Keep up or drown: adjustment of western Pacific coral reefs to sea-level rise in the 21st century

Abstract

Since the Mid-Holocene, some 5000 years ago, coral reefs in the Pacific Ocean have been vertically constrained by sea level. Contemporary sea-level rise is releasing these constraints, providing accommodation space for vertical reef expansion. Here, we show that Porites microatolls, from reef-flat environments in Palau (western Pacific Ocean), are ‘keeping up’ with contemporary sea-level rise. Measurements of 570 reef-flat Porites microatolls at 10 locations around Palau revealed recent vertical skeletal extension (78±13 mm) over the last 6–8 years, which is consistent with the timing of the recent increase in sea level. We modelled whether microatoll growth rates will potentially ‘keep up’ with predicted sea-level rise in the near future, based upon average growth, and assuming a decline in growth for every 1°C increase in temperature. We then compared these estimated extension rates with rates of sea-level rise under four Representative Concentration Pathways (RCPs). Our model suggests that under low–mid RCP scenarios, reef-coral growth will keep up with sea-level rise, but if greenhouse gas concentrations exceed 670 ppm atmospheric CO2 levels and with +2.2°C sea-surface temperature by 2100 (RCP 6.0 W m−2), our predictions indicate that Porites microatolls will be unable to keep up with projected rates of sea-level rise in the twenty-first century.

Paradise lost: End‐of‐century warming and acidification under business‐as‐usual emissions have severe consequences for symbiotic corals

“…In bleached A. intermedia , G TA was negative, despite average seawater Ω ARAG values of 3.39 (Table ) and daytime G TA was not reduced in either species as long as photosynthetic rates were maintained (Levas et al, ). The constraints of elevated temperature and acidification on long‐ and short‐term measures of skeleton growth will, provided that corals survive, limit reef capacity to outpace sea‐level rise and decrease resilience to extreme weather (Manzello et al, ; Mollica et al, ; van Woesik et al, ).…”

“…Despite recent success in stabilizing the global increase in GHG emissions between 2014 and 2016 (1.8% had dropped to 0.4% increase per year), GHG emission rates are currently back at 2007-2013 levels (Jackson et al, 2017;Le Quéré et al, 2018;Peters et al, 2017) and tracking the high emission, "business-as-usual" representative concentration pathway (RCP) 8.5 scenario. Irrespective of our efforts to curtail GHG emissions, the lagging persistence of CO 2 in the atmosphere will cause increased frequency and intensity of heat stress over the coming decades (Hoegh-Guldberg et al, 2014), and reefs worldwide will likely start experiencing annual bleaching outside of El Niño years (van Hooidonk et al, 2016).…”

“…The number of studies investigating the individual and combined effects of temperature and pCO 2 in an orthogonal design has steadily increased in recent years (Büscher, Form, & Riebesell, 2017;Edmunds et al, 2012;Reynaud et al, 2003;Schoepf et al, 2013). However, not many orthogonal studies address extreme warming and acidification conditions (Hoadley et al, 2016) such as under the RCP8.5 emission scenario, which predicts a rise of approximately +3.5°C and +570 µatm CO 2 for non-El Niño years by 2100 compared to present-day (PD) levels (Meinshausen et al, 2011;van Vuuren et al, 2011). Importantly, most studies employed static elevations of temperature and CO 2 , thereby losing the diel and seasonal environmental cycles and variability of a natural system.…”

Building the future of MPAs – lessons from history

“…The assumption is that by reducing or eliminating stressors (such as over‐harvesting or pollution), the species and habitats within MPAs will be more resilient. The ecological principle of ‘resilience’ refers to communities that are able to bounce back or recover after experiencing a stressful event such as coral bleaching (Shamberger et al ., ), or that are able to keep pace with sea‐level rise (van Woesik et al ., ). If such resilient locations can be identified, it would be possible to consider reconfiguring MPAs to include them, according to the nature of the stress involved.…”

Coral Reefs Under Climate Change and Ocean Acidification: Challenges and Opportunities for Management and Policy

“…Importantly, other consequences of severe climate change, such as changing ocean circulation and sea level rise, may also have significant impacts on coral reefs (9). Specifically, modern coral reefs are keeping up with current sea level rise and may continue to do so under RCP2.6 and RCP4.5 (50). However, risks of rapid sea level rise in combination with suppressed net rates of coral calcification due to warming and acidification under the RCP8.5 scenario might see some coral reefs drowning in a high-CO 2 world.…”