NITROGEN ACQUISITION AND TRANSLOCATION WITHIN THE SCLERACTINIAN CORAL DIPLORIA LABYRINTHIFORMIS

Corals are able to thrive in oligotrophic waters due to their relationship with endosymbiotic dinoflagellates (Symbiodiniaceae). The coral-algal partnership depends on a delicate nutrient balance between internal nitrogen (N) recycling and N availability. Previous studies suggest that the host is the main N source for the algae; keeping symbionts N limited controls symbiont density, ensuring their excess photosynthate is translocated to the host. With reefs experiencing increasing nutrient pollution, it is essential to understand how the coral holobiont maintains a nutrient balance. Here under both in situ and nitrate (NO₃^-) enriched reef conditions, we explored the role of nutritional mode (autotrophy vs. heterotrophy) in acquiring N and the fate of N in the holobiont. Using outdoor incubations, Diploria labyrinthiformis was exposed for 24 h to four experimental treatments using ¹⁵N tracer to label either zooplankton or NO₃^- (the form of inorganic N available to symbiont but not host). NO₃^- was taken up by the symbionts but was not translocated to the host. The coral fed on zooplankton and some zooplankton-N was quickly (< 3 h) transferred to the symbionts (likely as ammonium, NH₄⁺) in both low and high NO₃^- conditions. Thus, ambient NO₃^- did not affect the symbionts’ preference for recycled nitrogen waste (NH₄⁺) from the host. By tracing the fate of N when both nutritional modes were available, we found that N can be taken up both ways but is conserved within the symbionts if acquired through autotrophy and translocated from host to symbionts if acquired through feeding.

Presentation Preference: Oral

Primary Presenter: Moriah Kunes, Princeton University (mkunes@princeton.edu)

Authors:

Moriah Kunes, Princeton University  (mkunes@princeton.edu)

Hua-Xia Sheng, Xiamen University  (hxsheng@xmu.edu.cn)

Tacy Guest, Princeton University  (tg4777@princeton.edu)

Yvonne Sawall, Arizona State University Bermuda Institute of Ocean Sciences  (yvonne.sawall@bios.asu.edu)

Bess Ward, Princeton University  (bbw@princeton.edu)