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N 2 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 N 2 fixation. This study quantified N 2 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. N 2 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 C 2 H 4 cm-2 h-1) and coral rock (3.5±2.8 nmol C 2 H 4 cm-2 h-1) compared to M. fistulifera (0.2±0.2 nmol C 2 H 4 cm-2 h-1). There was strong seasonality in N 2 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 …