High rates of carbon and dinitrogen fixation suggest a critical role of benthic pioneer communities in the energy and nutrient dynamics of coral reefs
Karcher, Denis B.
Voolstra, Christian R.
KAUST DepartmentMarine Science Program
Red Sea Research Center (RSRC)
Biological and Environmental Sciences and Engineering (BESE) Division
Embargo End Date2021-07-02
Permanent link to this recordhttp://hdl.handle.net/10754/663984
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Abstract1. Following coral mortality in tropical reefs, pioneer communities dominated by filamentous and crustose algae efficiently colonize substrates previously occupied by coral tissue. This phenomenon is particularly common after mass coral mortality following prolonged bleaching events associated with marine heatwaves. 2. Pioneer communities play an important role for the biological succession and reorganization of reefs after disturbance. However, their significance for critical ecosystem functions previously mediated by corals, such as the efficient cycling of carbon (C) and nitrogen (N) within the reef, remains uncertain. 3. We used 96 carbonate tiles to simulate the occurrence of bare substrates after disturbance in a coral reef of the central Red Sea. We measured rates of C and dinitrogen (N2) fixation of pioneer communities on these tiles monthly over an entire year. Coupled with elemental and stable isotope analyses, these measurements provide insights into macronutrient acquisition, export, and the influence of seasonality. 4. Pioneer communities exhibited high rates of C and N2 fixation within 4 – 8 weeks after the introduction of experimental bare substrates. Ranging from 13 to 25 μmol C cm−2 d−1 and 8 to 54 nmol N cm−2 d−1, respectively, C and N2 fixation rates were comparable to reported values for established Red Sea coral reefs. This similarity indicates that pioneer communities may quickly compensate for the loss of benthic productivity by corals. Notably, between 40 and 85% of fixed organic C was exported into the environment, constituting a vital source of energy for the coral reef food web. 5. Our findings suggest that benthic pioneer communities may play a crucial, yet overlooked role in the C and N dynamics of oligotrophic coral reefs by contributing to the input of new C and N after coral mortality. While not substituting other critical ecosystem functions provided by corals (e.g. structural habitat complexity and coastal protection), pioneer communities likely contribute to maintaining coral reef nutrient cycling through the accumulation of biomass and import of macronutrients following coral loss.
CitationRoth, F., Karcher, D. B., Rädecker, N., Hohn, S., Carvalho, S., Thomson, T., … Wild, C. (2020). High rates of carbon and dinitrogen fixation suggest a critical role of benthic pioneer communities in the energy and nutrient dynamics of coral reefs. Functional Ecology. doi:10.1111/1365-2435.13625
SponsorsWe are grateful to the personnel from the King Abdullah University of Science and Technology (KAUST) Coastal and Marine Resources Core (CMOR) Lab for logistical support. The authors would also like to acknowledge Luis Ribeiro da Silva, Rodrigo Villalobos, and João Cúrdia who helped during fieldwork. We thank Marianne Falk from the Museum für Naturkunde, Berlin, for her help in preparing and measuring elemental and isotope samples. We would like to thank the three anonymous reviewers for their helpful suggestions and comments. The research was supported by KAUST baseline funding to BHJ, and by grant Wi 2677/9-1 from the German Research Foundation (DFG) to CW.