Posts Tagged 'Red Sea'

Reproductive and trans-generational effect of ocean acidification and warming on the coral Stylophora pistillata in the Gulf of Aqaba

Global warming is threatening 75 % of the world’s coral reefs. The reproduction of corals is a driver for the development of the whole reef ecosystem. Then, it is essential to better understand the transgenerational mechanisms in the response of parents and offspring to elevated temperature and lowered pH. Colonies of Stylophora pistillata from the Gulf of Aqaba during their reproduction period were exposed to a 4°C increase in temperature and a pH of 7.6 for 36 days, then a 6°C increase for six days. Planulae were counted on seven consecutive nights, two times during the experiment period. Physiological characteristics of adult and planulae were assessed on four and five sampling points respectively, as well as the behaviour of the planulae through their incubation. Results show no effect of OWA on the reproduction, parents, and planulae physiology. They suggest that the natural resistance of corals in the Gulf of Aqaba is transmitted from parent to offspring. Data on planulae quantity, survival, settlement, and metabolism provides additional and useful information to understand the biology of this coral, specially in its early-life stage. This study’s outcome is adding evidences of the future development of corals reefs in this region, unlike several other tropical reefs in the world.

Continue reading ‘Reproductive and trans-generational effect of ocean acidification and warming on the coral Stylophora pistillata in the Gulf of Aqaba’

Common reef-building coral in the Northern Red Sea resistant to elevated temperature and acidification

Coral reefs are currently experiencing substantial ecological impoverishment as a result of anthropogenic stressors, and the majority of reefs are facing immediate risk. Increasing ocean surface temperatures induce frequent coral mass bleaching events—the breakdown of the nutritional photo-symbiosis with intracellular algae (genus: Symbiodinium). Here, we report that Stylophora pistillata from a highly diverse reef in the Gulf of Aqaba showed no signs of bleaching despite spending 1.5 months at 1–2°C above their long-term summer maximum (amounting to 11 degree heating weeks) and a seawater pH of 7.8. Instead, their symbiotic dinoflagellates exhibited improved photochemistry, higher pigmentation and a doubling in net oxygen production, leading to a 51% increase in primary productivity. Nanoscale secondary ion mass spectrometry imaging revealed subtle cellular-level shifts in carbon and nitrogen metabolism under elevated temperatures, but overall host and symbiont biomass proxies were not significantly affected. Now living well below their thermal threshold in the Gulf of Aqaba, these corals have been evolutionarily selected for heat tolerance during their migration through the warm Southern Red Sea after the last ice age. This may allow them to withstand future warming for a longer period of time, provided that successful environmental conservation measures are enacted across national boundaries in the region.

Continue reading ‘Common reef-building coral in the Northern Red Sea resistant to elevated temperature and acidification’

Mediterranean versus Red sea corals facing climate change, a transcriptome analysis

The anthropogenic increase in atmospheric CO2 that drives global warming and ocean acidification raises serious concerns regarding the future of corals, the main carbonate biomineralizers. Here we used transcriptome analysis to study the effect of long-term gradual temperature increase (annual rate), combined with lowered pH values, on a sub-tropical Red Sea coral, Stylophora pistillata, and on a temperate Mediterranean symbiotic coral Balanophyllia europaea. The gene expression profiles revealed a strong effect of both temperature increase and pH decrease implying for synergism response. The temperate coral, exposed to a twice as high range of seasonal temperature fluctuations than the Red Sea species, faced stress more effectively. The compensatory strategy for coping apparently involves deviating cellular resources into a massive up-regulation of genes in general, and specifically of genes involved in the generation of metabolic energy. Our results imply that sub-lethal, prolonged exposure to stress can stimulate evolutionary increase in stress resilience.

Continue reading ‘Mediterranean versus Red sea corals facing climate change, a transcriptome analysis’

Spatial competition dynamics between reef corals under ocean acidification

Climate change, including ocean acidification (OA), represents a major threat to coral-reef ecosystems. Although previous experiments have shown that OA can negatively affect the fitness of reef corals, these have not included the long-term effects of competition for space on coral growth rates. Our multispecies year-long study subjected reef-building corals from the Gulf of Aqaba (Red Sea) to competitive interactions under present-day ocean pH (pH 8.1) and predicted end-of-century ocean pH (pH 7.6). Results showed coral growth is significantly impeded by OA under intraspecific competition for five out of six study species. Reduced growth from OA, however, is negligible when growth is already suppressed in the presence of interspecific competition. Using a spatial competition model, our analysis indicates shifts in the competitive hierarchy and a decrease in overall coral cover under lowered pH. Collectively, our case study demonstrates how modified competitive performance under increasing OA will in all likelihood change the composition, structure and functionality of reef coral communities.

Continue reading ‘Spatial competition dynamics between reef corals under ocean acidification’

Environmental controls on daytime net community calcification on a Red Sea reef flat

Coral growth and carbonate accumulation form the foundation of the coral reef ecosystem. Changes in environmental conditions due to coastal development, climate change, and ocean acidification may pose a threat to net carbonate production in the near future. Controlled laboratory studies demonstrate that calcification by corals and coralline algae is sensitive to changes in aragonite saturation state (Ωa), as well as temperature, light, and nutrition. Studies also show that the dissolution rate of carbonate substrates is impacted by changes in carbonate chemistry. The sensitivity of coral reefs to these parameters must be confirmed and quantified in the natural environment in order to predict how coral reefs will respond to local and global changes, particularly ocean acidification. We estimated the daytime hourly net community metabolic rates, both net community calcification (NCC) and net community productivity (NCP), at Sheltered Reef, an offshore platform reef in the central Red Sea. Average NCC was 8 ± 3 mmol m−2 h−1 in December 2010 and 11 ± 1 mmol m−2 h−1 in May 2011, and NCP was 21 ± 7 mmol m−2 h−1 in December 2010 and 44 ± 4 mmol m−2 h−1 in May 2011. We also monitored a suite of physical and chemical properties to help relate the rates at Sheltered Reef to published rates from other sites. While previous research shows that short-term field studies investigating the NCC–Ωa relationship have differing results due to confounding factors, it is important to continue estimating NCC in different places, seasons, and years, in order to monitor changes in NCC versus Ω in space and time, and to ultimately resolve a broader understanding of this relationship.

Continue reading ‘Environmental controls on daytime net community calcification on a Red Sea reef flat’

Ocean acidification in the Arabian Sea and the Red Sea – factors controlling pH

The CO2 increase in the ocean due to uptake of anthropogenic CO2 and the companying lowering of ocean pH is of major concern. In this study we investigated the variability of CO2 system parameters, focusing particularly on the pH and how it changes with changes in other parameters like: temperature (T), salinity (S), total dissolved inorganic carbon (CT ), and total alkalinity (AT). For Arabian Sea the data from the United States Joint Global Ocean Flux Study (US{JGOFS) in 1995 were used. For the Red Sea data from the Geochemical Ocean Section Study (GEOSECS) in 1977 and the Mer Rouge (MEROU) cruises in June and October 1982 were used.

The seasonal and spatial variations in pH and therefore also for calcium carbonate saturation (Ar for aragonite and Ca for calcite) are controlled by biological and physical processes that in turn are driven by the in uence of monsoonal seasons. In winter season the surface average pH, Ar, and Ca in the Arabian Sea were 8.070.01, 3.90.1 and 5.90.2, respectively. A relatively high biological
production, due to the winter cooling and mixing caused by the northeast monsoonal winds increases the pH. During summer season, Southwestern monsoonal winds caused upwelling along the coast of Oman, resulting in extremely low pH values (7.9) and lower saturation for aragonite (Ar 2.36) and for calcite (Ca 3.62). Because of the strong change in pH, this area might serve as a natural laboratory for studies of ocean acidication.

For comparison, in the Red Sea, the surface average pH was 8.10.02 during winter with higher values in the north due to lower temperatures and high A(T) and C(T). The Ar and Ca were around 4.120.02 and 6.20.15, respectively, with highest values in the central part of the basin caused by higher temperatures. Summer surface pH was 8.070.03, with higher values in the north and the south due to relatively low temperature. In the central of the Red Sea, pH was low due to the convergence (high temperature). The  Ar and Ca were averaged to 4.60.3 and 6.950.35, respectively, with higher values in the south and north. This is attributed to the high biological productivity in the south and the high temperature in the center of the Red Sea.

The vertical distributions of Ar, and Ca showed that the Arabian Sea is undersaturated with respect to aragonite below 600 m and calcite below 3500 m, whereas the Red Sea is supersaturated throughout the water column. In both seas pH was higher in the surface layers due to the consumption of CO2 by photosynthesis, but decreased rapidly in subsurface waters due to the release of CO2 by respiration processes. Between about 100 and 1500 m in the Arabian Sea pH is nearly constant due to the counteracting eects of decreasing temperatures and oxidation of the organic matter. The temperature effect on pH is about 0.015 units per 1C both in the Arabian Sea and Red Sea. Thus, the 0.5C warming reported for the Arabian Sea between 1904 and 1994, theoretically would result in a pH reduction of about 0.007, but the temporal coverage of the available data is unfortunately too short to verify this.

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Calcite and aragonite saturation states of the Red Sea and biogeochemical impacts of excess carbon dioxide

This chapter discusses the saturation states of the Red Sea with respect to both calcite and aragonite and their possible biogeochemical impacts as a result of ocean carbonate chemistry changes. The saturation levels of the Red Sea surface waters are several-fold supersaturated with respect to calcite and aragonite; they range from 634 to 721 % and from 446 to 488 %, respectively. The saturation levels of the deep waters range from 256 to 341 % with respect to calcite and from 177 to 230 % with respect to aragonite. They generally increase from south to the north. The lowest values of seawater supersaturation with respect to both calcite and aragonite were found at water depths >1,400 m. Changes in the seawater acid–base chemistry due to excess CO2 emission and oceanic acidification affect the saturation states of calcium carbonate. Based on reported results of the excess CO2 sink in the northern part of the Red Sea (Krumgalz et al. 1990), the estimated degree of saturation with respect to calcite and aragonite was higher by 1.9 ± 0.4 % at >200 m, 4.9 ± 0.7 % at 200–600 m, and 2.5 ± 0.1 % at >600 m in preindustrial times than in 1982. A projected drop in pH by a 0.1 unit decreases the saturation level by a factor of 1.2, whereas a drop by 0.4 pH unit decreases the saturation level by a factor of 2.1. These changes in saturation levels will have major impacts on the calcifying pelagic and benthic organisms as well as the distribution and depth of coral reefs. Low magnesian calcite and pure calcite are expected to be the dominant carbonate minerals at these low supersaturation levels.

Continue reading ‘Calcite and aragonite saturation states of the Red Sea and biogeochemical impacts of excess carbon dioxide’


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