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Our understanding of the global carbon cycle has been reshaped by KAUST researchers who have helped to reveal a major role for the abundance of seaweed growing around the world's coasts. Some years ago, Carlos Duarte, now director of the Red Sea Research Center at KAUST, was among the first scientists to establish that marine vegetation plays a major role in the movement of carbon through the environment and all living organisms. The dominant players in the waters of coastal zones are macroalgae - more commonly known as seaweeds, such as kelp and sargassum. Now Duarte and Dorte Krause-Jensen from Aarhus University in Denmark have reviewed and quantified the role of macroalgae in trapping carbon. Their estimate is a highly significant 173 trillion grams of carbon sequestered in coastal seaweed, globally, per year1. "Marine macroalgae have largely been excluded from discussion of marine carbon sinks," says Duarte. He explains that this is due to neglecting the accumulation of macroalgae in deep-sea sediments. His latest review suggests that around 90 percent of global sequestration of carbon by macroalgae could be due to the transport of this vegetation into the deep sea. The researchers propose two main mechanisms for this transport - seaweed drifting through under-sea canyons and deposition by sinking when the marine vegetation loses its natural buoyancy. "These processes in many vegetated coastal habitats sequester ten times more carbon dioxide per hectare than a hectare of Amazonian forest," says Duarte. This highlights the significance of seaweed when compared to a habitat often used as a carbon sink yardstick in discussions about climate change . "Understanding the major carbon sinks in the biosphere is of paramount importance to identify where there are management opportunities to mitigate climate change," says Duarte. He explains that understanding where carbon goes provides opportunities for potential interventions that absorb more of the carbon dioxide that human activity releases into the atmosphere. This latest analysis adds to other recent insights into carbon sequestration gained by Duarte and his colleagues, including new understanding of the role of marine bacteria, and of hydrocarbons deposited into the ocean from the atmosphere (see related articles). Duarte now plans to use advanced techniques to identify and quantify the significance of macroalgal carbon deposition in existing sediments. One tool will be DNA analysis, which can reveal which species contributed to the carbon in sediments. The global importance of climate change makes such work vital for planning effective management of the planet.

Papadopoulos V.P.,Hellenic Center for Marine Research | Abualnaja Y.,Red Sea Research Center | Josey S.A.,UK National Oceanography Center | Bower A.,Woods Hole Oceanographic Institution | And 3 more authors.
Journal of Climate

The influence of the atmospheric circulation on the winter air-sea heat fluxes over the northern Red Sea is investigated during the period 1985-2011. The analysis based on daily heat flux values reveals that most of the net surface heat exchange variability depends on the behavior of the turbulent components of the surface flux (the sum of the latent and sensible heat).The large-scale composite sea level pressure (SLP) maps corresponding to turbulent flux minima and maxima show distinct atmospheric circulation patterns associated with each case. In general, extreme heat loss (with turbulent flux lower than -400 W m-2) over the northern Red Sea is observed when anticyclonic conditions prevail over an area extending from the Mediterranean Sea to eastern Asia along with a recession of the equatorial African lowssystem. Subcenters of high pressure associated with this pattern generatethe required steep SLP gradient that enhances the wind magnitude and transfers cold and dry air masses from higher latitudes. Conversely, turbulent fluxmaxima (heat loss minimization with values from -100 to -50 W m-2) are associated with prevailing low pressures over the eastern Mediterranean andan extended equatorial African low that reaches the southern part of the Red Sea. In this case, a smooth SLP field over the northern Red Sea results in weak winds over the area that in turn reduce the surface heat loss. At the same time, southerlies blowing along the main axis of the Red Sea transfer warm and humid air northward, favoring heat flux maxima. © 2013 American Meteorological Society. Source

Moreno-Ostos E.,University of Malaga | Blanco J.M.,University of Malaga | Agusti S.,CSIC - Mediterranean Institute for Advanced Studies | Agusti S.,Red Sea Research Center | And 5 more authors.
Journal of Marine Systems

Modelling the size-abundance spectrum of phytoplankton has proven to be a very useful tool for the analysis of physical-biological coupling and the vertical flux of carbon in oceanic ecosystems at different scales. A frequent observation relates high phytoplankton biovolume in productive regions with flatter spectrum slope and the opposite in oligotrophic ecosystems. Rather than this, the relationship between high biovolume phytoplankton assemblages and flatter size-abundance spectra does not correspond with measurements of the phytoplankton community in the Atlantic Ocean open waters. As part of the Malaspina Circunnavegation Expedition, sixty seven sampling stations within the Atlantic Ocean covering six oceanographic provinces, at different seasons, produced a complete set of phytoplankton size-spectra whose slope and biovolume did not show any obvious interrelation. In these oligotrophic sites, small (procaryotes) and medium-size (nanoplankton) cells are responsible for the most part of biovolume, and their response to environmental conditions does not apply to changes in the size-abundance spectrum slope as expected in richer, large-cell dominated ecosystems. © 2015 Elsevier B.V. Source

Klatt J.M.,Max Planck Institute for Marine Microbiology | Al-Najjar M.A.A.,Max Planck Institute for Marine Microbiology | Al-Najjar M.A.A.,Red Sea Research Center | Yilmaz P.,Max Planck Institute for Marine Microbiology | And 4 more authors.
Applied and Environmental Microbiology

Before the Earth's complete oxygenation (0.58 to 0.55 billion years [Ga] ago), the photic zone of the Proterozoic oceans was probably redox stratified, with a slightly aerobic, nutrient-limited upper layer above a light-limited layer that tended toward euxinia. In such oceans, cyanobacteria capable of both oxygenic and sulfide-driven anoxygenic photosynthesis played a fundamental role in the global carbon, oxygen, and sulfur cycle. We have isolated a cyanobacterium, Pseudanabaena strain FS39, in which this versatility is still conserved, and we show that the transition between the two photosynthetic modes follows a surprisingly simple kinetic regulation controlled by this organism's affinity for H2S. Specifically, oxygenic photosynthesis is performed in addition to anoxygenic photosynthesis only when H2S becomes limiting and its concentration decreases below a threshold that increases predictably with the available ambient light. The carbon-based growth rates during oxygenic and anoxygenic photosynthesis were similar. However, Pseudanabaena FS39 additionally assimilated NO3 - during anoxygenic photosynthesis. Thus, the transition between anoxygenic and oxygenic photosynthesis was accompanied by a shift of the C/N ratio of the total bulk biomass. These mechanisms offer new insights into the way in which, despite nutrient limitation in the oxic photic zone in the mid-Proterozoic oceans, versatile cyanobacteria might have promoted oxygenic photosynthesis and total primary productivity, a key step that enabled the complete oxygenation of our planet and the subsequent diversification of life. © 2015, American Society for Microbiology. Source

Voolstra C.R.,Red Sea Research Center
Molecular Ecology

The existence of coral reef ecosystems relies critically on the mutualistic relationship between calcifying cnidarians and photosynthetic, dinoflagellate endosymbionts in the genus Symbiodinium. Reef-corals have declined globally due to anthropogenic stressors, for example, rising sea-surface temperatures and pollution that often disrupt these symbiotic relationships (known as coral bleaching), exacerbating mass mortality and the spread of disease. This threatens one of the most biodiverse marine ecosystems providing habitats to millions of species and supporting an estimated 500 million people globally (Hoegh-Guldberg et al. 2007). Our understanding of cnidarian-dinoflagellate symbioses has improved notably with the recent application of genomic and transcriptomic tools (e.g. Voolstra et al. 2009; Bayer et al. 2012; Davy et al. 2012), but a model system that allows for easy manipulation in a laboratory environment is needed to decipher underlying cellular mechanisms important to the functioning of these symbioses. To this end, the sea anemone Aiptasia, otherwise known as a 'pest' to aquarium hobbyists, is emerging as such a model system (Schoenberg & Trench 1980; Sunagawa et al. 2009; Lehnert et al. 2012). Aiptasia is easy to grow in culture and, in contrast to its stony relatives, can be maintained aposymbiotically (i.e. dinoflagellate free) with regular feeding. However, we lack basic information on the natural distribution and genetic diversity of these anemones and their endosymbiotic dinoflagellates. These data are essential for placing the significance of this model system into an ecological context. In this issue of Molecular Ecology, Thornhill et al. (2013) are the first to present genetic evidence on the global distribution, diversity and population structure of Aiptasia and its associated Symbiodinium spp. By integrating analyses of the host and symbiont, this research concludes that the current Aitpasia taxonomy probably needs revision and that two distinct Aiptasia lineages are prevalent that have probably been spread through human activity. One lineage engages in a specific symbiosis with Symbiodinium minutum throughout the tropics, whereas a second, local Aiptasia sp. population in Florida appears more flexible in partnering with more than one symbiont. The existence of symbiont-specific and symbiont-flexible Aiptasia lineages can greatly complement laboratory-based experiments looking into mechanisms of symbiont selectivity. In a broader context, the study by Thornhill et al. (2013) should inspire more studies to target the natural environment of model systems in a global context targeting all participating member species when establishing ecological and genetic baselines. © 2013 John Wiley & Sons Ltd. Source

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