In situ eutrophication stimulates dinitrogen fixation, denitrification, and productivity in Red Sea coral reefs
AuthorsEl-Khaled, Yusuf C.
Karcher, Denis B.
Voolstra, Christian R.
KAUST DepartmentMarine Science Program
Biological and Environmental Sciences and Engineering (BESE) Division
Red Sea Research Center (RSRC)
Permanent link to this recordhttp://hdl.handle.net/10754/664520
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AbstractEutrophication (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.
CitationEl-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/meps13352
SponsorsThis 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.
PublisherInter-Research Science Center
JournalMarine Ecology Progress Series