[Coral-List] Beach erosion burried corals in Lombok gilis.

[Imam Bachtiar]

Dear John and others,
Thanks very much for your attention on my posting. I would give more detail
about your comments on the erosion of the gilis.
1) It was not very clear about factor retaining the sand previously. There
were some mangrove trees growing in few places as the islands covered by
white sandy beaches. In 1980s many of the mangrove were cut down by local
people. In 1990s, the remaining mangrove are suffered from the erosion and
then the roots are taken out. There was never be any predominance seagrass
in the currently erroded beach, but some algal assemblages was growing in
the sandy bootom reef flat. I am not sure whether these would explain
sand-retaining factors.
2) I have not closely examine the sand, but I think the sand is composed of
a mixture of corals, mollusc, and halimeda. The erosion takes place both in
fished and un-fished (snorkelling) area, that fishing may not be a
contributing factor.
I want to give a good recommendation for the government but I am not sure
yet what is the best one.
Sincerelly,
Imam


On Wed, Jun 10, 2009 at 10:55 PM, John.Cubit <John.Cubit at noaa.gov> wrote:

> Dear Imam Bachtiar,
>
> Based on my experience, these are possibilities I would investigate:
> 1.  Was there a factor retaining the sand previously?  For example,
> seagrasses and rhizophytic ("root"-forming) algae will retain and accumulate
> sand, especially on reef flats as you describe.  If something harms these
> plants, the sand will move.  Alternately, you could plant a "lawn" of these
> plants upstream in the wave-driven coastal flow to retain the sand.
> 2.  In close inspection, what is the sand made of?   Is it fragments of
> calcareous algae, such as Halimeda?   If so, has there been an increased
> growth of the calcareous algae?  With increased human population and
> decreased herbivory/competition, the algae may be more abundant now,
> producing an increased supply of fragments (sand).   Increased nutrients
> from  gardens and septic systems maybe increasing the growth.  Fishing of
> parrot fish and other fish that eat algae may increase the algae.  Death of
> soft corals and other species that normally occupy space now used by the
> algae will increase the algae.
> 3.  If there has been a net change in wave direction, simple barriers will
> retain the sand for a while.  In a tourist area I suspect the sand would be
> valuable to build beaches, use in landscaping, etc.  Beware that changing
> sand movement may have undesirable consequences.  For example, blocking sand
> movement may increase erosion of beaches in other locations, and the
> barriers may divert sand to deeper corals.
>
> I hope this helps.
>
> Regards,
>
> John
> ------------------------
>
> Imam Bachtiar wrote:
>
>>  Dear all,
>> I noticed in the last decade, that beach erosion in the three gilis (Gili
>> Trawangan, Gili Air, and Gili Meno), Lombok - Indonesia, burried living
>> corals and soft corals. The three gilis are the most popular tourist
>> islands. Apparently, the coral burials strated from the southern coast and
>> now reached the northen coast. The snorkling area of the Gili Trawangan
>> are
>> now neraly completely covered by white sand. We can hardly see the living
>> corals and soft corals that previously predominant on this area. The
>> remaining corals are medium size to big colonies of massive corals
>> (Porites). The burials have moved from reef flat down to 15-20 meter
>> depth.
>> Wave actions are now very different from the last decade, when no wave is
>> breaking on the beach. This could be caused by coral degradation due to
>> tourist boat anchorage and increasing wind energy.
>> I am wondering whether any reports or publication about this beach erosion
>> causing coral burial in other places? What should we do to solve this
>> problem?
>> Regards,
>> Imam Bachtiar
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>>
>>
>
> --
> John Cubit, Ph.D.
> Regional Resource Coordinator, Southwest Region
> NOAA Assessment and Restoration Division, Suite 4470
> 501 W. Ocean Blvd.
> Long Beach, CA 90802
> John.Cubit at noaa.gov
> tel 562 980-4081; fax 562 980-4084
> Cell phone (for urgent matters and travel contact) 562 810-4949
>
>