Taking the metabolic pulse of the world’s coral reefs
Résumé
Worldwide, coral reef ecosystems are experiencing increasing pressure from a variety of
anthropogenic perturbations including ocean warming and acidification, increased sedimentation,
eutrophication, and overfishing, which could shift reefs to a condition of net calcium
carbonate (CaCO3) dissolution and erosion. Herein, we determine the net calcification
potential and the relative balance of net organic carbon metabolism (net community production;
NCP) and net inorganic carbon metabolism (net community calcification; NCC) within
23 coral reef locations across the globe. In light of these results, we consider the suitability
of using these two metrics developed from total alkalinity (TA) and dissolved inorganic carbon
(DIC) measurements collected on different spatiotemporal scales to monitor coral reef
biogeochemistry under anthropogenic change. All reefs in this study were net calcifying for
the majority of observations as inferred from alkalinity depletion relative to offshore, although occasional observations of net dissolution occurred at most locations. However,
reefs with lower net calcification potential (i.e., lower TA depletion) could shift towards net
dissolution sooner than reefs with a higher potential. The percent influence of organic carbon
fluxes on total changes in dissolved inorganic carbon (DIC) (i.e., NCP compared to the
sum of NCP and NCC) ranged from 32% to 88% and reflected inherent biogeochemical differences
between reefs. Reefs with the largest relative percentage of NCP experienced the
largest variability in seawater pH for a given change in DIC, which is directly related to the
reefs ability to elevate or suppress local pH relative to the open ocean. This work highlights
the value of measuring coral reef carbonate chemistry when evaluating their susceptibility to
ongoing global environmental change and offers a baseline from which to guide future conservation
efforts aimed at preserving these valuable ecosystems.
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