Coral reef calcification and production after the 2016 bleaching event at Lizard Island, Great Barrier Reef

Severe coral bleaching events have affected the Great Barrier Reef (GBR) causing massive losses of hard coral cover. Here, we use flow respirometry approaches to assess coral reef net ecosystem calcification (NEC) and net ecosystem production (NEP) following the 2015/2016 bleaching event at Lizard Island in the northern GBR, a heavily impacted area. Previous studies conducted in 2008 and 2009 [Silverman et al., 2014] were used as pre‐impact data. Lagrangian and Eulerian approaches provided varied results. Estimated NEC (29.1 – 137.7 mmol m‐2 day‐1) and NEP (‐876.7 – 50.5 mmol m‐2 day‐1) rates in 2016 were highly sensitive to assumptions about reef water residence times and oceanic endmember concentrations. Replicating the methodology used for the 2008 and 2009 study resulted in post‐bleaching NEC in 2016 at 32 ± 10.8 mmol m‐2 day‐1, 40 – 46% lower than pre‐bleaching estimates in 2008 (61 ± 12 mmol m‐2 day‐1) and 2009 (54 ± 13 mmol m‐2 day‐1). The slopes of a total alkalinity vs. dissolved inorganic carbon (TA – DIC) plot decreased from ~ 0.3 in 2008 and 2009 to 0.1 in 2016, indicating elevated organic production and a shift in community function. Changes in NEC relative to the previous study were not driven by changing Ω arag. Coral cover shifted from 8.3% and 7.1% in 2008 and 2009 to 3.0% in 2016. We demonstrate a clear decrease in coral reef NEC following bleaching and highlight that subtle assumptions/methodological differences may create bias in the interpretation of results. Therefore, comparing coral reef metabolism datasets and predicting long‐term coral reef calcification based on existing short‐term datasets needs to be done with care.

McMahon A., Santos I. R., Schulz K. G., Scott A., Silverman J., Davis K. L. & Maher D. T., in press. Coral reef calcification and production after the 2016 bleaching event at Lizard Island, Great Barrier Reef. JGR Oceans. Article (subscription required).

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