Posts Tagged 'Red Sea'

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

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

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)

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±0.04mmolmol1C1). 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

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).

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


• 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.


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

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

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’

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Ocean acidification in the IPCC AR5 WG II

OUP book