[Coral-List] Peace Corps- Micronesia: Impacts of coral dredging operations in Yap State

Iain Macdonald dr_iamacdonald at yahoo.co.uk
Sun Dec 19 01:26:26 EST 2004

Dear Lisa and List,
The figure given in Rogers (1990) can, sometimes, be viewed as a limit for coral reef growth. For your area, however, the limits for coral survival can be hundreds of mg and not tens. Hodgson has done a lot of work on sedimentation in SE Asia. A lot of work by Stafford-Smith and Ormond document sedimentation tolerance of GBR coral species. But more pertinent to your work from what i have read may be this paper. It is simple but very good. It is a similar situation but in the GBR. It apparently worked very well to curtail turbidity. 


The best thing is that GHD allow you to download for free from their web site see below. I have no connection to this company. I wonder if Dr. Riku might like to comment and inform us of any developments / progress in new papers regarding this topic.


The operation should have at least siltation curtains to minimise impact. Some dredging-coral impacts have shown no long term impact. see siltation refs on the NOAA web page. I am afraid i can not send you any copies as i am 3000 miles from my reference collection.
All the best and keep me informed of anything interesting / progress
Thanks and best regards,
Iain Macd.
PO Box 17458

Lisa Kristine Johnson <johnsolk at gmail.com> wrote:
Dear Coral List serv recipients,

I am a new Peace Corps Volunteer in Yap State, FSM working with the
EPA. My new colleagues have asked for assistance in assessing the
long term effects of dredging operations around the island. I am just
getting started with this project, and am faced with obstacles such as
limited academic resources on island and, unfortunately, my background
not being in this field (during my masters I was focused on crustacean
muscle biochemistry/physiology).

There have been about 10 dredging operations since the 1960s in Yap,
with one currently underway- about 3 months left, according to the
operations manager. The dredging operations are for the purpose of
attaining material to pave roads around the island. Permits, granted
by the EPA Board, are contingent upon daily monitoring of turbidity by
the Public Works engineering office and weekly submissions of these
readings to the EPA. (However, daily monitoring of turbidity nor
weekly submissions occur as the permits require...) The EPA Board has
not yet set turbidity limits, although they are open to

I have read that turbidity around living corals should be no greater
than 10 mg/cm2/d. Dr. Chris Perry's Feb. 2004 list serv comment
regarding siltation and turbidity around corals acknowledged Rogers,
1990 (Marine Ecology Progress Series 62: 185-202) as as good review on
the topic but warned that this is a complicated issue, and that
Indo-Pacific corals are adapted to varying levels of sedimentation
stress. Would anyone be willing to assert an opinion regarding
acceptable turbidity limits some distance away from the "mixing zone"?

The long term effects of dredging on this small, marine
resource-dependent island is of grave concern, and I am really
committed to this issue and helping the EPA Board make educated
decisions about granting/or not granting permits in the future- or
possibly not allowing dredging at all, although ideas concerning an
alternative means of acquiring road paving materials would need to be

This study will be conducted by comparing sites- the dredging site
currently in progress, to sites that have been completed, to sites
that have not been dredged, but are potential sites to be approved by
the Board. Information to include would be water quality
measurements, coral surveys (with the help of a crew of people from
the EPA office and the Yap Marine Resources Management Division),
underwater photo and video footage of sites, and interviews with local

Does anyone have any advice about this subject/project? sources to
suggest? I am currently using John Clark's Coastal Zone Management
Handbook (1996, CRC press) as a guide, but I know that there must be
information out there on this topic, and I would like some advice.

Thank you! Kammagar!
Lisa K. Johnson
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