In situ eutrophication stimulates dinitrogen fixation, denitrification, and productivity in Red Sea coral reefs
Type
ArticleAuthors
El-Khaled, Yusuf C.Roth, Florian

Tilstra, Arjen
Radecker, Nils
Karcher, Denis B.
Kürten, Benjamin

Jones, Burton

Voolstra, Christian R.

Wild, Christian
KAUST Department
Biological and Environmental Sciences and Engineering (BESE) DivisionMarine Science Program
Red Sea Research Center (RSRC)
Reef Genomics Lab
Date
2020-04-30Online Publication Date
2020-04-30Print Publication Date
2020-07-09Embargo End Date
2025-04-30Submitted Date
2020-01-24Permanent link to this record
http://hdl.handle.net/10754/664520
Metadata
Show full item recordAbstract
Eutrophication (i.e. the increase of [in-]organic nutrients) may affect the functioning of coral reefs, but knowledge about the effects on nitrogen (N) cycling and its relationship to productivity within benthic reef communities is scarce. Thus, we investigated how in situ manipulated eutrophication impacted productivity along with 2 counteracting N-cycling pathways (dinitrogen [N2]-fixation, denitrification), using a combined acetylene assay. We hypothesised that N2-fixation would decrease and denitrification increase in response to eutrophication. N fluxes and productivity (measured as dark and light oxygen fluxes assessed in incubation experiments) were determined for 3 dominant coral reef functional groups (reef sediments, turf algae, and the scleractinian coral Pocillopora verrucosa) after 8 wk of in situ nutrient enrichment in the central Red Sea. Using slow-release fertiliser, we increased the dissolved inorganic N concentration by up to 7-fold compared to am bient concentrations. Experimental nutrient enrichment stimulated both N2-fixation and denitrification across all functional groups 2-to 7-fold and 2-to 4-fold, respectively. Productivity doubled in reef sediments and remained stable for turf algae and P. verrucosa. Our data therefore suggest that (1) turf algae are major N2-fixers in coral reefs, while denitrification is widespread among all investigated groups; (2) surprisingly, and contrary to our hypothesis, both N2-fixation and denitrification are involved in the response to moderate N eutrophication, and (3) stimulated N2-fixation and denitrification are not directly influenced by productivity. Our findings underline the importance and ubiquity of microbial N cycling in (Red Sea) coral reefs along with its sensitivity to eutrophication.Citation
El-Khaled, Y., Roth, F., Tilstra, A., Rädecker, N., Karcher, D., Kürten, B., … Wild, C. (2020). In situ eutrophication stimulates dinitrogen fixation, denitrification, and productivity in Red Sea coral reefs. Marine Ecology Progress Series, 645, 55–66. doi:10.3354/meps13352Sponsors
This work was funded by the German Research Association (DFG Project: Wi 2677/9-1) to C.W. and KAUST baseline funding to B.H.J. and C.R.V. We are thankful to Rüdiger Willhaus for his expertise in graph visualisation, and to Najeh Kharbatia for technical support.Publisher
Inter-Research Science CenterJournal
Marine Ecology Progress SeriesAdditional Links
https://www.int-res.com/abstracts/meps/v645/p55-66/ae974a485f413a2113503eed53cd6c53
10.3354/meps13352