Effects of nitrate and phosphate availability on the tissues and carbonate skeleton of scleractinian corals

• Published in: Marine ecology. Progress series (Halstenbek) 2017-04, Vol.570, p.101-112
• Main Authors: Tanaka, Yasuaki, Grottoli, Andréa G., Matsui, Yohei, Suzuki, Atsushi, Sakai, Kazuhiko
• Format: Article
• Language: English
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps12079

To study the effects of nutrient availability on scleractinian corals, fragments of Montipora digitata and Porites cylindrica were cultured in nutrient-enriched seawater (nitrate: 1.4 to 1.9 μmol l−1 and phosphate: 0.1 μmol l−1) for 2 mo under laboratory conditions. For both coral species, the chlorophyll a concentration of the endosymbiotic algae increased significantly in both nitrogen only (+N) and nitrogen plus phosphorus (+NP) treatments compared to the control. Endosymbiont carbon (C) content of M. digitata increased only under +NP conditions, indicating that phosphorus (P) was limiting the production of endosymbiont cells. Host C and nitrogen (N) contents were not affected by nutrient enrichment for both coral species, suggesting that the moderate nutrient enrichment did not contribute considerably to the production of host tissue. C stable isotope ratios (δ13C) of the endosymbionts and host gradually decreased during the experiment, and even more so in the +N treatment. This suggests that the coral host preferentially catabolized δ13C-enriched organic matter, such as storage lipids, and that this catabolism was enhanced when the N:P ratio of available nutrients was not balanced. Finally, the skeletal δ13C was also positively correlated with the host and endosymbiont δ13C values, which implies that the δ13C of host tissue was at least partially affecting the skeletal δ13C. Overall, moderate nutrient enrichment should not have a negative effect on coral metabolism provided that the N:P ratio of available nutrients is balanced.