Abstract
Climate change is threatening the persistence of coral reef ecosystems resulting in both chronic and acute impacts which include higher frequency and severity of cyclones, warming sea surface temperatures, and ocean acidification. This study measured net ecosystem primary production (NEP) and net ecosystem calcification (NEC) on a reef flat after the most severe El Nino-driven mass bleaching event on Australia’s Great Barrier Reef (GBR) in 2016 and again in 2018 after another consecutive bleaching event in 2017. Our results indicate that reef metabolism is altered as result of both the continuing press disturbance of ocean acidification and severe pulse disturbances (cyclones and bleaching events). In 2016, NEP was within the range of values reported in past studies, however it declined in 2018. NEC over a 12-h period was lower in 2016 than 2018; but when compared with past studies there was a severe decline in daytime net calcification from 2008-2009, to 2016 followed by an increase in 2018 (but still NEC remained lower than values reported in 2008-2009). Conversely, nighttime net calcification was similar to that reported in 2009 indicating nighttime dissolution did not increase over the past decade. Overall coral cover remained stable following recent disturbances, however algal turf was the dominant benthic component on the reef flat, while calcifiers (corals and calcified algae) were minor components (< 20% of total benthic cover). This study documented changes in community function following major pulse disturbances (bleaching events and cyclones) within the context of ongoing OA at the same location over the last decade. Repeated pulse disturbances could jeopardize the persistence of the reef flat as a net calcifying entity, with the potential for cascading effects on other ecosystem services.
Highlights
Coral reefs are highly dynamic ecosystems that have developed under a wide range of disturbances operating at different spatial and temporal scales (Nyström and Folke, 2001)
net ecosystem primary production (NEP)/net ecosystem calcification (NEC) typically are measured over sections (100 s of meters) of reefs (Kinsey, 1979; Barnes, 1983; Odum and Odum, 1955), thereby integrating specific community structure/function relationships over a larger scale
While NEP/NEC have been quantified at a diversity of coral reef locations (Kinsey, 1979; Shamberger et al, 2011; Albright et al, 2015; Takeshita et al, 2016), repeated measurements over time at a single location are rare
Summary
Coral reefs are highly dynamic ecosystems that have developed under a wide range of disturbances operating at different spatial and temporal scales (Nyström and Folke, 2001). Positive NEC indicates that the biogenic structure is accreting calcium carbonate and that calcifying organisms such as foraminifera, calcareous algae and reef-building scleractinian corals, are producing CaCO3 faster than the physical, chemical, and bioerosive processes are removing it, maintaining reef accretion and growth. The majority of studies have investigated species-specific responses to bleaching and/or ocean acidification (Cooper et al, 2008; De’ath et al, 2009; Comeau et al, 2013, 2016), but see (Dove et al, 2013; Silverman et al, 2014) and have demonstrated that some species are more susceptible to bleaching than others and that effects of pCO2 on calcification is species-specific (Comeau et al, 2013) with the subsequent consequences at community and ecosystem levels dependent on the relative abundances of sensitive and less sensitive taxa (Dove et al, 2013). We expected to find a decline in NEC due to reduced live coral cover, while we predicted that NEP would increase due to more abundant benthic algae which often increase in biomass and percent cover following high coral mortality (Hughes et al, 2007)
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call