Data from: Trophic plasticity in a common reef-building coral: Insights from δ13C analysis of essential amino acids

1. Reef-building corals are mixotrophic organisms that can obtain
nutrition from endosymbiotic microalgae (autotrophy) and particle capture
(heterotrophy). Heterotrophic nutrition is highly beneficial to many
corals, particularly in times of stress. Yet the extent to which different
coral species rely on heterotrophic nutrition remains largely unknown
because it is challenging to quantify. 2. We developed a quantitative
approach to investigate coral nutrition using carbon isotope (δ13C)
analysis of six essential amino acids (AAESS) in a common Indo-Pacific
coral (Pocillopora meandrina) from the fore reef habitat of Palmyra Atoll.
We sampled particulate organic matter (POM) and zooplankton as the
dominant heterotrophic food sources in addition to the coral host and
endosymbionts. We also measured bulk tissue carbon (δ13C) and nitrogen
(δ15N) isotope values of each sample type. 3. Patterns among δ13C values
of individual AAESS provided complete separation between the autotrophic
(endosymbionts) and heterotrophic nutritional sources. In contrast, bulk
tissue δ13C and δ15N values were highly variable across the putative food
sources and among the coral and endosymbiont fractions, preventing
accurate estimates of coral nutrition on Palmyra. 4. We used linear
discriminant analysis to quantify differences among patterns of AAESS δ13C
values, or ‘fingerprints’, of the food resources available to corals. This
allowed for the development of a quantitative continuum of coral nutrition
that can identify the relative contribution of autotrophic and heterotopic
nutrition to individual colonies. Our approach revealed exceptional
variation in conspecific colonies at scales of meters to kilometers. On
average, 41% of AAESS in P. meandrina on Palmyra are acquired via
heterotrophy but some colonies appear capable of obtaining the majority of
AAESS from one source or the other. 5. The use of AAESS δ13C
fingerprinting analysis offers a significant improvement on the current
methods for quantitatively assessing coral trophic ecology. We anticipate
that this approach will facilitate studies of coral nutrition in the
field, which are essential for comparing coral trophic ecology across taxa
and multiple spatial scales. Such information will be critical for
understanding the role of heterotrophic nutrition in coral resistance
and/or resilience to ongoing environmental change.