult hawksbill turtles (Eretmochelys imbricata) almost exclusively foraged at these depths on remote submerged banks. This discovery highlights the need for such areas to be included in conservation planning, for example, as part of the United Nations High Seas Treaty. We equipped nesting turtles with Fastloc-GPS (Global Positioning System) satellite tags at an Indian Ocean breeding area and they all traveled to deep foraging sites (6765 days of tracking data across 22 individuals including 183,921 dive-depth measurements) rather than shallow coral reef sites. Both chart depths and depth data relayed from the tags indicated that turtles foraged at mesophotic depths, the modal dive depths being between 35 and 40 m. We calculate that 55,554 km2 of the western Indian Ocean alone consists of submerged banks between 30 and 60 m.

Bayesian multi-proxy reconstruction of early Eocene latitudinal temperature gradients

Abstract. Accurately reconstructing large-scale palaeoclimatic patterns from sparse local records is critical for understanding the evolution of Earth's climate. Particular challenges arise from the patchiness, uneven spatial distribution, and disparate nature of palaeoclimatic proxy records. Geochemical data typically provide temperature estimates via transfer functions derived from experiments. Similarly, transfer functions based on the climatic requirements of modern taxa exist for some fossil groups, such as pollen assemblages. In contrast, most ecological and lithological data (e.g. coral reefs and evaporites) only convey information on broad climatic requirements. Historically, most large-scale proxy-based reconstructions have used either geochemical or ecological data, but few studies have combined multiple proxy types into a single quantitative reconstruction. Large spatial gaps in existing proxy records have often been bridged by simple averaging, without taking into account the spatial distribution of samples, leading to biased temperature reconstructions. Here, we present a Bayesian hierarchical model to integrate ecological data with established geochemical proxies into a unified quantitative framework, bridging gaps in the latitudinal coverage of proxy data. We apply this approach to the early Eocene climatic optimum (EECO), the interval with the warmest sustained temperatures of the Cenozoic. Assuming the conservation of thermal tolerances of modern coral reefs and mangrove taxa, we establish broad sea surface temperature ranges for EECO coral reef and mangrove sites. We integrate these temperature estimates with the EECO geochemical shallow marine proxy record to model the latitudinal sea surface temperature gradient and global average temperatures of the EECO. Our results confirm the presence of a flattened latitudinal temperature gradient and unusually high polar temperatures during the EECO, which is supported by high-latitude ecological data. We show that integrating multiple types of proxy data, and adequate prior information, has the potential to enhance quantitative palaeoclimatic reconstructions, improving temperature estimates from datasets with limited spatial sampling.

The microbial community of coral reefs: biofilm composition on artificial substrates under different environmental conditions

Artificial reefs are used as tools for the restoration of degrading coral reefs by providing new settlement substrates. The initial recruitment process consists of the formation of microbial biofilms shortly after deployment. The aim of the present study is to compare biofilm composition and development on artificial substrates at two different coral-reef sites. These locations differ in their environmental conditions, including their level of anthropogenic impact. Substrate and seawater samples were collected four times during the first 6 months after deployment, using a new methodology termed ‘tab-by-tab’. DNA was extracted, sequenced, and sorted for both prokaryotic (16s) and eukaryotic (18s) genes. No difference was found between the planktonic communities in the water, yet significant differences were observed in the biofilm communities on the structures at the two sites. Moreover, differences were recorded in coral recruitment rates, which are known to be affected by biofilm composition. Our findings suggest a potential role of environmental conditions in the early biofilm stages (first few months), which in turn may impact the succession and development of coral-reef communities and the success of artificial reefs as restoration tools.

Environmental DNA captures diurnal fluctuations of surface eukaryotes on a tropical coral reef

AbstractEnvironmental DNA (eDNA) metabarcoding has been widely employed to describe biological communities in the marine environment and to compare the richness and diversity of sites across large spatial scales. However, fine‐scale temporal eDNA dynamics are poorly understood and the time of eDNA sample collection is rarely reported in publications. Here, we collected surface eDNA samples every 6 h, for 3 days, at two coral reef sites to assess fine‐scale changes in the eukaryotic communities detected. Distinct eukaryotic communities were detected at two sites within the same lagoon. Sampling time was found to have a significant effect on ESV and class richness, both peaking during the 1 p.m. sampling time at both sites. Sampling time also had a significant effect on the detection of eukaryotic taxa, with relative read frequency showing clear diurnal patterns in line with the migratory behavior of planktonic groups. Other groups of organisms showed considerable variation in read frequency, highlighting the dynamic nature of marine eukaryotic communities and potential stochasticity of eDNA detections. For eukaryotic communities, eDNA samples can provide a “snapshot” of contemporary biodiversity and provide information on short‐term community dynamics on hyperdiverse coral reefs. However, our findings add to growing evidence that sampling time should be clearly considered and reported in marine eDNA studies and that multiple samples from the same site are needed to facilitate more robust comparisons across sites.

Assessing the ecological risk of heavy metal sediment contamination from Port Everglades Florida USA.

Port sediments are often contaminated with metals and organic compounds from anthropogenic sources. Remobilization of sediment during a planned expansion of Port Everglades near Fort Lauderdale, Florida (USA) has the potential to harm adjacent benthic communities, including coral reefs. Twelve sediment cores were collected from four Port Everglades sites and a control site; surface sediment was collected at two nearby coral reef sites. Sediment cores, sampled every 5 cm, were analyzed for 14 heavy metals using inductively coupled plasma-mass spectrometry. Results for all three locations yielded concentration ranges (µg/g): As (0.607-223), Cd (n/d-0.916), Cr (0.155-56.8), Co (0.0238-7.40), Cu (0.004-215), Pb (0.0169-73.8), Mn (1.61-204), Hg (n/d-0.736), Mn (1.61-204), Ni (0.232-29.3), Se (n/d-4.79), Sn (n/d-140), V (0.160-176), and Zn (0.112-603), where n/d = non-detected. The geo-accumulation index shows moderate-to-strong contamination of As and Mo in port sediments, and potential ecological risk indicates moderate-to-significantly high overall metal contamination. All four port sites have sediment core subsamples with As concentrations above both threshold effect level (TEL, 7.24 µg/g) and probable effect level (PEL, 41.6 µg/g), while Mo geometric mean concentrations exceed the background continental crust level (1.5 µg/g) threshold. Control site sediments exceed TEL for As, while the reef sites has low to no overall heavy metal contamination. Results of this study indicate there is a moderate to high overall ecological risk from remobilized sediment due to metal contamination. Due to an imminent dredging at Port Everglades, this could have the potential to harm the threatened adjacent coral communities and surrounding protected habitats.

Gut content metabarcoding of specialized feeders is not a replacement for environmental DNA assays of seawater in reef environments.

In tropical marine ecosystems, the coral-based diet of benthic-feeding reef fishes provides a window into the composition and health of coral reefs. In this study, for the first time, we compare multi-assay metabarcoding sequences of environmental DNA (eDNA) isolated from seawater and partially digested gut items from an obligate corallivore butterflyfish (Chaetodon lunulatus) resident to coral reef sites in the South China Sea. We specifically tested the proportional and statistical overlap of the different approaches (seawater vs gut content metabarcoding) in characterizing eukaryotic community composition on coral reefs. Based on 18S and ITS2 sequence data, which differed in their taxonomic sensitivity, we found that gut content detections were only partially representative of the eukaryotic communities detected in the seawater based on low levels of taxonomic overlap (3 to 21%) and significant differences between the sampling approaches. Overall, our results indicate that dietary metabarcoding of specialized feeders can be complimentary to, but is no replacement for, more comprehensive environmental DNA assays of reef environments that might include the processing of different substrates (seawater, sediment, plankton) or traditional observational surveys. These molecular assays, in tandem, might be best suited to highly productive but cryptic oceanic environments (kelp forests, seagrass meadows) that contain an abundance of organisms that are often small, epiphytic, symbiotic, or cryptic.

A decade of study on the condition of western Cuban coral reefs, with low human impact.

The long-time study of coral reefs with low human impacts can provide information on the effects of regional pressures like climate change, and is an opportunity to document how these pressures are reflected in coral communities. An example of minimal local anthropogenic impacts are the Guanahacabibes coral reefs, located in the westernmost region of Cuba. The objectives of this study were: to evaluate the temporal variability of six benthic biological indicators of coral reefs, and to explore the possible relationship between predictive abiotic variables and biological response variables. Four coral reef sites were sampled between 2008 and 2017, to analyze biological indicators (living coral cover, fleshy algae index, coral species richness, coral species abundance, coral trait groups species abundance, Functional Reef Index). Seven abiotic variables (wave exposure, sea surface temperature, degree heating week, chlorophyll-a concentration, particulate organic carbon, photosynthetically available radiation, and the diffuse attenuation coefficient) were compiled between 2007 and 2016, from remote sensing datasets, to analyze their relationship with the biological indicators. Permanova statistical analysis was used to evaluate trends in biological variables between sites and years, and Routine Analysis Based on Linear Distances (DISTLM) was used to explore some dependencies between biotic and abiotic variables. We found significant variability in the temporal analysis, with a decrease in living coral cover, a decline in the predominance of the branching and massive framework reef-building species, a decline in Orbicella species abundance, and an increase in the fleshy algae index. Some abiotic variables (average of degree heating weeks, standard deviation of the diffuse attenuation coefficient, average of the sea surface temperature, among others) significantly explained the variability of biological indicators; however, determination coefficients were low. Certain decrease in the functionality of the coral reef was appreciated, taking into account the predominance of secondary and nom-massive framework reef-building species in the last years. A weak association between abiotic and biological variables was found in the temporal analysis. The current scenario of the condition of the coral reefs seems to be regulated by the global effects of climate change, weakly associated effects, and in longer terms.

Coral assemblage structure and condition of the San Felipe Keys National Park, Cuba

Coral reefs provide ecosystem services to humans, essential to protection through different conservation strategies. However, planning and implementing marine conservation management actions must be based on the best available science. Information gaps have resulted in limited knowledge of conservation priorities and a weak conflict resolution and decision-making capacity. The San Felipe Keys National Park (SFKNP), located in the southwestern region of Cuba, is an understudied area with 40 km long forereefs, providing services mainly associated with fisheries (lobster and finfish). This work analyzed the hermatypic coral assemblage structure and condition within the SFKNP and the influence of geographic and environmental factors in its variation. Using stereo videos, we assessed nine coral reef sites between 2013 and 2015, generating 597 transects, in which 10341 colonies, 46 species, and 17 functional entities were found. The dominant species (Siderastrea siderea, Porites astreoides, Agaricia agaricites, and Orbicella faveolata) are mainly massive species with higher depth range, and that visibility in the bottom and habitat heterogeneity explained 57% of coral assemblages’ variation. Besides, the percentage of living coral cover (10%–15%), the prevalence of small-sized colonies (22 cm average), and the high incidence of recent mortality (2%–8% of colonies) indicate the presence of environmental stressors in the SFKNP, such as water turbidity, generated by the natural runoff from the Gulf of Batabanó. These results highlight the importance of enhancing the awareness of the competent authorities and promoting integrated management of the entire western region of the Gulf of Batabanó.

Trends in Dominican Republic Coral Reef Biodiversity 2015–2022

In 2015, we initiated a country-wide coral reef ecosystem-monitoring program in the Dominican Republic (DR) to establish biodiversity baselines against which trends in the most important components of coral reef ecosystem’s structure and function could be tracked. Replicate transects were set at a 10 m depth at each of the 12 coral reef sites within 6 DR regions in 2015, 2017, 2019, and 2022. We quantified the species-level abundances of adult and juvenile corals, reef fishes, sea urchins, lionfishes, and algal functional groups. Country-wide, coral cover and reef fishes have declined. The steepest declines occurred for reefs that had been among the best in the Caribbean in 2015. However, by 2022, adult and juvenile coral, parrotfish, and other herbivores had declined, and macroalgae had increased. The declines in north-shore coral abundance corresponded with the observed disturbances from coral bleaching, hurricanes, and disease. The capacity of reefs to recover from such disturbances has been compromised by abundant and increasing macroalgae that have likely contributed to north-shore declines in juvenile corals. Country-wide, the abundance of all reef fish species has declined below those of other regions of the Caribbean. Improved management of fishing pressure on coral reefs would likely yield positive results.

Quantifying the fragility of coral reefs to hurricane impacts: a case study of the Florida Keys and Puerto Rico

Ecosystems like coral reefs mitigate rising coastal flood risks, but investments into their conservation remain low relative to the investments into engineered risk-mitigation structures. One reason is that quantifying the risk-reduction benefits of coral reefs requires an estimate of their fragility to severe stresses. Engineered structures typically have associated fragility functions which predict the probability of exceeding a damage state with the increasing loading intensity imposed by a stressor, like a hurricane. Here, we propose a preliminary framework for capturing the fragility of coral reefs towards hurricanes in an analogous way to that of an engineered structure. We base our framework on Disturbance Response Monitoring data collected in the Florida Keys and Puerto Rico following hurricanes Irma and Maria. We first establish a qualitatively consistent correlation between hurricane impacts and coral mortality rates using two surveys of coral health. We focus specifically on stony coral mortality as a metric for reef damage, simplifying the effect of coral morphology into a single quantitative index at the site scale. To quantify the loading intensity of a hurricane, we propose a Hurricane Wind Exposure Time that captures spatial variations in the exposure of different coral reef sites to hurricane force winds. We ultimately derive a simple empirical fragility function for the Florida Keys and Puerto Rico to support side-by-side comparisons of the cost-effectiveness of a coral reef and engineered solutions to flood risk reduction in these regions.

Intake of trace contaminants by corals in Abrolhos reef bank (western South Atlantic) during two decades of coastal impacts

Abrolhos is the largest and most diverse coral reef system in the South Atlantic. It is home to several endemic coral species and a site of cetaceous reproduction. Like any other reef ecosystem worldwide, it experiences multiple disturbances associated with increasing sea surface temperatures, El Niño events, and, most recently, oil spill pollution. In addition to these global stressors, the Abrolhos region may have been impacted by coastal human interventions, a large-scale mining disaster, floods, and extra-tropical cyclones that affected the region during the last 20 years. Among these stressors, the Fundão dam collapse (the largest in the Southern Hemisphere) deserves special attention since it delivered significant amounts of iron tailings to the nearby coast. To investigate the region's recent history, we collected, dated, and performed detailed geochemical and isotopic analyses on two coral colonies (i.e., Siderastrea stellata and Mussismilia harttii), in order to determine if effects of recent human activity on reef systems (and most recent natural impacts) could be detected thorough bioaccumulation of metals in their skeletons. In this context, we detected an abrupt increase in Fe and Mn concentrations in the coral skeleton, which are among the main constituents of the Fundão dam tailings. We show that a concomitant increase in metal concentrations tracks contaminant dispersion of the Fundão dam tailings released to the western South Atlantic. Besides this event, our data also show that coastal dredging activities in the nearby coral reef site (i.e., at the Tomba channel) and two natural episodes (i.e., the flood of 2013 and the anomalous extra-tropical cyclonic activity in 2008) were also recorded in the coral skeleton based on changes in Rare Earth Elements distribution, Rb and U concentrations.

A metagenomic-based study of two sites from the Barbadian reef system

We study the microbiome of sea water collected from two locations of the Barbadian coral reefs. The two sites differ in several environmental and ecological variables including their endogenous benthic community and their proximity to urban development and runoffs from inland watersheds. The composition of the microbial communities was estimated using whole genome DNA shotgun sequencing with adjuvant measurements of chemical and environmental qualities. Although both sites exhibit a similar degree of richness, the less urbanized site (Maycocks reef at Hangman’s Bay) has a strong concentration of phototrophs whereas the more urbanized location (Bellairs reef at Folkstone) is enriched for copiotrophs, macroalgal symbionts and marine-related disease-bearing organisms from taxa scattered across the tree of life. Our results are concordant with previous profiles of warm ocean surface waters, suggesting our approach captures the state of each coral reef site, setting the stage for longitudinal studies of marine microbiome dynamics in Barbados.

Temporal functional changes in coral and fish communities on subtropical coastal coral reefs

Context Global and local stressors can drive phase shifts from zooxanthellate scleractinian coral communities to macroalgae-dominated ecosystems. However, our understanding of altered ecosystem functioning, productivity and stability remains limited as pre-shift data are typically lacking for degraded coral-reef sites. Aims Here, we assessed functional changes in fish communities in Nakagusuku Bay, Okinawa, Japan, over 45 years, by comparing pre-disturbance (1975) to post-disturbance (2018–2020) datasets, and identified possible drivers of changes. Methods We analysed data for 393 fish species and 26 coral genera at 13 sites, measured at four-time points (1975, 2018, 2019 and 2020). Analyses were performed using a range of ordination techniques. Key results We found reductions in functional richness and trait space contraction over time for fishes. Changes in coral functional groups over time correlated with changes in the functional diversity of reef-fish communities; a reduction in branching corals reduced habitat availability for coral-reliant fishes. Conclusions Increasing sedimentation and eutrophication as a result of construction along the Nakagusuku Bay coast likely reduced living coral cover and fish diversity, and thermal stress likely facilitated the simplification and shifts of both coral communities and coral specialist fishes away from shore. Implications Both global and local threats need to be considered when assessing functioning of coral-reef ecosystems for coral-reef conservation efforts.

Higher Nighttime Rates of CaCO3 Dissolution in the Nature Reserve Reef, Eilat, Israel in 2015–2016 Compared to 2000–2002

AbstractThe current study (2015–2016) evaluated changes in the net community calcification (NCC) and maximum nighttime CaCO3 dissolution (Dmax) in the Nature Reserve Reef (NRR), northern Gulf of Eilat (GOE), and northern Red Sea, compared to measurements made at the same site during 2000–2002. The NCC and Dmax were calculated as a function of the reef‐water residence time, the difference between the open‐sea total alkalinity (TA) and its reef‐water daily average (for NCC), and its nighttime maximum (for Dmax). The average NCC was 50 ± 13 and 68 ± 22 mmol C m−2 day−1 in 2000–2002 and 2015–2016, respectively. This change is consistent with the live coral cover increase in the NRR during this period, following the final removal of fish cages from the northern GOE in 2008. In contrast, wintertime Dmax values in 2015–2016 were five times higher on average compared to 2000–2002. We hypothesize that these higher rates could be the result of increased boring organism activity and sedimentary organic content, which developed throughout the fish farming period and are maintained by the naturally occurring seasonal eutrophication in the northern GOE. Where, in general, Dmax was higher during the winters, when nighttime reef water aragonite saturation (Ωarag) was lower, while open water chlorophyll a and nitrate were higher, compared to summertime. Thus, it is possible that the combination of seasonal eutrophication and ocean acidification (OA) in the GOE and possibly other coral reef sites around the world, may shift coral reefs to net dissolution even sooner than previously predicted from OA alone.