Inorganic nutrient availability affects organic matter fluxes and metabolic activity in the soft coral genus Xenia.
The release of organic matter (OM) by scleractinian corals represents a key physiological process that importantly contributes to coral reef ecosystem functioning, and is affected by inorganic nutrient availability. Although OM fluxes have been studied for several dominant reef taxa, no information is available for soft corals, one of the major benthic groups in tropical reef environments. Thus, this study investigates OM fluxes along with other key physiological parameters (i.e. photosynthesis, respiration and chlorophyll a tissue content) in the common soft coral genus Xenia after a 4-week exposure period to elevated ammonium (N; 20.0 μmol l(-1)), phosphate (P; 2.0 μmol l(-1)) and combined inorganic nutrient enrichment treatment (N+P). Corals maintained without nutrient enrichment served as non-treated controls and revealed constant uptake rates for particulate organic carbon (POC) (-0.315±0.161 mg POC m(-2) coral surface area h(-1)), particulate nitrogen (PN) (-0.053±0.018 mg PN m(-2) h(-1)) and dissolved organic carbon (DOC) (-4.8±2.1 mg DOC m(-2) h(-1)). Although DOC uptake significantly increased in the N treatment, POC flux was not affected. The P treatment significantly enhanced PN release as well as photosynthesis and respiration rates, suggesting that autotrophic carbon acquisition of zooxanthellae endosymbionts influences OM fluxes by the coral host. Our physiological findings confirm the significant effect of inorganic nutrient availability on OM fluxes and key metabolic processes for the soft coral Xenia, and provide the first clues on OM cycles initiated by soft corals in reef environments exposed to ambient and elevated inorganic nutrient concentrations.
Coral Reef Ecology Group, University of Bremen and Leibniz Center for Tropical Marine Ecology, Fahrenheitstrasse 6, 28359 Bremen, Germany. vanessa.bednarz@zmt-bremen.de
Vanessa N
VN
Bednarz
Malik S
MS
Naumann
Wolfgang
W
Niggl
Christian
C
Wild
D000818:Animals; D037421:Anthozoa / Q000378:metabolism*; D002244:Carbon / Q000378:metabolism*; D057894:Coral Reefs; D017753:Ecosystem; D058086:Microalgae / Q000502:physiology; D009930:Organic Chemicals; D052638:Particulate Matter; D010710:Phosphates; D000644:Quaternary Ammonium Compounds; D012623:Seawater; D013559:Symbiosis
D009930:Organic Chemicals; D052638:Particulate Matter; D010710:Phosphates; D000644:Quaternary Ammonium Compounds; D002244:Carbon