Coral holobiont functioning under environmental change: Determining the drivers of coral-associated denitrification - DECODE

• Applicant: Professor Dr. Christian Wild
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 459845997

Nitrogen (N) is a limiting nutrient in highly productive tropical coral reefs despite its key role for coral metabolism. This on the one hand requires efficient (re)cycling of N by coral holobionts, i.e. the coral animal with its algal symbionts (zooxanthellae) and associated microbes. On the other hand, high internal N concentrations can be detrimental to the coral holobiont by shifting from N limitation towards P limitation which may lead to e.g. increased bleaching susceptibility. Thus, the coral associated microbiome plays an important role by either providing bioavailable N through fixation of atmospheric dinitrogen (N2) or potentially alleviating the coral holobiont from excess N through denitrification. N2 fixation by diazotrophs is highly susceptible to shifts in environmental parameters, while the effects on denitrification are so far unknown. Very recent research suggests that these two key N-cycling processes occur simultaneously in coral holobionts. Surprisingly, both processes are obviously correlated and likely share a common energy source within the holobiont, i.e. photosynthates released from the zooxanthellae. Based on the available evidence, I hypothesize that a stable coral holobiont is characterized by a balance between denitrifiers, diazotrophs and zooxanthellae. A deviation from this balance can lead to an interruption of N limitation for the zooxanthellae, which may ultimately lead to reduced coral holobiont health. The proposed project DECODE (Determining the drivers of coral-associated denitrification), combines field studies in seasonal resolution and manipulative laboratory experiments. It will assess the effects of the biotic and abiotic key parameters that drive denitrification in coral holobionts and their effects on the coral microbiome. Thereby, I will apply a holistic (involving studies of all holobiont members) and interdisciplinary approach at the interface between animal physiology, microbial ecology, and biogeochemistry. Thereby, DECODE will provide fundamental knowledge on coral holobiont functioning under different environmental change scenarios.

• DFG Programme: Research Grants