Primary productivity of reef‐building crustose coralline algae

Abstract

The primary productivity of four species of crustose coralline algae was measured as a function of depth (0–18m) and irradiance on samples collected from and growing upon the windward coral reef at Lizard Island, northern Great Barrier Reef, Australia. Significantly higher productivities were measured in the field than in the laboratory. Maximum gross oxygen production in situ varied from 12.8 to 22.8 mmol m−2 h−1; dark respiration consumed between 2.7 and 4.5 mmol O2 m−2 h−1. Integration of photosynthesis‐irradiance models with half sine curve approximations of whole‐day irradiance yielded estimated in situ net productivities of 15–132 mmol O2 m−2 d−1. When multiplied by previously determined photosynthetic quotients, in situ net carbon fixation was estimated to vary from 0.2 to 1.3 g m−2 d−1. Multiplying these rates by measured surface relief factors of 3.1 for the reef crest and 5.0 for the windward slope yielded estimated contributions to reef organic production of ~0.9–5 g C (net) planar m−2 d−1 over the depth interval 0–18 m, given 100% cover. These data suggest that crustose coralline algae make a larger contribution to organic production on coral reefs than has been thought to this time. A curvilinear model is presented that enables their primary productivity to be estimated from measurements of in situ irradiance at the solar zenith.