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Marine Ecology Progress Series

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MEPS 533:79-92 (2015)  -  DOI:

Seasonality in dinitrogen fixation and primary productivity by coral reef framework substrates from the northern Red Sea

Laura Rix1,*, Vanessa N. Bednarz1, Ulisse Cardini1, Nanne van Hoytema1, Fuad A. Al-Horani2, Christian Wild1,3, Malik S. Naumann1

1Coral Reef Ecology Group (CORE), Leibniz Center for Tropical Marine Ecology (ZMT), Fahrenheitstr. 6, 28359 Bremen, Germany
2The University of Jordan - Aqaba and Marine Science Station (MSS), PO Box 2595, Aqaba 77110, Jordan
3Faculty of Biology and Chemistry (FB 2), University of Bremen, NW 2 / Leobener Str., 28359 Bremen, Germany
*Corresponding author:

ABSTRACT: N2 fixation by coral reef benthic substrates may support primary productivity on oligotrophic coral reefs. However, little is known regarding the influence of environmental parameters on coral reef benthic N2 fixation. This study quantified N2 fixation and photosynthesis in 3 common reef framework substrates: turf algae, coral rock, and the abundant encrusting sponge Mycale fistulifera over 4 seasons in the northern Gulf of Aqaba. N2 fixation activity was detected during day and night for all substrates, but on an annual average was significantly higher for turf algae (4.4 ± 3.9 nmol C2H4 cm-2 h-1) and coral rock (3.5 ± 2.8 nmol C2H4 cm-2 h-1) compared to M. fistulifera (0.2 ± 0.2 nmol C2H4 cm-2 h-1). There was strong seasonality in N2 fixation, with rates one order of magnitude higher in summer when temperature and irradiance were highest but inorganic nutrient concentrations lowest. During summer and fall, when nutrients were low, we found a significant positive linear relationship between gross photosynthesis (Pgross) and N2 fixation in turf algae and coral rock. Further, we estimate N2 fixation can supply up to 20 and 27% of the N demand for net photosynthesis (Pnet) in coral rock and turf algae, respectively. By contrast there was no significant relationship between N2 fixation and Pgross in M. fistulifera, which displayed negative Pnet and heterotrophic metabolism (Pgross:respiration <1). These findings highlight the role of environmental parameters in regulating benthic substrate-associated N2 fixation and the potential importance of fixed N for supporting primary production, particularly during nutrient-depleted conditions.

KEY WORDS: Acetylene reduction · Photosynthesis · Turf algae · Sponges · Coral rock · Gulf of Aqaba

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Cite this article as: Rix L, Bednarz VN, Cardini U, van Hoytema N, Al-Horani FA, Wild C, Naumann MS (2015) Seasonality in dinitrogen fixation and primary productivity by coral reef framework substrates from the northern Red Sea. Mar Ecol Prog Ser 533:79-92.

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