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Ocean Sampling Day was initiated by the EU-funded Micro B3 (Marine Microbial Biodiversity, Bioinformatics, Biotechnology) project to obtain a snapshot of the marine microbial biodiversity and function of the world’s oceans. It is a simultaneous global mega-sequencing campaign aiming to generate the largest standardized microbial data set in a single day. This will be achievable only through the coordinated efforts of an Ocean Sampling Day Consortium, supportive partnerships and networks between sites. This commentary outlines the establishment, function and aims of the Consortium and describes our vision for a sustainable study of marine microbial communities and their embedded functional traits.

We report N(2) fixation rates measured from two stations monitored monthly off the Mediterranean coast of Israel during 2006 and 2007, and along a transect from Israel to Crete in September 2008. Analyses of time-series data revealed expression of nifH genes from diazotrophs in nifH clusters I and II, including cyanobacterial bloom-formers Trichodesmium and diatom-Richelia intracellularis associations. However, nifH gene abundance and rates of N(2) fixation were very low in all size fractions measured (> 0.7 µm). Volumetric (15) N uptake ranged from below detection (∼ 36% of > 300 samples) to a high of 0.3 nmol N l(-1) d(-1) and did not vary distinctly with depth or season. Areal N(2) fixation averaged ∼ 1 to 4 µmol N m(-2) d(-1) and contributed only ∼ 1% and 2% of new production and ∼ 0.25% and 0.5% of primary production for the mixed (winter) and stratified (spring-fall) periods respectively. N(2) fixation rates along the 2008 east-west transect were also extremely low (0-0.04 nmol N l(-1) d(-1), integrated average 2.6 µmol N m(-2) d(-1) ) with 37% of samples below detection and no discernable difference between stations. We demonstrate that diazotrophy and N(2) fixation contribute only a minor amount of new N to the P impoverished eastern Mediterranean Sea.

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Coral reefs are exposed to many anthropogenic stresses increasing in impact and range, both on local and regional scales. The main ones discussed here are nutrient enrichment, sewage disposal, sedimentation, oil-related pollution, metals and thermal pollution. The stress comprising the main topic of this article, eutrophication, is examined from the point of view of its physiological and ecological mechanisms of action, on a number of levels. Nutrient enrichment can introduce an imbalance in the exchange of nutrients between the zooxanthellae and the host coral, it reduces light penetration to the reef due to nutrient-stimulated phytoplankton growth, and, most harmful of all, may bring about proliferation of seaweeds. The latter rapidly outgrow, smother and eventually replace, the slow-growing coral reef, adapted to cope with the low nutrient concentrations typical in tropical seas.Eutrophication seldom takes place by itself. Sewage disposal invariably results in nutrient enrichment, but it also enriches the water with organic matter which stimulates proliferation of oxygen-consuming microbes. These may kill corals and other reef organisms, either directly by anoxia, or by related hydrogen sulfide production. Increased sediment deposition is in many cases associated with other human activities leading to eutrophication, such as deforestation and topsoil erosion.Realistically achievable goals to ensure conservation, and in some instances, rehabilitation of coral reefs are listed.

The coupling between CO2 and Ca2+ exchange and photosynthesis by corals (Favia sp.) was studied with microsensors for Ca2+, 02, pH and COz. The profiles of these compounds, measured perpendicular on the coral surface, were strongly influenced by light. During illumination, the concentration of O2 and the pH at the polyp surface was higher than in the surrounding seawater, while the concentrations of Ca2+ and CO2 were lower. In the dark the inverse was observed. Furthermore, simultaneous recordmg of concentration changes at the coral surface, in response to light and inhibitors, were performed with pairs of the sensors. The concentration changes of CO2 and pH were slow, while those of Ca2+ and O2 were immediate and fast. The concentration changes of the O2 and Ca2+ concentrations at the coral surface were synchronous in response to changes in light condtions and to inhibition of the photosynthesis. Also, the spatial distribution of photosynthetic activity over a single polyp coincided with the distribution of CaZ' concentration changes. These results show that Ca2+ dynamlcs at the polyp surface is not an indirect effect of increased CaC03 precipitation at the skeleton, but ~n d icates the presence of a Ca2+ uptake mechanism that is directly correlated to photosynthesis. Inhibition of carbonic anhydrase strongly decreased photosynthesis, especially at higher light intensihes. This, comb~ned with the observed increase in CO2 concentration changes and absolute increase in CO2 concentration at the tissue surface, demonstrated the importance of carbonic anhydrase for C02/D1C uptake and transport to the site of photosynthesis.