Imbalanced coral growth between organic tissue and carbonate skeleton caused by nutrient enrichment

Abstract

Effects of moderate nutrient enrichment (NO { 3 : ,5 mmol L 21 , PO 3{ 4 : ,0.3 mmol L 21 ) on two carbon (C) fixation rates (photosynthesis and calcification) of the zooxanthellate coral Acropora pulchra were investigated under laboratory conditions. The coral branches were incubated in the nutrient condition for three different periods (0, 5, 10 d) to observe changes in tissue biomass and zooxanthellate chlorophyll a (Chl a) concentration. Next, the incubated corals were simultaneously transferred to nutrient-depleted seawater containing 13 C-labeled dissolved inorganic carbon to assay net photosynthesis and calcification rates. Chl a concentration per unit surface area increased 2.6-fold for the 10-d enrichment, and net photosynthetic rates were also stimulated up to a similar level (2.8-fold). Tissue biomass of the host coral and zooxanthellae was approximately doubled during the period. On the other hand, calcification rates only increased 1.3-fold, suggesting that even moderate nutrient loading resulted in one-sided enhancement of the algal photosynthetic activity. The measured C fixation ratios of organic C : skeletal C were higher than the structural ratios, and the inconsistency became greater as Chl a concentration increased. The increased photosynthetic products could be excessively stored in the organic tissue and/or released into the ambient seawater.

The response of the scleractinian coralTurbinaria reniformisto thermal stress depends on the nitrogen status of the coral holobiont

“…In a few experiments involving a moderate increase in nitrogen and/or phosphorus levels, an enhancement of coral metabolism was instead observed (Meyer and Schultz, 1985;Tanaka et al, 2007;Godinot et al, 2011). Our results with non-stressed nubbins of T. reniformis (C-26 and N-26 samples) add to the growing body of evidence that a slight increase in nutrient concentration in seawater does not necessarily impact coral health.…”

“…Nitrogen-enriched corals, however, presented a decrease in organic carbon release, likely due, in the present experiment, to a higher utilization of photosynthetically acquired carbon, in combination with nitrogen, to form molecules of interest such as proteins. Three other studies have investigated the release of organic carbon by scleractinian corals in the presence of elevated nutrient concentrations (Tanaka et al, 2007;Naumann et al, 2010;Bednarz et al, 2012), and have also observed a reduced release or an increased uptake of organic carbon. In Bednarz et al (Bednarz et al, 2012), it was hypothesized that the enhanced uptake of dissolved organic carbon by the soft coral Xenia under nitrogen enrichment was due to a need for additional carbon compounds following the decrease in photosynthetic rates and carbon translocation of the symbionts.…”

“…In this last study, a lack of phosphate in nitrogen-rich seawater induced bleaching. Therefore, it was shown that moderate seawater enrichment in nitrogen (or phosphorus) can enhance coral photosynthesis and calcification (Tanaka et al, 2007;Godinot et al, 2009). Corals also have thicker tissue in nutrient-rich waters (Sawall et al, 2011).…”

Long-term effects of nutrient and CO2 enrichment on the temperate coral Astrangia poculata (Ellis and Solander, 1786)

“…Marubini and Davies, 1996;Reynaud et al, 2003;Houlbreque et al, 2004;Tanaka et al, 2007). Such results point to the importance of multiple factors in determining rates of coral calcification.…”

Inorganic nutrient availability affects organic matter fluxes and metabolic activity in the soft coral genus Xenia

“…Under low ambient inorganic nutrient concentrations, zooxanthellae metabolism and growth are limited with respect to nitrogen, and carbon is photosynthetically fixed in excess. This surplus in carbon is translocated to the host together with small amounts of nitrogen Stimson and Kinzie, 1991;Tanaka et al, 2006). At elevated inorganic nitrogen levels in ambient seawater, zooxanthellae are enabled to retain more carbon for their own metabolism and growth, and consequently less of it is being translocated to their host (Dubinsky and Jokiel, 1994).…”