Hot off the presses: Amino Acid Compound Specific #Isotope Analysis (#AACSIA) to understand #coral nutrition. We show corals are reliant on symbiont-derived carbon and nitrogen for AA. Flexible nutrition? Not so much. @GatesCoralLab @himb_soest bit.ly/3uxZOe2
Amino acids in the AACSIA terminology are essential (from diets) or non-essential (synthesized) for carbon, and either trophic (change with feeding) or source (reflect origins) for nitrogen. At the time of our experiment no one had tested C and N AACSIA in corals.
Corals are weird. They can produce a lot of AA, most animals can't. Their symbionts also produce nearly all AA, as they are plants. So together the holobiont may produce everything "in house" or source building blocks from feeding on plankton.
AACSIA offer a tool to test (1) the sources of nutrition, (2) changes in diet, (3) and avoid the mixed up and muddy effects that plague bulk isotope data (fractionation, sources, space and time...). For corals AACSIA could be a game changer. It has done as much for other fields!
We modified nutrition of corals to produce autotrophic, mixotrophic, heterotrophic treatments and found that the rice coral (Montipora capitata) is heavily reliant on symbiont-nutrition for nearly ALL amino acids, including C and N sources. WHOA.
How similar are the host and symbiont AACSIA isotope values relative to the plankton food source? Almost identical. This suggests this coral is relying on symbionts for the essential (carbon) and trophic (nitrogen) AA and other AA are produced by holobiont (who? hard to say...) 
This was surprising as another excellent study showed trophic plasticity and heterotrophy in general could be determined using these essential amino acids. Why were our results so different? Turns out our corals are simply molecularly quite distinct-- autotrophic fidelity!
We pulled data from Palmyra, the Red Sea, corals, symbionts, holobionts, plankton and particulates... We found that AACSIA were all showing contrasting patterns of nutrition based on coral species but the signatures of heterotrophic food was very consistent. CORALS are wild.
This led to new questions. If the corals are so different, what about their symbionts? How do they relate to other autotrophic plankton? Pulling data from every study we could find, we show that #Symbiodiniaceae are also distinct relative to plankton and a unique food "source".
Overall this study (while originally limited in experimental scope) showed some very real and big findings. (1) AACSIA help us quantify coral nutrition in new ways, building a future beyond bulk isotope analyses...
(2) It helped identify that the "isotope fingerprint" (to quote Thomas Larsen @natursyn) also exists for corals and their symbionts and is shows a remarkably stable signature in food sources across space/time/studies/oceans!
Finally, (3) OPEN SCIENCE is so vital, especially in growing fields. I am eternally grateful for those that share their code and data -- @MikeD_Fox @DrKeltonMcMahon to name a few. Make your data accessible, your code open!
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