Marine finfish effluent bioremediation: Effects of stocking density and temperature on nitrogen removal capacity of Chondrus crispus and Palmaria palmata (Rhodophyta)

Optimal stocking density of the marine red algae Chondrus crispus and Palmaria palmata was determined to maximize productivity and nitrogen removal in a land-based Atlantic halibut farm. Both species were cultured at 0.2, 2, 4, 6 and 10 kg m− 2 for four weeks at 140 ± 10 μmol photons m− 2 s− 1 of photosynthetically active radiation (PAR) and 16:8 L:D photoperiod. For each species, two rearing temperatures were compared at different times of the year: 6 (Dec.) and 13 °C (June) for C. crispus, and 6 (Mar.) and 16 °C (July) for P. palmata. Growth rates of both species were inversely dependent on stocking density at all temperatures; however, the productivity (g fresh weight d− 1) in Chondrus was significantly higher at 2 kg m− 2 than 0.2 kg m− 2 at both temperatures. By contrast, productivity of Palmaria was independent of stocking densities of 0.2 through 6.0 kg m− 2 at both temperatures. The net N removal in Chondrus was the highest at 2.0 kg m− 2 at both temperature conditions. Palmaria also showed the highest N removal at 2.0 kg m− 2 at 6 °C but at 4.0 kg m− 2 at 16 °C. Overall, C. crispus was the better performer year-round than P. palmata in terms of productivity and nutrient removal capacity.