Volume 16, Number 32: 7 August 2013
In a paper published earlier this year in Nature Climate Change, Wiedenmann et al. (2013) note that mass coral bleaching "has been identified as the most severe threat to coral reef survival on a global scale," citing Hughes et al. (2003); but they indicate that regionally "nutrient enrichment of reef waters is often associated with a significant loss of coral cover and diversity," citing the work of Fabricius (2005). In addition, and citing Wooldridge (2009), they also state that more recently, "increased dissolved inorganic nitrogen concentrations have been linked to a reduction of the temperature threshold of coral bleaching."
In a series of experiments designed to explore this subject in greater detail, the seven scientists formulated "a new conceptual model of nutrient effects on coral bleaching," wherein "the most severe impact on coral health might actually not arise from the over-enrichment with one group of nutrients (for example, dissolved inorganic nitrogen) but from the resulting relative depletion of other types (for example, phosphate) that is caused by the increased demand of proliferating zooxanthellae populations," which view "is substantiated by the finding that the photosynthetic efficiency of zooxanthellae is reduced under a combination of limited iron availability and high temperatures," as per the work of Shick et al. (2011).
"This model," as Wiedenmann et al. go on to discuss it, "improves the understanding of the detrimental effects of coastal nutrient enrichment on coral reefs, which is urgently required to support knowledge-based management strategies to mitigate the effects of climate change." More specifically, they write that "reef resilience could benefit from considering local nutrient profiles and adjusting agricultural and tertiary wastewater-treatment practices in the proximity of coral reefs to reach favorable nutrient ratios in reef waters while working towards overall lower nutrient loadings."
And finally, as they put it, they make a point of stating that their findings "support the view that local management of nutrient enrichment could reduce the effects of global climate change on coral reefs," which has long been our view as well.
Sherwood, Keith and Craig Idso
References
Fabricius, K.E. 2005. Effects of terrestrial runoff on the ecology of corals and coral reefs: review and synthesis. Marine Pollution Bulletin 50: 125-146.
Hughes, T.P., Baird, A.H., Bellwood, D.R., Card, M., Connolly, S.R., Folke, C., Grosberg, R., Hoegh-Guldberg, O., Jackson, J.B.C., Kleypas, J., Lough, J.M., Marshall, P., Nystrom, M., Palumbi, S.R., Pandolfi, J.M., Rosen, B. and Roughgarden, J. 2003. Climate change, human impacts, and the resilience of coral reefs. Science 301: 929-933.
Shick, J.M., Iglic, K., Wells, C.G., Trick, J.D. and Dunlap, W.C. 2011. Responses to iron limitation in two colonies of Stylophora pistillata exposed to high temperature: Implications for coral bleaching. Limnology and Oceanography 56: 813-828.
Wiedenmann, J., D'Angelo, C., Smith, E.G., Hunt, A.N., Legiret, F.-E., Postle, A.D. and Achterberg, E.P. 2013. Nutrient enrichment can increase the susceptibility of reef corals to bleaching. Nature Climate Change 3: 160-164.
Wooldridge, S.A. 2009. Water quality and coral bleaching thresholds: Formalizing the linkage for the inshore reefs of the Great Barrier Reef, Australia. Marine Pollution Bulletin 58: 745-751.