Nitrogen and phosphorus ecophysiology of coralline algae

The characteristics of nutrient uptake in macroalgae are generally well known but surprisingly little is known about nutrient uptake in coralline algae despite their ecological importance and extensive depth distribution. This study provides the first information on nitrate, ammonium and phosphate storage and uptake by articulated and crustose coralline algae that are dominant features of temperate subtidal rocky reefs. A comparison was made between an articulated coralline alga, Arthrocardia sp. in the Corallinales and crustose coralline spp. within the Hapalidiales. Seawater nutrient concentration and nutrient storage by coralline algae were monitored between June 2016 and November 2017 in a kelp forest in southern New Zealand. Time-course nutrient depletion experiments were conducted to determine appropriate incubation times for multiple-flask experiments and evaluate maximal uptake of nitrate, ammonium, and phosphate over time in winter and summer. The uptake of ammonium exhibited a saturable kinetics with Vmax of Arthrocardia sp. (2.07 ± 0.32 μmol gDW−1 h−1) significantly higher than that of crustose coralline spp. (0.58 ± 0.17 μmol gDW−1 h−1). A linear relationship with concentration was observed in nitrate and phosphate uptake by both coralline algae. Ammonium was considered a preferred nitrogen source for these corallines compared with nitrate in both summer and winter. Morphological difference is suggested to be an important factor resulting in the difference in nitrogen and phosphorus uptake rates and kinetic parameters of these corallines. Further research is required to understand if these differences are general attributes of the functional ecology of crustose and articulated corallines.