[Coral-List] Atoll good news
dennis.hubbard at oberlin.edu
Tue Jun 16 10:07:46 EDT 2015
These are difficult papers to put into context. All that "p-fish poop" is
also removing carbonate from the reef, so if the production values are
going down, the reef has to lag behind. At that point, wave action is going
to disproportionately remove intertidal sediment from the platform. The
reef is both the basement for island building and the source of the
sediment. Increased grazing might seem to just increase island supply, but
the problem is that the carbonate budget is only as healthy as what is "put
into the bank". Whether or not fish grind more of to to make it available
to the island is less important than the volume of carbonate available. So,
if less carbonate is being made, more of it is being ground away and a
higher percentage is being exported, the end result is a problem for the
The one potential issue with the second paper (I'd need to read it
carefully, so take this as the off the cuff response that it is) is that
these studies are often based on plan (i.e. map, air photo) measurements
and therefore report results in square meters. Perhaps the second paper
took elevation into account, but many that I've seen recently have not -
stay tuned. In this methodology, an eroded area 5 meters high is treated as
equal to a depositional area only a meter or so ihigh. As a result, the
area stays the same, but volume is being lost. Also, most of the studies
that have also characterized the positions of the islands on the atolls
show island masses gradually moving toward the center of the atoll. As the
islands encounter to slope down into the lagoon, the island will
increasingly have difficulty - the same as if the seds were doing down the
front. And.... many excellent papers have shown that the increasing
inundation due to greater storm surge will leave many (not all) islands
uninhabitable long before they are underwater.
As with corals where we confuse calcification, linear extension, density
and "growth rate", the issue with islands is how we define "drowning".
Waiting for the highest point on the tallest dune is much different than
the point where the island has been rendered uninhabitable. There is an
interesting wrinkle in the Law of the Sea. Once an island becomes "an
uninhabitable rock" it legally ceases to be sovereign territory and the
former inhabitant's claims (or their government on a nearby island) to
offshore sovereignty likewise disappears. This will mean that there are
going to be a bunch of mining companies waiting in line to treat nearshore
shelves as international waters. There is no practical usefulness for
science without a reason for doing it, but there is no good management
without both good science and a full understanding of the vagaries of
policy and politics. That's a discussion for another day.
On Mon, Jun 15, 2015 at 3:18 PM, Eugene Shinn <eugeneshinn at mail.usf.edu>
> I would like to alert readers of two interesting peer reviewed article
> in the current issue of GEOLOGY.
> The first article on page 503 listed below demonstrates that Vakkaru
> Island, an atoll carbonate sand island in the Maldives is mainly
> composed of Parrotfish poop. Authors catalogued sand components and
> accessed amount of carbonate sand Parrot fish generate by munching
> surrounding reef at 5.7 kg / m^2 each year. Storms transport this sand
> onto the island in the center of the atoll.Parrotfish are mainly
> responsible for the islands existence. One can only speculate that the
> dozens of other similar islands in the Maldives chain have similar origins.
> The Second article on page 515 concludes that Funafuti atoll in the
> central Pacific has experienced some of the highest rates of sea level
> rise over the past 60 years (5.1 plus or minus 0.7mm/year). No evidence
> of heightened erosion of islands over the past half century while sea
> level rise has accelerated and none of the islands have disappeared.
> That’s good news for the islands residents. Gene
> 1.C.T. Perry et al., 2015, Linking reef ecology to island building:
> Parrotfish identified as major producers of island-building sediment in
> the Maldives. Geology v. 43 no 6. P. 503-506.
> 2.P. S. Kench et al. 2015, Coral islands defy sea-level rise over the
> past century: Records from a central Pacific atoll. Geology v. 43, no.6.
> p. 515-518.
> No Rocks, No Water, No Ecosystem (EAS)
> ------------------------------------ -----------------------------------
> E. A. Shinn, Courtesy Professor
> University of South Florida
> College of Marine Science Room 221A
> 140 Seventh Avenue South
> St. Petersburg, FL 33701
> <eugeneshinn at mail.usf.edu>
> Tel 727 553-1158
> ---------------------------------- -----------------------------------
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Chair, Dept of Geology-Oberlin College Oberlin OH 44074
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