River systems connect the terrestrial biosphere, the atmosphere and the ocean in the global carbon cycle. A recent estimate suggests that up to 3 petagrams of carbon per year could be emitted as carbon dioxide (CO2) from global inland waters, offsetting the carbon uptake by terrestrial ecosystems. It is generally assumed that inland waters emit carbon that has been previously fixed upstream by land plant photosynthesis, then transferred to soils, and subsequently transported downstream in run-off. But at the scale of entire drainage basins, the lateral carbon fluxes carried by small rivers upstream do not account for all of the CO2 emitted from inundated areas downstream. Three-quarters of the world's flooded land consists of temporary wetlands, but the contribution of these productive ecosystems to the inland water carbon budget has been largely overlooked. Here we show that wetlands pump large amounts of atmospheric CO2 into river waters in the floodplains of the central Amazon. Flooded forests and floating vegetation export large amounts of carbon to river waters and the dissolved CO2 can be transported dozens to hundreds of kilometres downstream before being emitted. We estimate that Amazonian wetlands export half of their gross primary production to river waters as dissolved CO2 and organic carbon, compared with only a few per cent of gross primary production exported in upland (not flooded) ecosystems. Moreover, we suggest that wetland carbon export is potentially large enough to account for at least the 0.21 petagrams of carbon emitted per year as CO2 from the central Amazon River and its floodplains. Global carbon budgets should explicitly address temporary or vegetated flooded areas, because these ecosystems combine high aerial primary production with large, fast carbon export, potentially supporting a substantial fraction of CO2 evasion from inland waters.

Metabolic interactions with endosymbiotic photosynthetic dinoflagellate Symbiodinium spp. are fundamental to reef-building corals (Scleractinia) thriving in nutrient-poor tropical seas. Yet, detailed understanding at the single-cell level of nutrient assimilation, translocation, and utilization within this fundamental symbiosis is lacking. Using pulse-chase 15N labeling and quantitative ion microprobe isotopic imaging (NanoSIMS; nanoscale secondary-ion mass spectrometry), we visualized these dynamic processes in tissues of the symbiotic coral Pocillopora damicornis at the subcellular level. Assimilation of ammonium, nitrate, and aspartic acid resulted in rapid incorporation of nitrogen into uric acid crystals (after ~45 min), forming temporary N storage sites within the dinoflagellate endosymbionts. Subsequent intracellular remobilization of this metabolite was accompanied by translocation of nitrogenous compounds to the coral host, starting at ~6 h. Within the coral tissue, nitrogen is utilized in specific cellular compartments in all four epithelia, including mucus chambers, Golgi bodies, and vesicles in calicoblastic cells. Our study shows how nitrogen-limited symbiotic corals take advantage of sudden changes in nitrogen availability; this opens new perspectives for functional studies of nutrient storage and remobilization in microbial symbioses in changing reef environments.

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Surface sediments and marine invertebrates, collected from 2 intertidal flats on Okinawa Island, 1 adjacent to a mangrove system, were analysed for fatty acid composition. The detection of fatty acid markers found in mangrove leaves in the organic matter of the surface sediments, coupled with measurements of C:N ratios, showed that organic matter from the mangrove forest (in Oura Bay) is exported to the intertidal flat in both the rainy season and the dry season. This export seems to be higher in the rainy season. However, bacteria, diatoms and macroalgae were the main food source in the surface sediments, as shown by the contribution of their respective fatty acid markers. These markers were also detected in the tissues of the dominant macrozoobenthic species, fiddler crabs and gastropods. Bacteria and green macroalgae were the primary food sources ingested at both sites, irrespective of season. The organic matter derived from mangroves was also ingested by the macrozoobenthos of Oura Bay, while markers of higher plants were not found in the tissues of invertebrate species at Itoman intertidal flat, the site that was not adjacent to a mangrove system.

) and highest condition indices (mean K = 1.19; TAG:ST = 2.18) at the Authie, Canche and Somme estuaries. The indices measured in this study correlated well with anthropogenic disturbance and may provide a useful tool to assess habitat quality. Sites with highest sediment chemical contaminants had the lowest habitat quality and, through growth and lipid-storage limitation, could dramatically lower over-winter survival of the juveniles living in these nursery grounds.

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