title: Do clouds save the great barrier reef? satellite imagery elucidates the cloud-SST relationship at the local scale.
abstract: Evidence of global climate change and rising sea surface temperatures (SSTs) is now well documented in the scientific literature. With corals already living close to their thermal maxima, increases in SSTs are of great concern for the survival of coral reefs. Cloud feedback processes may have the potential to constrain SSTs, serving to enforce an "ocean thermostat" and promoting the survival of coral reefs. In this study, it was hypothesized that cloud cover can affect summer SSTs in the tropics. Detailed direct and lagged relationships between cloud cover and SST across the central Great Barrier Reef (GBR) shelf were investigated using data from satellite imagery and in situ temperature and light loggers during two relatively hot summers (2005 and 2006) and two relatively cool summers (2007 and 2008). Across all study summers and shelf positions, SSTs exhibited distinct drops during periods of high cloud cover, and conversely, SST increases during periods of low cloud cover, with a three-day temporal lag between a change in cloud cover and a subsequent change in SST. Cloud cover alone was responsible for up to 32.1% of the variation in SSTs three days later. The relationship was strongest in both El Niño (2005) and La Niña (2008) study summers and at the inner-shelf position in those summers. SST effects on subsequent cloud cover were weaker and more variable among study summers, with rising SSTs explaining up to 21.6% of the increase in cloud cover three days later. This work quantifies the often observed cloud cooling effect on coral reefs. It highlights the importance of incorporating local-scale processes into bleaching forecasting models, and encourages the use of remote sensing imagery to value-add to coral bleaching field studies and to more accurately predict risks to coral reefs.
authors.affiliation: School of Marine and Tropical Biology, James Cook University, Townsville, Queensland, Australia. Susannah.Leahy@my.jcu.edu.au
authors.forename: Susannah M
authors.initials: SM
authors.lastname: Leahy
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Kingsford
authors.forename: Craig R
authors.initials: CR
authors.lastname: Steinberg
mesh_terms: D000704:Analysis of Variance; D057231:Climate Change; D057894:Coral Reefs; D013696:Temperature
references.citation: Mar Pollut Bull. 2009 Oct;58(10):1428-36
references.pmid: 19782832
references.citation: Curr Biol. 2009 Jul 28;19(14):R602-14
references.pmid: 19640499
references.citation: Science. 2007 Dec 14;318(5857):1737-42
references.pmid: 18079392
references.citation: Mar Pollut Bull. 2002 Dec;44(12):1380-7
references.pmid: 12523543
references.citation: Science. 2007 Jan 26;315(5811):506-8
references.pmid: 17255509
references.citation: Science. 2005 Jul 8;309(5732):284-7
references.pmid: 15933161
references.citation: Adv Mar Biol. 2003;46:183-223
references.pmid: 14601413
references.citation: J Exp Biol. 2008 Apr;211(Pt 7):1050-6
references.pmid: 18344478
references.citation: Australas J Dermatol. 1979 Aug;20(2):68-74
references.pmid: 533500