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Marine Ecology Progress Series

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MEPS 527:47-57 (2015)  -  DOI:

Dinitrogen fixation and primary productivity by carbonate and silicate reef sand communities of the Northern Red Sea

Vanessa N. Bednarz1,*, Nanne van Hoytema1, Ulisse Cardini1, Malik S. Naumann1, Mamoon M. D. Al-Rshaidat2,3, Christian Wild1,4

1Coral Reef Ecology Group (CORE), Leibniz Center for Tropical Marine Ecology (ZMT), Fahrenheitstr. 6, 28359 Bremen, Germany
2Laboratory for Molecular Microbial Ecology (LaMME), Marine Science Station, Aqaba 77110, Jordan
3Department of Marine Biology, The University of Jordan - Aqaba Branch, Aqaba 77110, Jordan
4Faculty of Biology and Chemistry (FB 2), University of Bremen, NW 2 / Leobener Str., 28359 Bremen, Germany
*Corresponding author:

ABSTRACT: Permeable sediments are highly bioactive compartments in coral reefs. The associated dense microbial communities sustain fast degradation of organic matter, thereby playing a key role in nutrient recycling within the reef. Besides nutrient recycling, new nutrients (i.e. nitrogen) are acquired by dinitrogen (N2) fixing microbial communities, but knowledge about the influence of sand mineralogy and key environmental factors on this process is scarce. Therefore, this study quantified seasonal N2 fixation (via acetylene reduction) along with gross photosynthesis (via O2 fluxes) by adjacent carbonate and silicate sands in a Northern Red Sea coral reef. Findings revealed significantly higher N2 fixation in carbonate than in silicate sands (2.88 and 1.52 nmol C2H4 cm-2 h-1, respectively) and a more pronounced seasonal response in the former, likely caused by its higher permeability, grain size and microbial abundance. Ambient light and organic matter availability were the main controlling environmental factors for sand-associated N2 fixation. Carbonate and silicate sands showed similar gross photosynthesis rates (270 and 233 nmol O2 cm-2 h-1) that positively (carbonate sands) or negatively (silicate sands) correlated with N2 fixation, likely due to different diazotrophic communities. Seasonal appearance of microbial mats on carbonate sands increased N2 fixation and gross photosynthesis by up to one order of magnitude. On an annual average, carbonate and silicate sands obtain ~8% and microbial mat communities obtain ~13% of their photo-metabolic N demand via N2 fixation. 

KEY WORDS: Carbonate sand · Silicate sand · Gulf of Aqaba · Microphytobenthos · Photosynthesis · Seasonality · Oxygen fluxes · Acetylene reduction

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Cite this article as: Bednarz VN, van Hoytema N, Cardini U, Naumann MS, Al-Rshaidat MMD, Wild C (2015) Dinitrogen fixation and primary productivity by carbonate and silicate reef sand communities of the Northern Red Sea. Mar Ecol Prog Ser 527:47-57.

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