[Coral-List] Reef Islands & Sea Level

Dennis Hubbard dennis.hubbard at oberlin.edu
Tue Sep 16 13:58:59 EDT 2014

Many of you probably remember a post in which a recent popular article in
*Science* argued that reef islands will be able to track rising sea level
because of the rapid rates of reef accretion(10-15 mm/yr) and the stability
of island-area measurements on several atolls. Further, the article argued
that the blame lay as much at the feet of the islanders who have made bad
decisions as it does with anything else.

 In a reply to the list, I invited anyone that took exception to this
article to contact me offline. The following was written jointly by 15 of
us and submitted as a letter to Science. It was accepted and will appear in
the next issue (there may be a couple of very minor differences as we have
been editing this right up to the end). I want to thank the 14 colleagues
who participated in this process (I learned a lot from them) and I hope
that this may stimulate some productive discussions about differences
between coral growth and reef building.... and how understanding the
complex issues of island survival going forward involves complex
interactions of biology, geology/geography, physical oceanography, social
(both present and past) and myriad other factors that don't relate to
simply counting coral losses.

 The Supplemental materials are in the article but I can email them to
anyone who is interested.

 *Will Islands Build in Step With a Rising Sea? *

In his In Depth news story “Warming may not swamp islands” (1 August, p.
496), C.. Pala argues that "coral reefs supporting sandy atolls will grow
in tandem with the sea," based largely on studies that showed stable
Pacific-island area over recent decades (*1*–*4*). He suggests that recent
land losses are driven mostly by bad choices and that islanders are being
affected "for the same reason as millions of people on the continents:
because they live too close to the shore". We disagree with these

Pala bases his arguments on evidence that (i) reefs can build vertically at
10 to 15 mm/year, a rate far exceeding the anticipated rate of sea-level
rise and (ii) sequential air photographs document stable island areas
despite rising sea level. An analysis of the early literature (i.e.,
pre-1999, when the article stated that no relevant data existed) revealed
22 articles reporting much lower reef-accretion rates—0.60 to 7.89 mm/year,
averaging 3.54 (see supplementary materials). More recent reviews similarly
conclude that rates of 10 to 15 mm/year are much too high for Holocene reef
building (*5*–*8*). Recent declines in coral cover can only slow accretion
in the future.

Naomi Biribo has noted that "widespread erosion along the ocean and lagoon
shorelines is primarily due to human activities" (*3*). However, the same
paper also attributes 90% of the increase in island area on South Tarawa to
reclamation projects (i.e., no inherent ability to keep pace with sea level
naturally). Island area may not provide an adequate measure of either
changing sediment volume or the susceptibility of the island to flooding,
erosion, or drowning. It is possible that erosion of sand from higher
marginal areas and redistribution to lower shorelines elsewhere on the
island can increase island area even in the face of declining sediment

Pala's sources describe islands building seaward 4800 - 4500 years ago (*3*,
*9*), a pattern opposite to the island retreat that is occurring today. If
rising sea level is to be discounted, then a mechanism to explain this
recent reversal must be identified. Also, fewer corals making calcium
carbonate and stronger storms removing at least some of it can only reduce
sediment availability.

We also take exception to laying the sole blame at the feet of islanders
who have occupied these fragile islands for millennia. Human communities
living on atoll islets often depend on thin aquifers, agro-forestry, and
freshwater wetland taro production. Saltwater intrusion and flooding
destroys otherwise sustainable food and water sources (*10*), making
islands unlivable long before drowning.

Certainly the situation has been exacerbated by poor choices, and politics
is rarely the best lens for viewing natural phenomena. Adapting to either
sea-level rise or more frequent inundation often involves ill-placed
engineering solutions that require substantial volumes of sand and rock
that would be better left in place to protect coastlines and contribute to
island sediment budgets. The meteorological instability that comes with
rising temperatures, the likely increase in erosion and storm surge,
islands constantly retreating from the sea, dwindling ground-water
supplies, decreasing rainfall... and rising sea level will all have
disproportionate impacts on populations that are least responsible for
global carbon emissions that are at the heart of these changes.

Dennis Hubbard,1* Eberhard Gischler,2 Peter Davies,3 Lucien Montaggioni,4
Gilbert Camoin,5 Wolf-Christian Dullo,6 Curt Storlazzi,7 Michael Field7
Charles Fletcher,9 Eric Grossman,10 Charles Sheppard,11 Halard Lescinsky,12
Douglas Fenner,13 John McManus,14 Sander Scheffers15

1Department of Geology, Oberlin College, Oberlin, OH 44074, USA. 2Institut
fuer Geowissenschaften, Goethe-Universitaet, 60438, Frankfurt am Main,
Germany. 3School of Geoscience, University of Sydney, Sydney, NSW 2006,
Australia. 4Aix-Marseille University, CEREGE, UMR 7330 CNRS, Centre
Saint-Charles, 13331, Marseille, France. 5Aix-Marseille University, CEREGE,
UMR 7330 CNRS, F-13545, Aix-en-Provence, France. 6FB1 Ozeanzirkulation und
Klimadynamik, GEOMAR, Helmholtz-Zentrum für Ozeanforschung Kiel, 24148,
Kiel, Germany. 7U.S. Geological Survey, Pacific Coastal and Marine Science
Center, Santa Cruz, CA 95060, USA. 9University of Hawaii, School of Ocean
and Earth Science and Technology, Honolulu, HI 96822, USA. 10U.S.
Geological Survey,  Western Fisheries Research Center, Seattle, WA 98115,
USA. 11School of Life Sciences, University of Warwick, Coventry, CV4 7AL,
UK. 12Department of Biology and Earth Sciences, Otterbein University,
OH 43081, USA. *13Ocean Associates, Pago Pago, AS 96799, USA. 14National
Center for Coral Reef Research, Rosenstiel School of Marine and Atmospheric
Science, University of Miami, Miami, FL 33149, USA. 15School of
Environment, Science and Engineering, Southern Cross University, Lismore,
NSW 2480, Australia.

*Corresponding author. E-mail: dennis.hubbard at oberlin.edu


1. A. P. Webb, P. S. Kench, *Glob. Plan. Change* *72*, 234 (2010).

2. M. Ford, *J. Coast. Res.* *28*, 11 (2012).

3. N. Biribo, C. D. Woodroffe, *Sustain. Sci.* *8*, 345 (2013).

4. P. S. Kench, S. D. Owen, M. R. Ford, *Geophys. Res.. Lett.*
10.1002/2013GL059000 (2014).

5.. P. J. Davies, D. Hopley, *BMR J. Australian Geol. Geophys.* *8*, 237

6. L. Montaggioni, *5th Intl. Coral Reef Symp.* *3*, 455 (1998).

7. W.-C. Dullo, *Facies* *51*, 33 (2005).

8. D. K. Hubbard, in *Perspectives in Carbonate Geology*, P. J. Swart, G.
Eberli, J. McKenzie, Eds. (Wiley-Blackwell, West Sussex, UK, 2009), pp.

9. W. R. Dickinson, *GSA Today* *19*, 4 (2009).

10. C. H. Fletcher, B. M. Richmond, “Climate change in the Federated States
of Micronesia: Food and water security, climate risk management, and
adaptive strategies” (Report of Findings, Sea Grant College of Hawaii,

Supplementary Materials

References (*11*–*32*)

Dennis Hubbard
Chair, Dept of Geology-Oberlin College Oberlin OH 44074
(440) 775-8346

* "When you get on the wrong train.... every stop is the wrong stop"*
 Benjamin Stein: "*Ludes, A Ballad of the Drug and the Dream*"

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