Temperature and light patterns at four reefs along the Great Barrier Reef during the 2015–2016 austral summer: understanding patterns of observed coral bleaching

Abstract

Data from real-time sensor networks along the Great Barrier Reef (GBR) over the 2015-2016 austral summer showed that reef water temperatures exceeded empirical coral bleaching thresholds at a number of sites. Temperatures in the southern GBR were within historically normal limits with temperatures below the empirical bleaching threshold. The central GBR just reached the empirical bleaching threshold while, in the north, Lizard Island recorded four consecutive days above the bleaching threshold. Thursday Island in the far northern GBR experienced 10 days above the bleaching threshold. The in situ data predicted only slight bleaching in the southern GBR, moderate bleaching in the central GBR, widespread bleaching in the north and severe bleaching in the far north, which compares well with the initial survey data. Peak temperatures occurred later in the year in the north (mid-March 2016) than in the south (early February 2015) with temperatures remaining above the long-term mean well into the austral autumn. Comparison against satellite sea surface temperature data highlighted issues of cloud cover with data only being available for 30-40% of days over the summer. While the agreement with the in situ data was good, the satellite data missed fine-scale events and underestimated the event at Thursday Island.

Dimethylsulfide (DMS), marine biogenic aerosols and the ecophysiology of coral reefs

“…Ocean warming is considered to be one of the greatest threats to coral reefs (Baker et al, 2008;Hughes et al, 2018;Skirving et al, 2019). More than 90% of the heat energy accumulated in the Earth's climate system, largely a result of anthropogenic greenhouse gas (GHG) emissions, is stored in the ocean.…”

“…SST greater than ∼ 2 • C above the summertime maximum can result in coral bleaching over much shorter timescales, depending on coral tolerance to thermal and/or irradiance stress and on the magnitude and duration of exposure (Bainbridge, 2017). If stress levels subside quickly, corals may regain their zooxanthellae and recover, although surviving corals can have reduced growth, calcification and reproductive rates and a higher incidence of disease and competitive susceptibility (Baker et al, 2008;Ward et al, 2002;Chaves-Fonnegra et al, 2018). Recent work found an 89 % decline in larval recruitment during the 2018 spawning event in the GBR after consecutive mass bleaching events adversely affected populations of adult spawning corals (Hughes et al, 2019).…”

Reviews and syntheses: Marine biogenic aerosols and the ecophysiology of coral reefs

“…As many Scleractinian corals now reside in regions with SST close to their upper physiological limits, a 0.5º C rise in SST above the local summer maximum for a period of several weeks is sufficient to cause coral bleaching and mortality (Berkelmans, 2009). SST greater than ~2º C above the summertime maximum can result in coral bleaching over much shorter time-scales (Bainbridge, 2017). If stress levels subside quickly, corals may regain their zooxanthellae and recover, although surviving corals can have reduced growth, calcification and reproductive rates and a higher incidence of disease and competitive susceptibility (Baker et al, 2008;Ward et al, 2002;Chaves-Fonnegra et al, 2018).…”

“…Empirical evidence has demonstrated that DHW of 8° C-weeks reliably predicts mass coral bleaching and mortality (Liu et al, 2003). This is the most widely used measure for assessing and predicting coral bleaching events (Hughes et al, 2018;Bainbridge, 2017;Berkelmans, 2009 ;Skirving et al, 2019). The NOAA Coral Reef Watch is also producing a Light Stress Damage (LSD) measure which incorporates coral light stress as a contributor to coral bleaching, based on PAR anomalies (Skirving et al, 2017).…”

“…Additionally, validation of these products requires in situ observations (e.g. Bainbridge, 2017). Therefore, a multidisciplinary approach which utilises both field and remote sensing observations in conjunction with earth system models, is needed to improve our understanding of the biogeochemical processes occurring in coral reefs and the ways we can effectively ensure their preservation.…”