The influence of seasonality on benthic primary production in a Red Sea coral reef

Northern Red Sea coral reefs experience pronounced seasonal variations in environmental factors such as water temperature, light intensity, and nutrient availability. This allows studying related effects on primary production by different functional groups. The present study therefore quantified primary production of all dominant benthic primary producers from a Jordanian fringing reef (29 degrees 27' 31 '' N, 34 degrees 58' 26 '' E) by measuring net photosynthesis (P-n) and dark respiration (R) using stirred respirometry chamber incubations during all four seasons of 2013. Annual mean P-n was highest for the macroalga Caulerpa (901 nmol O-2 cm(-2) h(-1)) and lowest for both the soft coral Sarcophyton and sedimentary microphytobenthos (212 and 223 nmol O-2 cm(-2) h(-1), respectively). Sedimentary microphytobenthos exhibited the strongest response to seasonality with 5.7 times higher P-n in spring than in winter. R was highest in hard corals among all groups in every season, likely due to nighttime calcification and heterotrophic activity. Gross photosynthesis-to-respiration ratios (P-g:R) were highest for turf algae and macroalgae as well as cyanobacterial mats. While R was primarily positively related to PAR and temperature and P-g:R to inorganic nutrients, few groups revealed significant relations between P-n and environmental parameters. Seasonal budgets found daily gross primary production and respiration to be dominated by hard and soft corals. Total reef gross primary production was comparable between less oligotrophic spring and more oligotrophic summer. This indicates that processes such as heterotrophic feeding and microbial dinitrogen fixation may help the functional groups overcome potential nutrient limitation of primary production in summer.