Coral reef algal turfs: master producers in nutrient poor seas

Coral reef algal turfs were grown on submerged plastic screens near reef communities, in the trade wind belt of the southeastern Bahamas. Using harvest production methods, in a variety of depths and locations, mean harvest production rates up to 14 g (dry) m−2 d−1 were obtained at ambient nutrient levels below 0.2 μm for nitrogen as NO2 + NO3. A wide range in production rate was found; this resulted from light rather than nutrient differences. Peak harvest production occurs at light intensities of 1400–1700 μmol m−2 s−1, far above levels previously cited for most algae, including phytoplankton.A basic premise of biological oceanography has been that primary production in the sea, even under optimal conditions of solar radiation, is nutrient-limited and develops considerably lower levels than most plant production on land–both natural and under cultivation. However, the effects of nutrient limitation can be overcome by trade wind-driven currents, which provide an infinite nutrient source and nitrogen fixation by blue-green algae within the community. Wave surge maximizing of metabolite exchange, and perhaps light-flashing effects as well, enhance production potential. Actual harvest production demonstrated that, under these conditions, net and gross primary production can be very large even in the most nutrient-poor waters.