Country-level dependence on coral reef ecosystem services and future risk of coral bleaching.

<p>Bleaching risk is indicated by the year when DHW8 is first reached annually, under RCP8.5 scenario [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164699#pone.0164699.ref024" target="_blank">24</a>,<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0164699#pone.0164699.ref025" target="_blank">25</a>]. Ocean Provinces are indicated in each panel in bold. Earlier years indicate increased bleaching risk.</p

Regional dependence, by ocean province [49], on ecosystem services and average CO₂-related threats (ocean acidification measured as projected Ω_ar levels at coral reefs in 2050 and elevated sea surface temperature as measured by year that 8 DHW are projected to occur annually).

<p>The horizontal line in the threats panel represents the mean threat for all regions (scores above this line indicate above average severity of threat). The scales for the reef fish dependence scores are broken to reduce the size of the graph. Note that the Great Barrier Reef Ocean Province includes, but is not limited to, the Great Barrier Reef.</p

Scores of human dependence on coral reef ecosystem services, by country.

<p>Panel A provides the normalized scores for human dependence on shoreline protection, Panel B shows the normalized scores for dependence on reef fisheries, and Panel C shows combined human dependence. All scores are normalized on a scale from 0–10. Higher scores reflect higher human dependence. Countries are binned by quintile in the legend.</p

A conceptual diagram linking stresses related to increased atmospheric CO₂ (elevated sea surface temperature and ocean acidification), storms, and local stressors to coral reef condition, selected ecosystem services provided by reefs, and human dependence on these ecosystem services.

<p>Solid lines represent relationships evaluated in this study.</p

Raw data and results of the normalized scoring for human dependence, by country (only countries for which data are available are shown).

<p>Ocean Provinces: Brazilian (B), Caribbean (C), Central Pacific (CP), Great Barrier Reef (GBR), Central Indian Ocean (CIO), Eastern Pacific (EP), Middle East (ME), Polynesia (P), South East Asia (SEA), Western Australia (WA), Western Indian Ocean (WIO).</p

Country-level dependence on coral reef ecosystem services and future combined normalized scores (2–20) for CO₂-related threats (e.g. ocean acidification and thermal stress).

<p>Ocean Provinces are indicated in each panel in bold. Higher scores indicate higher dependence and higher ecological risk.</p

Taking the metabolic pulse of the world’s coral reefs

<div><p>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.</p></div

Net calcification potential measured as anomalies between open ocean and coral reef TA concentrations (ΔTA) at each location.

<p>Negative values are lower TA concentrations within the reef and represent net CaCO₃ precipitation (+NCC), while positive values are higher TA concentrations within the reef and represent net CaCO₃ dissolution (-NCC). Edges of the box are the 25^th and 75^th percentiles, the line within each box is the median, the whiskers represent the most extreme data points that are not outliers, and the red + symbols are outliers.</p

Seawater TA and DIC data from 23 coral reef locations around the world in increasing order of TA-DIC slope.

<p>The black line is the Type II linear regression of the data. Red lines are pH isolines at 0.1 units increments with the 8.0 pH isoline indicated for reference. pH contours were calculated using the average seawater temperature and salinity of each dataset. The blue dashed line in each panel is the approximate TA of the offshore seawater determined as described in the text.</p

The dominant metabolic processes on coral reefs and their influence on seawater total alkalinity (TA), dissolved inorganic carbon (DIC), and pH.

<p>(A) The organic carbon cycle (NCP) is dominated by photosynthesis and respiration, which take up or release 1 mole of DIC for every mole of organic carbon (CH₂O) produced or decomposed with little influence on seawater TA. In contrast, the inorganic carbon cycle (NCC) is dominated by CaCO₃ precipitation and dissolution, which alter TA and DIC in a ratio of 2:1 for every mole of CaCO₃ precipitated or dissolved. Photo credit: Yuna Zayasu, OIST. (B) Depending on the relative contribution from different metabolic processes, the resulting change in TA and DIC influences seawater pH differently (colored contours). Photosynthesis and CaCO₃ dissolution increase seawater pH while respiration and CaCO₃ precipitation decrease pH. If NCP and NCC are closely balanced (i.e., TA-DIC slope ~1), there is little change in seawater pH owing to net reef metabolism. This is because the slope of pH isolines within the normal oceanic concentration of seawater TA and DIC are close to 1. Therefore, when the slope of the TA-DIC vector is different from 1 the pH isolines are crossed and seawater pH can be altered considerably. The calculations for pH at each TA and DIC value assume constant temperature (25°C) and salinity (35). (C) Conceptual schematic of the biogeochemical and metabolic function of coral reefs. Net CaCO₃ precipitation (+NCC, green area) vs. net dissolution (-NCC, pink/red area); net autotrophy (+NCP) vs. net heterotrophy (-NCP), and different TA-DIC slopes, as well as the resulting changes in reef seawater pH (pH_r) relative to the open ocean (pH_o) under constant salinity and temperature conditions.</p