Posts Tagged 'Red Sea'

Yemen fisheries and climate change

Published 31 December 2025 Newsletters and reports Closed
Tags: , ,

Yemen’s extensive coastline, encompassing the southern Red Sea, Gulf of Aden, and northwest Arabian Sea, is home to rich marine biodiversity and historically productive fisheries, crucial for the nation’s economy, food security, and livelihoods (Figure 1). However, the intersection of global climate change and a prolonged internal conflict has significantly disrupted marine ecosystems and fisheries management, exacerbating already critical challenges.

This report addresses these pressing issues through two interconnected analyses. The first examines recent climate-driven changes in marine ecosystem health indicators, providing insights into seasonal variability, long-term trends, and impacts from extreme climate events such as Cyclone Tej in 2023. The second analysis investigates the status of Yemen’s fisheries, highlighting historical trends, the impacts of conflict, and gaps in current monitoring and management practices.

Leveraging innovative methodologies, satellite remote sensing, computer vision, and collaborative in situ data collection, the report aims to present a cohesive framework for revitalizing Yemen’s marine research and fisheries management. Ultimately, the findings underscore the urgency of implementing targeted, adaptive, and evidence-based policies to sustain Yemen’s coastal ecosystems and the livelihoods dependent upon them.

The report is structured as follows: Section 1 presents analysis of seasonal variability, climate shocks and extreme events along with longer-term temporal trends on temperature, oceanic biomass and productivity, salinity and ocean acidification in Yemen’s coastal waters; Section 2 presents analysis of the fisheries sector, notably identifying the existing data gaps and the absence of reliable monitoring as a result of the ongoing unrest; based on these analyses, Section 3 proposes a framework for the creation of a dynamic fisheries monitoring and management model; and Section 4 concludes with policy recommendations.

While this study does not include formal projections, observed decadal trends across Yemen’s marine regions allow for indicative interpretation of the likely direction of change in key ecosystem indicators. The table below summarizes historical trajectories (2004 – 2024) of these variables, which may inform expectations of future biological productivity if current drivers persist.

Continue reading ‘Yemen fisheries and climate change’

4D insights into coral biomineralization: effects of ocean acidification on the early skeleton development of a stony coral

Published 24 September 2025 Science Closed
Tags: , , , , ,

Coral biomineralization drives the formation of reef structures, but ocean acidification (OA) threatens this process. Coral survival requires effective skeletogenesis in early life stages, through the formation of co joined growth zones: rapid accretion deposits (RADs) and thickening deposits (TDs). Contrasting theories and lack of data on how these zones form hamper our understanding of normal coral growth and under future OA. This study describes growth patterns of RADs and TDs during the early stages of coral calcification under both normal and OA conditions. The work reveals geometric characteristics of RADs and TDs at micro- and sub-micrometer scales, as a basis for learning how OA impacts the early-formed skeletons. By combining material science approaches and Monte-Carlo simulations to model electron interactions that probe mineral phase composition, we show how TDs and RADs form simultaneously, challenging the classical “step-by-step” growth hypothesis. Unexpectedly, under normal pH, TDs comprise ≈65% amorphous calcium carbonate (ACC) and only 35% crystalline aragonite. Under OA, skeletons exhibit higher densities, with only 50% ACC. RADs are underdeveloped under OA, reducing skeletal bending resistance and increasing fracture risk. These findings reveal that the effect of OA on coral skeletogenesis is more complex than previously understood.

Continue reading ‘4D insights into coral biomineralization: effects of ocean acidification on the early skeleton development of a stony coral’

The impacts of ocean acidification on coral reefs in the Red Sea and ways to address it – a review

Published 17 September 2025 Science Closed
Tags: , , , , , ,

Ocean acidification (OA) is an escalating environmental challenge that poses significant threats to marine ecosystems, especially coral reefs. The Red Sea, characterized by its distinct marine biodiversity and climatic conditions, is becoming increasingly susceptible to the effects of (OA). This review investigates the impact of ocean acidification on coral reefs in the Red Sea, emphasizing physiological, ecological, and socio-economic consequences. Alterations in seawater chemistry, notably a reduction in pH and the availability of carbonate ions, impede coral calcification, disrupt symbiotic relationships, and contribute to coral bleaching. The review also highlights the vulnerability of coral species in the Red Sea, which is further exacerbated by local stressors such as temperature variations, pollution, and overfishing. Additionally, it examines various strategies to mitigate these impacts, including active coral reef restoration, genetic adaptation research, the creation of marine protected areas, and the mitigation of local environmental stressors. Addressing ocean acidification in the Red Sea necessitates a combination of global and regional initiatives aimed at reducing (CO2) emissions, alongside local conservation measures to enhance the resilience of coral reef ecosystems. This review highlights the critical need for interdisciplinary research and cooperative efforts to protect the future of coral reefs in the region.

Continue reading ‘The impacts of ocean acidification on coral reefs in the Red Sea and ways to address it – a review’

pH acidification in the Red Sea: a machine learning-based validation study

Published 19 August 2025 Science Closed
Tags: , , , ,

Highlights

  • Predicting ocean acidification in the Red Sea using advanced machine learning models, providing critical insights for regional marine ecosystem management.
  • Models yielded more efficient and effective results compared to traditional methods
  • Artificial intelligence-based models offer a potential solution for the management of sustainable ecosystems with a focus on environmental sustainability
  • Artificial intelligence-based applications offer significant potential for integration within remote monitoring systems

Abstract

This study presents application and performance comparison of various machine learning (ML) techniques to analyze pH variations in the Red Sea between the years 2021 and 2024, utilizing satellite remote sensing from the Copernicus Programme. The accuracy of the model is enhanced by employing data preprocessing. The performance of a number of machine learning models (Stepwise Linear Regression, Gaussian Process Regression, Linear Regression, Support Vector Machines and Neural Networks) are assessed. The results shown that the highest predictive accuracy is achieved by Stepwise Linear Regression and Linear Regression models. These models found to be superior in predicting pH changes due to seasonal phytoplankton blooms, vertical mixing of waters, and CO₂ infusion from the atmosphere accurately. Therefore, this research proposes a comprehensive approach for evaluating long-term changes in pH levels using robust data, improving strategic environmental governance in marine ecosystems. ML-based algorithms offer more integrated, cost-effective, and scalable solutions for monitoring ocean acidification, outperforming traditional approaches in both efficiency and adaptability.

Continue reading ‘pH acidification in the Red Sea: a machine learning-based validation study’

Macroalgal presence decreases coral calcification rates more than ocean acidification

Published 12 June 2024 Science Closed
Tags: , , , , , , , , , ,

Global coral reef degradation has precipitated phase shifts toward macroalgal-dominated communities. Despite the negative repercussions for reefscapes, higher abundances of primary producers have the potential to positively impact the physicochemical environment and mitigate negative impacts of ocean acidification (OA). In this study, we investigated the influence of macroalgal (cf. Sargassum vulgare) density on coral (Acropora millepora and A. hemprichii) calcification rates under current and future OA conditions. Corals were resistant to OA up to ~ 1100 µatm, with no changes in calcification rates. However, the presence of (low and high density) algae reduced calcification rates by ~ 41.8%, suggesting either a chemical defense response due to algal metabolites or potential physical impacts from shading or abrasion. Documented beneficial buffering effects of macroalgae in OA may also elicit negative impacts on coral calcification, suggesting further work is needed to elucidate how species interactions influence responses to projected climate change.

Continue reading ‘Macroalgal presence decreases coral calcification rates more than ocean acidification’

Hydrographical studies in the nearshore seawaters of the Red Sea coast of Al-Hodeida city, Yemen

Published 30 January 2024 Science Closed
Tags: , ,

Hydrographic studies of nearshore seawaters are important because they are sensitive to both natural and human influences. The hydrographic study is very important for nearshore waters because it is very sensitive to natural and human influences. In this research, an attempt was made to study the hydrographic properties of the nearshore waters of the Red Sea coast of Hodeida city, Yemen. During the period from December 2021 to June 2022, to represent the two seasons of winter and summer. The water temperatures ranged from 30 to 34.5 °C, salinity fluctuated from 39.3 to 42.4 psu, pH varied from 7.9 to 8.2 and dissolved oxygen ranged from 4.88 to 8.54 mg/l. The higher values of temperature and salinity were recorded during summer season. In contrast, an increase in pH and dissolved oxygen were observed during winter season. The present study confirmed that salinity has a negative correlation with pH and dissolved oxygen although it was not significant and also it showed significant positive correlation between pH and dissolved oxygen (0.828). The hydrographical parameters showed significant spatial and temporal variations. The present baseline information is useful for the further ecological monitoring and assessment along the coastal beaches.

Continue reading ‘Hydrographical studies in the nearshore seawaters of the Red Sea coast of Al-Hodeida city, Yemen’

Effects of excess atmospheric CO2 on calcium carbonate producers along the Red Sea coast of Yemen: its risk and socio-economic impacts

Published 23 January 2024 Science Closed
Tags: , ,

The formation of calcite and aragonite, integral components of marine organisms’ skeletons, is contingent on the degree of saturation (W) of seawater with respect to carbonate minerals. The decrease in W, driven by an excess of atmospheric carbon dioxide, poses challenges for calcifying organisms in their ability to create and maintain their skeletal structures and shells. As a result, we conducted a collection of surface seawater samples from various locations along the Red Sea coast of Yemen to address three key objectives: (1) ascertain the current W values for calcite and aragonite, (2) project alterations in these values attributable to seawater pH reduction (acidification) over the next 50 and 200 years, and (3) assess potential ecological consequences and risks associated with these impeding changes.  During both winter and summer, we conducted measurements of various oceanographic parameters, including temperatures (ToC), salinities (S), pH values, and total alkalinities (TA). In winter season, these parameters were ToC = 26.4±0.5oC, S = 36.9±0.5, pH = 8.16±0.3 and TA = 2.409±0.104 meq/Kg, whereas in summer ToC = 34.6±0.6oC, S = 38.5±0.2, pH = 8.11±0.12 and TA = 2.428±0.036 meq/Kg. These measured parameters served as crucial inputs for the assessment of carbonate chemistry, including the determination of seawater’s W values with respect to both calcite and aragonite. The findings indicated that surface seawater was supersaturated with respect to both calcite and aragonite. The percent degree of saturation (%W) for calcite was 553±89% in winter and 607±77% in summer, while for aragonite was 367±58% in winter and 415±53% in summer.  Over the course of the next five decades, the surface seawater %W with respect to calcite is projected to decrease approximately 464±111% during winter months and 499±78% during summer. At the same time, it is expected to decline to around 251±60% in winter and 341±53% in summer for aragonite. In the next two centuries, these percentages are anticipated to further decrease to 249±57% in winter and 281±48% in summer for calcite, and to 135±31% in winter and 192±33% in summer for aragonite. Acidification of seawater will have serious environmental consequences on the marine and coastal habitats of the Red Sea of Yemen and the entire region. Further studies are warranted to monitor and investigate the occurrence, distribution, mineralogy of corals, and the effects of physical and chemical parameter variations on their growth in the region.

Continue reading ‘Effects of excess atmospheric CO2 on calcium carbonate producers along the Red Sea coast of Yemen: its risk and socio-economic impacts’

Inferring the health of coral reefs on the Egyptian coast of the Gulf of Aqaba for three branching-coral species

Published 9 January 2024 Science Closed
Tags: , , , , ,

Abstract

This investigation examined the vulnerability of three branching coral species (Acropora humilis, Pocillopora damicornis, and Stylophora pistillata) to environmental changes within the marine reserves of Taba, Nuweiba, and Dahab in the Gulf of Aqaba. Coral growth rates were assessed as a key indicator of coral reef vitality, reacting to shifting physicochemical parameters. A. humilis manifested the highest growth rate, followed by S. pistillata and P. damicornis. Site-specific data analysis found Dahab displayed the greatest coral proliferation, with Taba exhibiting the least. Accounting for seasonal changes, spring showed maximal coral growth. Statistical analysis revealed a positive correlation between salinity and coral growth rate, contrasted by a negative correlation with variables such as pH, PO4-P, and silicate (SiO4-Si). This work underscores the significant influence of environmental factors on coral growth rates, and by extension, the health of coral reef ecosystems. These findings are integral to coral reef management, suggesting mitigation of adverse environmental factors could enhance these ecosystems’ resilience against climatic shifts and human-induced stressors. By combining species, site, seasonal, and physicochemical variations, this research underlines the importance of localized conservation strategies.

Highlights

  • Robust Reef Health: The paper’s findings reveal a remarkable resilience and overall good health of coral reefs in Egypt’s protected marine environments, even when compared to reefs in more polluted and anthropogenically impacted areas.
  • Effective Protection Measures: The study underscores the importance of the protective measures implemented in these marine preserves, indicating that they have played a crucial role in maintaining the health and status of the intricate and invaluable reef ecosystems.
  • Catalyst for Further Research: The research outcomes provide a strong foundation for future studies aimed at identifying and implementing effective protective measures and adaptive management strategies for coral reefs in diverse ecosystems, with the goal of ensuring their long-term health and preservation.
  • Highlighting Environmental Challenges: The paper emphasizes the relative health of the studied coral reefs despite broader environmental challenges, shedding light on the potential success of conservation efforts within these specific marine regions.
Continue reading ‘Inferring the health of coral reefs on the Egyptian coast of the Gulf of Aqaba for three branching-coral species’

Simulated climate change scenarios impact the reproduction and early life stages of a soft coral

Published 25 November 2020 Science Closed
Tags: , , , , , , , , ,

Highlights

  • A change in the timing of onset of the soft coral breeding event occurred under elevated temperature and reduced pH seawater conditions.
  • A disruption of the synchronicity of the breeding event occurred under elevated temperature and reduced pH seawater conditions.
  • End-of-the-century seawater conditions are expected to affect the reproduction of the soft coral Rhytisma fulvum.
  • Planula survival and polyp metamorphosis rates were significantly reduced under both end-of-the-century seawater conditions compared to propagules reared under ambient conditions.
  • The photosynthetic capacity of the parent soft coral colonies was reduced under the end-of-the-century seawater conditions in comparison to those under the ambient conditions.

Abstract

Coral reefs are threatened worldwide by global climate change, manifested in anthropogenic ocean warming and acidification. Despite the importance of coral sexual reproduction for the continuity of coral reefs, our understanding of the extent of the impact of climate change on coral sexual reproduction, particularly on coral reproductive phenology and early life stages, is limited. Here, we experimentally examined the effects of predicted end-of-the-century seawater conditions on the sexual reproduction and photosynthetic capacity of a Red-Sea zooxanthellate octocoral, Rhytisma fulvum. Sexually mature colonies were exposed to ambient temperature and pH conditions and to Representative Concentration Pathway (RCP) conditions (4.5 and 8.5), five weeks prior to their expected surface-brooding event. The reproductive phenology of the colonies under the simulated seawater conditions was compared to that on the natural reef. In addition, subsequent planulae development and their metamorphosis into primary polyps under the same RCP conditions as their parent colonies were monitored in a running seawater system. The results reveal that both RCP conditions led to a change in the timing of onset of the surface-brooding event and its synchronicity. In contrast, the surface-brooding event under ambient conditions co-occurred with that of the in-situ reef colonies and maintained its synchrony. Similarly, planula survival and polyp metamorphosis rate were significantly reduced under both RCP conditions compared to propagules reared under ambient conditions. In addition, the photosynthetic capacity of the parent colonies under both RCPs showed a reduction relative to that under the ambient conditions in the experiment, suggesting a reduction in carbon fixation during the late stages of gametogenesis. While our findings indicate that octocoral reproductive phenology is affected by environmental changes, further work is required in order to elucidate the long-term implications for the R. fulvum population in the northern Red Sea.

Continue reading ‘Simulated climate change scenarios impact the reproduction and early life stages of a soft coral’

Differential sensitivity of a symbiont‐bearing foraminifer to seawater carbonate chemistry in a decoupled DIC‐pH experiment

Published 28 October 2020 Science Closed
Tags: , , , , , , ,

Larger benthic foraminifera (LBF) are unicellular eukaryotic calcifying organisms and an important component of tropical and subtropical modern and ancient oceanic ecosystems. They are major calcium carbonate producers and important contributors to primary production due to the photosynthetic activity of their symbiotic algae. Studies investigating the response of LBF to seawater carbonate chemistry changes are therefore essential for understanding the impact of climate changes and ocean acidification (OA) on shallow marine ecosystems. In this study, calcification, respiration, and photosynthesis of the widespread diatom‐bearing LBF Operculina ammonoides were measured in laboratory experiments that included manipulation of carbonate chemistry parameters. pH was altered while keeping dissolved inorganic carbon (DIC) constant, and DIC was altered while keeping pH constant. The results show clear vulnerability of O. ammonoides to low pH and CO32− under constant DIC conditions, and no increased photosynthesis or calcification under high DIC concentrations. Our results call into question previous hypotheses, suggesting that mechanisms such as the degree of cellular control on calcification site pH/DIC and/or enhanced symbiont photosynthesis in response to OA may render the hyaline (perforate and calcitic‐radial) LBF to be less responsive to OA than porcelaneous LBF. In addition, manipulating DIC did not affect calcification when pH was close to present seawater levels in a model encompassing the total population size range. In contrast, larger individuals (>1,200 μm, >1 mg) were sensitive to changes in DIC, a phenomenon we attribute to their physiological requirement to concentrate large quantities of DIC for their calcification process.

Continue reading ‘Differential sensitivity of a symbiont‐bearing foraminifer to seawater carbonate chemistry in a decoupled DIC‐pH experiment’

Anomalies in the carbonate system of Red Sea coastal habitats (update)

Published 30 January 2020 Science Closed
Tags: , , , ,

We use observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) to assess the impact of ecosystem metabolic processes on coastal waters of the eastern Red Sea. A simple, single-end-member mixing model is used to account for the influence of mixing with offshore waters and evaporation–precipitation and to model ecosystem-driven perturbations on the carbonate system chemistry of coral reefs, seagrass meadows and mangrove forests. We find that (1) along-shelf changes in TA and DIC exhibit strong linear relationships that are consistent with basin-scale net calcium carbonate precipitation; (2) ecosystem-driven changes in TA and DIC are larger than offshore variations in >70 % of sampled seagrass meadows and mangrove forests, changes which are influenced by a combination of longer water residence times and community metabolic rates; and (3) the sampled mangrove forests show strong and consistent contributions from both organic respiration and other sedimentary processes (carbonate dissolution and secondary redox processes), while seagrass meadows display more variability in the relative contributions of photosynthesis and other sedimentary processes (carbonate precipitation and oxidative processes). The results of this study highlight the importance of resolving the influences of water residence times, mixing and upstream habitats on mediating the carbonate system and coastal air–sea carbon dioxide fluxes over coastal habitats in the Red Sea.

Continue reading ‘Anomalies in the carbonate system of Red Sea coastal habitats (update)’

Responses of symbiotic cnidarians to environmental change

Published 20 December 2019 Science Closed
Tags: , , , , , , ,

As climate change intensifies, the capacity of organisms to adapt to changing environments becomes increasingly relevant. Heat-induced coral bleaching –the breakdown of the symbiotic association between coral hosts and photosynthetic algae of the family Symbiodiniaceae– is rapidly degrading reefs worldwide. Hence, there is a growing interest to study symbioses that can persist in extreme conditions. The Red Sea is such a place, known as one of the hottest seas where healthy coral reef systems thrive. Here (Chapter 1), we tested the potential of symbiont manipulation as means to improve the thermal resilience of the cnidarian holobiont, particularly using heat tolerant symbiont species from the Red Sea. We used clonal lineages of the model system Aiptasia (host and symbiont), originating from different thermal environments to assess how interchanging either partner affected their short- and long-term performance under heat stress. Our findings revealed that symbioses are not only intra-specific but have also adapted to native, local environments, thus potentially limiting the acclimation capacity of symbiotic cnidarians to climate change. As such, infection with more heat resistant species, even if native, might not necessarily improve thermotolerance of the holobiont. We further investigated (Chapter 2) how environment-dependent specificity, in this case elevated temperature, affects the establishment of novel symbioses. That is, if Aiptasia hosts are, despite exhibiting a high degree of partner fidelity, capable of acquiring more thermotolerant symbionts under stress conditions. Thus, we examined the infection dynamics of multi-species symbioses under different thermal environments and assessed their performance to subsequent heat stress. We showed that temperature, more than host identity, plays a critical role in symbiont uptake and overall performance when heatchallenged. Additionally, we found that pre-exposure to high temperature plays a fundamental role in improving the response to thermal stress, yet, this can be heavily influenced by other factors like feeding. Like climate change, ocean acidification is a serious threat to corals. Yet, most research has focused on the host and little is known for the algal partner. Thus, here we studied (Chapter 3) the global transcriptomic response of an endosymbiotic dinoflagellate to long-term seawater acidification stress. Our results revealed that despite observing an enrichment of processes related to photosynthesis and carbon fixation, which might seem beneficial to the symbiont, low pH has a detrimental effect on its photo-physiology. Taken together, this dissertation provides valuable insights into the responses of symbiotic cnidarians to future climate and ocean changes.

Continue reading ‘Responses of symbiotic cnidarians to environmental change’

Ocean acidification impact on the grooved carpet shell clam (Ruditapes decussatus)

Published 9 December 2019 Science Closed
Tags: , , , , , ,

The grooved carpet shell clam (Ruditapes decussatus) is one of the most economically important mollusks inhabiting Mediterranean lagoons and sandy beaches both from fisheries and aquaculture. The present study aims to study the impact of different levels of acidification on this calcifying organism. Juvenile clams (avg. Shell Length, SL= 23.22 ± 0.84 mm) were incubated in CO2 enriched seawater at four different CO2 concentrations [420 ppm (ambient control), 550 ppm, 750 ppm and 1050 ppm] representing projected atmospheric CO2 concentration scenarios for the year 2100 by IPCC. The studied biological parameters showed slight decrease with increasing pCO2. However, differences were not significant. Standard length decreased as pCO2 concentration increased, with a maximum average decrease of (-0.12) recorded at 750 ppm as compared to the control group. Regarding total weight, the decrease was highest (-0.10) in both 550 and 1050 ppm. Moreover, clams kept at 550 ppm showed the lowest condition index (11.40 ± 1.49) and highest mortality rate of 8%. The study of physiological response showed increase in metabolic rate and ammonia excretion in both 550 ppm and the control 420 ppm groups. Algal feed clearance rate decreased with increasing acidification with highest value in the control (420 ppm) group and lowest average value of 3.34 l/h-1 in the extremely high pCO2 (1050 ppm) group. By the end of century, ocean acidification may exert additional stress on the health of R. decussatus and its economic value.

Continue reading ‘Ocean acidification impact on the grooved carpet shell clam (Ruditapes decussatus)’

Characterization of the CO2 System in a coral reef, a seagrass meadow, and a mangrove forest in the central Red Sea

Published 29 November 2019 Science Closed
Tags: , ,

The Red Sea is characterized by its high seawater temperature and salinity, and the resilience of its coastal ecosystems to global warming is of growing interest. This high salinity and temperature might also render the Red Sea a favorable ecosystem for calcification and therefore resistant to ocean acidification. However, there is a lack of survey data on the CO2 system of Red Sea coastal ecosystems. A 1‐year survey of the CO2 system was performed in a seagrass lagoon, a mangrove forest, and a coral reef in the central Red Sea, including fortnight seawater sampling and high‐frequency pHT monitoring. In the coral reef, the CO2 system mean and variability over the measurement period are within the range of other world’s reefs with pHT, dissolved inorganic carbon (DIC), total alkalinity (TA), pCO2, and Ωarag of 8.016±0.077, 2061±58 μmol/kg, 2415±34 μmol/kg, 461±39 μatm, and 3.9±0.4, respectively. Here, comparisons with an offshore site highlight dominance of calcification and photosynthesis in summer‐autumn, and dissolution and heterotrophy in winter‐spring. In the seagrass meadow, the pHT, DIC, TA, pCO2, and Ωarag were 8.00±0.09, 1986±68 μmol/kg, 2352±49 μmol/kg, 411±66 μatm, and 4.0±0.3, respectively. The seagrass meadow TA and DIC were consistently lower than offshore water. The mangrove forest showed the highest amplitudes of variation, with pHT, DIC, TA, pCO2, and Ωarag, were 7.95±0.26, 2069±132 μmol/kg, 2438±91 μmol/kg, 493±178 μatm, and 4.1±0.6, respectively. We highlight the need for more research on sources and sinks of DIC and TA in coastal ecosystems.

Continue reading ‘Characterization of the CO2 System in a coral reef, a seagrass meadow, and a mangrove forest in the central Red Sea’

Environmental and biological controls on Na∕Ca ratios in scleractinian cold-water corals (update)

Published 23 September 2019 Science Closed
Tags: , , , , , , , ,

Here we present a comprehensive attempt to correlate aragonitic Na∕Ca ratios from Desmophyllum pertusum (formerly known as Lophelia pertusa), Madrepora oculata and a caryophylliid cold-water coral (CWC) species with different seawater parameters such as temperature, salinity and pH. Living CWC specimens were collected from 16 different locations and analyzed for their Na∕Ca ratios using solution-based inductively coupled plasma-optical emission spectrometry (ICP-OES) measurements.

The results reveal no apparent correlation with salinity (30.1–40.57 g kg−1) but a significant inverse correlation with temperature (−0.31±0.04 mmolmol−1∘C−1). Other marine aragonitic organisms such as Mytilus edulis (inner aragonitic shell portion) and Porites sp. exhibit similar results highlighting the consistency of the calculated CWC regressions. Corresponding Na∕Mg ratios show a similar temperature sensitivity to Na∕Ca ratios, but the combination of two ratios appears to reduce the impact of vital effects and domain-dependent geochemical variation. The high degree of scatter and elemental heterogeneities between the different skeletal features in both Na∕Ca and Na∕Mg, however, limit the use of these ratios as a proxy and/or make a high number of samples necessary. Additionally, we explore two models to explain the observed temperature sensitivity of Na∕Ca ratios for an open and semi-enclosed calcifying space based on temperature-sensitive Na- and Ca-pumping enzymes and transport proteins that change the composition of the calcifying fluid and consequently the skeletal Na∕Ca ratio.

Continue reading ‘Environmental and biological controls on Na∕Ca ratios in scleractinian cold-water corals (update)’

Anomalies in the carbonate system of Red Sea coastal habitats

Published 4 June 2019 Science Closed
Tags: , , , ,

We use observations of dissolved inorganic carbon (DIC) and total alkalinity (TA) to assess the impact of ecosystem metabolic processes on coastal waters of the eastern Red Sea. A simple, single-end-member mixing model is used to account for the influence of mixing with offshore waters and evaporation/precipitation, and to model ecosystem-driven perturbations on the carbonate system chemistry of coral reefs, seagrass meadows and mangrove forests. We find that (1) along-shelf changes in TA and DIC exhibit strong linear trends that are consistent with basin-scale net calcium carbonate precipitation; (2) ecosystem-driven changes in TA and DIC are larger than offshore variations in > 85 % of sampled seagrass meadows and mangrove forests, changes which are influenced by a combination of longer water residence times and community metabolic rates; and (3) the sampled mangrove forests show strong and consistent contributions from both organic respiration and other sedimentary processes (carbonate dissolution and secondary redox processes), while seagrass meadows display more variability in the relative contributions of photosynthesis and other sedimentary processes (carbonate precipitation and oxidative processes).

Continue reading ‘Anomalies in the carbonate system of Red Sea coastal habitats’

Behavioural responses of fish groups exposed to a predatory threat under elevated CO2

Published 1 May 2019 Science Closed
Tags: , , , , ,

Highlights

• Only a few studies assessed how ocean acidification affects the behaviour of fish in groups.

• Shelter use and group cohesion were assessed with or without a predatory treat at high CO2 levels.

• Fish group behaviour was not affected by elevated CO2 levels in the absence of the predator.

• Fish groups from elevated CO2 were bolder than control ones under a predatory treat.

• When a predator was present, group cohesion increased regardless of CO2 conditions.

Abstract

Most of the studies dealing with the effects of ocean acidification (OA) on fish behaviour tested individuals in isolation, even when the examined species live in shoals in the wild. Here we evaluated the effects of elevated CO2 concentrations (i.e. ∼900 μatm) on the shelter use and group cohesion of the gregarious damselfish Chromis viridis using groups of sub-adults exposed to a predatory threat. Results showed that, under predatory threat, fish reared at elevated CO2 concentrations displayed a risky behaviour (i.e. decreased shelter use), whereas their group cohesion was unaffected. Our findings add on increasing evidence to account for social dynamics in OA experiments, as living in groups may compensate for CO2-induced risky behaviour.

Continue reading ‘Behavioural responses of fish groups exposed to a predatory threat under elevated CO2’

Developmental carryover effects of ocean warming and acidification in corals from a potential climate refugium, the Gulf of Aqaba

Published 23 January 2019 Science Closed
Tags: , , , , , , , ,

Coral reefs are degrading from the effects of anthropogenic activities, including climate change. Under these stressors, their ability to survive depends upon existing phenotypic plasticity, but also transgenerational adaptation. Parental effects are ubiquitous in nature, yet empirical studies of these effects in corals are scarce, particularly in the context of climate change. This study exposed mature colonies of the common reef-building coral Stylophora pistillata from the Gulf of Aqaba to seawater conditions likely to occur just beyond the end of this century during the peak planulae brooding season (Representative Concentration Pathway 8.5: pH −0.4 and +5°C beyond present day). Parent and planulae physiology were assessed at multiple time points during the experimental incubation. After 5 weeks of incubation, the physiology of the parent colonies exhibited limited treatment-induced changes. All significant time-dependent changes in physiology occurred in both ambient and treatment conditions. Planulae were also resistant to future ocean conditions, with protein content, symbiont density, photochemistry, survival and settlement success not significantly different compared with under ambient conditions. High variability in offspring physiology was independent of parental or offspring treatments and indicate the use of a bet-hedging strategy in this population. This study thus demonstrates weak climate-change-associated carryover effects. Furthermore, planulae display temperature and pH resistance similar to those of adult colonies and therefore do not represent a larger future population size bottleneck. The findings add support to the emerging hypothesis that the Gulf of Aqaba may serve as a coral climate change refugium aided by these corals’ inherent broad physiological resistance.

Continue reading ‘Developmental carryover effects of ocean warming and acidification in corals from a potential climate refugium, the Gulf of Aqaba’

Coral reefs of the Red Sea — challenges and potential solutions

Published 14 January 2019 Science Closed
Tags: , , ,

The Red Sea is a unique body of water, hosting some of the most productive and diverse coral reefs. Human populations along coasts of the Red Sea were initially sparse due to the hot and arid climate surrounding it, but this is changing with improved desalination techniques, accessible energy, and increased economic interest in coastal areas. In addition to increasing pressure on reefs from coastal development, global drivers, primarily ocean acidification and seawater warming, are threatening coral reefs of the region. While reefs in southern sections of the Red Sea live near or above their maximum temperature tolerance and have experienced bleaching events in the recent past, coral reefs in northern sections are considered a coral reef refugia from global warming and acidification, at least for the coming decades. Such differential sensitivities along the latitudinal gradient of the Red Sea require differential solutions and management. In an effort to identify the appropriate solutions to conserve and maintain resilience of these reefs along a latitudinal gradient, we used a SWOT analysis (strengths/weaknesses/opportunities/threats) to frame the present situation and to propose policy solutions as useful planning procedures. We highlight the need for immediate action to secure the northern sections of the Red Sea as a coral reef climate change refuge by management and removal of local stressors. There is a need to strengthen the scientific knowledge base for proper management and to encourage regional collaboration on environmental issues. Based on scientific data, solutions such as marine protected areas, fishing regulation, and reef restoration approaches were ranked for five distinct latitudinal sections in the Red Sea and levels of interventions are recommended.

Continue reading ‘Coral reefs of the Red Sea — challenges and potential solutions’

Carbonates dissolution and precipitation in hemipelagic sediments overlaid by supersaturated bottom-waters – Gulf of Aqaba, Red Sea

Published 18 December 2018 Science Closed
Tags: , , ,

Whether CaCO3 dissolves within the top centimeters of marine sediments overlaid by deep, supersaturated bottom waters remains an area of debate in geochemistry. This uncertainty stems from the fact that different methods used to assess CaCO3 dissolution rates often provide what appear to be profoundly different results. Here we combine microelectrode and porewater chemistry profiles, core incubation experiments, mineral characterizations and observations of the state of preservation of coccolithophorid exoskeletons for a holistic view of carbonate reactions within the top 30 centimeters of hemipelagic sediments from the Gulf of Aqaba, Red Sea. Calculations based on pH and O2 microelectrode data suggest that rapid metabolic dissolution of carbonate minerals occurs in these sediments within the top two millimeters. Porewater chemistry supports these calculations. The porewater-based observations are further supported by sedimentological characteristics such as aragonite content, and dissolution pitting and fragmentation of coccoliths in sediment layers deposited over the last 200 y. Dissolution appears to be occurring today within surface sediments despite the bulk porewater solution being supersaturated with respect to aragonite and Mg-calcite. In spite of intense dissolution within the sediments, there is no evidence for significant alkalinity and/or calcium fluxes (transport) into bottom waters. It appears that the supersaturated bottom water promotes the removal of all excess alkalinity and calcium produced within the sediment, by CaCO3 precipitation at or above the sediment/ bottom water interface. The precipitation mechanism may be by either benthic organisms (biogenic precipitation) or inorganically (direct precipitation on settling CaCO3 grains). We suggest that authigenic precipitation of (Ca,Mn)CO3 as it becomes supersaturated below 3 cm in the sediments can reconcile the evidence for carbonate dissolution in what appears to be supersaturated conditions. This means that MnCO3 replaces CaCO3 within the nanofossils below ∼3 cm, and that part of the manganese rich CaCO3 is bioturbated upwards into undersaturated conditions, facilitating dissolution of these fossils. Diminished calcite and aragonite concentrations in sediments deposited in recent decades are proposed to be a result of increased manganese cycling rates and greater rates of coupled dissolution within the interfacial sediments, possibly combined with diminished calcareous plankton productivity, in response to increased surface water primary productivity.

Continue reading ‘Carbonates dissolution and precipitation in hemipelagic sediments overlaid by supersaturated bottom-waters – Gulf of Aqaba, Red Sea’

Subscribe

Search

  • Reset

OA-ICC Highlights

Resources