[Coral-List] Are atolls doomed or can atolls grow as fast as sea level rise?

Tue Jan 2 20:21:12 UTC 2024

Thanks to Doug for the reference and to Bob for the perspective!

I work with coral reefs in the atoll nations of Kiribati and Tuvalu.  Both
governments are looking into raising their land areas via suction dredging,
and some extensive work has already happened, and much more is planned.
Tuvalu is now using big geotextile bags to form sand filled pillows for the
retention edges- while before they brought big volcanic rocks from Fiji,
which was ridiculously expensive.  Suction dredges can do amazing work very
fast and there are heaps of fine sand in the lagoons-  all they need is 2-3
big dredges going all the time on each atoll. They can create big hills
10-20m high on intertidal backreef areas with amazing speed.  But of course
this costs money, and there are many outer islands needing this work done.

An unfortunate condition has arisen in the death of these reefs. Kiribati
(pronounced Kiribas- ti is pronounced as an s), has experienced some of the
most intense marine heat waves anywhere, and  formerly Acropora dominated
coral reefs are now either being dominated by dead rock, with scattered
Pocillopora and Porites and other slower growing species, or replaced by
high coral cover of an alternate Porites rus dominated system, which of
course grows much slower and produces less carbonate than the former
system, not to mention an altered habitat for fish and inverts. Accretion
rates are now obviously much slower than in the past, or even negative for
some areas, as parrotfish chew away at the coral skeletons on the reef
flats- all the way down to the hard calcitic of the former low sea level
stand.   Unfortunately ciguatera has also become dominant among the reef
fish populations, subsequent to the coral die-off.   Once Acropora becomes
rare, it becomes the target of voracious parrotfish and butterflyfish,
which can chew it into oblivion. Pocillopora is clearly more resilient to
these bites. Gathering Acropora survivors into nurseries located away from
dense populations of these two fish species can help secure the corals and
increase their growth.

In stark contrast to Kiribati, Tuvalu has the most spectacular populations
of Acropora corals I have ever seen, with huge thickets of heavy branched
staghorn species, never having had a mass coral die off, and with no severe
bleaching recorded to date, with no COTS outbreaks, nor any severe
cyclones.  However this is now coming to an end, as the marine heat wave
has arrived.  The open ocean around Tuvalu is holding at 31C, with the
lagoons much hotter.  Not much will be left by the time the waters cool
down in May.  There is a report from a few years back indicating via
satellite images, that Tuvalu is growing in response to SLR. The rubble and
sand is apparently mobilizing and moving shoreward during high wave events,
with overtopping waves sometimes depositing sand and rubble onto the
roads.  The airport was closed just two weeks ago due to seawater damage to
the tarmac incurred during a king tide.  Sadly, the death of most of the
corals of Tuvalu may change its prospects for natural adaptation as
accretion rates will be altered considerably.

While it would be impossible to replant these extensive atolls, and as
there may not be much coral left, we have begun pilot work to at least
secure some of the most heat adapted individuals, by moving them out of the
hottest lagoon areas and into cooler reef areas.  We will also be
collecting samples of unbleached corals towards the end of the mass
bleaching event.  Our aim is to reboot sexual reproduction within patches
of corals located in cooler upcurrent reef areas, so that coral larvae
become more abundant in the lagoon, encouraging natural recovery processes.
This is our plan for assisted adaptation, and if it helps these coral reefs
retain their coral diversity and results in higher accretion rates over
time, only time will tell.

Regards,

Austin

Austin Bowden-Kerby, PhD
Corals for Conservation
P.O. Box 4649 Samabula, Fiji Islands

https://www.corals4conservation.org
Publication on C4C's coral-focused climate change adaptation strategies:
https://www.mdpi.com/2673-1924/4/1/2/pdf
Film on our "Reefs of Hope" coral restoration for climate change adaptation
strategies:  https://www.youtube.com/watch?v=BG0lqKciXAA
https://www.globalgiving.org/projects/emergency-response-to-massive-coral-bleaching/
<https://www.globalgiving.org/projects/emergency-response-to-massive-coral-bleaching/>

On Thu, Dec 28, 2023 at 3:06 AM Robert W Buddemeier via Coral-List <
coral-list at coral.aoml.noaa.gov> wrote:

> *Re:  Atoll resilience in the face of rising sea level*
>
>
>
> The article on this topic referenced by Doug Fenner fails to address some
> significant considerations.
>
> It may be true that atolls as landforms will accrete at a rate comparable
> to sea level rise (SLR). That does not mean that the accretion process will
> support continued human habitation, which I think is the real concern.
>
> Humans live on the supratidal surface of the atoll – which must also be
> high enough or protected enough to sustain infrastructure, agriculture, and
> water resources.
>
> In order to maintain the necessary elevation above sea (or high tide)
> level, new sediment must be deposited on top of the existing surface, and
> reasonably uniformly distributed across the usable area.
>
> Since sediment is produced subtidally, a substantial amount of energy is
> required to lift it onto and distribute it over the atoll surface.
> Realistically, this means a major storm surge, large enough to wash over
> most of the island surface and carry a lot of sediment with it.
>
> Overwash by high energy, sediment-bearing salt water will damage or destroy
> structures, contaminate soil and groundwater, and kill or damage all but a
> few types of vegetation.  Recovery is unlikely to occur on a time scale
> consistent with continued or immediate human habitation.
>
> Even if that were not the case there is another major concern.  Sea level
> rise is continuous, whereas major atoll-building storms are highly episodic
> – and rarely occur in some locations.  Current SLR is 0.12-0.14 inches per
> year, and expected to increase. I think that the return interval for
> overwash events is well in excess of a century for most atolls.  For atoll
> inhabitants, it looks like a choice between slow displacement and rapid
> devastation, with no very good idea of the time constants for either.
>
> Advancing the idea that atolls, *as human habitations*, can naturally keep
> up with sea level rise risks allowing governments to assume that there
> needs to be no provision of rescue or refuge for current and future atoll
> dwellers.
>
> How many of the people reading this would be willing to commit to living
> indefinitely on an atoll even if they knew the carbonate production of the
> surrounding water was theoretically adequate to “grow” the islands at a
> rate equal to or greater than SLR?
>
>
>
> Robert W (Bob) Buddemeier
>
> On Tue, Dec 26, 2023 at 1:04 PM Douglas Fenner via Coral-List <
> coral-list at coral.aoml.noaa.gov> wrote:
>
> > Rethinking atoll futures: local resilience to global challenges
> >
> > https://www.cell.com/action/showPdf?pii=S0169-5347%2823%2900298-7
> >
> > open-access
> >
> > Cheers, Doug
> >
> > --
> > Douglas Fenner
> > Lynker Technologies, LLC, Contractor
> > NOAA Fisheries Service
> > Pacific Islands Regional Office
> > Honolulu
> > and:
> > Coral Reef Consulting
> > PO Box 997390
> > Pago Pago, American Samoa 96799-6298  USA
> >
> > Fossil fuel air pollution kills 5 million people world-wide per year
> >
> >
> https://www.yahoo.com/news/research-shows-disturbing-between-millions-200000257.html
> >
> > World's richest 1% emit as much as 5 billion people
> > https://makerichpolluterspay.org/climate-equality-report/
> >
> > Huge expansion of fossil fuels planned, will be very destructive
> >
> >
> https://www.theguardian.com/environment/2023/nov/08/insanity-petrostates-planning-huge-expansion-of-fossil-fuels-says-un-report
> >
> > "without policy changes, the world will heat up enough by the end of the
> > century that more than 2 billion people will live in life-threatening hot
> > climates"         Will you be in that area???
> >
> >
> https://www.yahoo.com/news/scientists-sounding-alarm-dangerous-problem-123000792.html
> >
> > World subsidies for fossil fuels reached an all-time high of over $1
> > TRILLION in 2022, the last year for which data is available.  The
> subsidies
> > MUST end.
> >
> >
> >
> https://blogs.scientificamerican.com/observations/fossil-fuel-subsidies-must-end/
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> >
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