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

John McManus jmcmanus at rsmas.miami.edu
Fri Dec 17 11:35:53 EST 2004

Hi Lisa,

An important point about I-P corals is that if the coral patches have not
previously been subjected to periodic siltation, then the corals growing
there will probably not be able to tolerate any substantial amount of silt
(enough to stay on the corals for more than a day). Large Porites heads tend
to try to evict the silt with mucous, and if the currents are not strong
enough, the mucous-silt mess will kill underlying polyps. Other corals
suffer various forms of damage. 

If the coral community is in a chronically very silty area, it will often
likely be predominantly Goniopora, a coral with long polyps that can evict
the silt. Branching corals (Acropora) tend to be sparsely branched and
stretched out, so that sediment does not accumulate on branches. Several
other corals are silt tolerant, but all seem to have ways to remove the silt
and few of those are found abundantly (at least in the same growth forms) on
non-silty reefs. Basically, if you see sediment on any coral that lasts more
than a day, there is cause for concern. And, of course, lower levels of
sediment can reduce light, which isn't a healthy thing to do either.  

Sorry that I cannot give you water turbidity levels, which won't mean much
unless one understands the current patterns and velocities, wave action,
etc. My approach would have more to do with monitoring the corals. 

Note that silt often includes nutrients -- so watch for seaweed growth and
algal blooms. If the dredging becomes periodic, the resilience of the reef
may be impacted even if the corals are not directly affected. In other
words, the next storm might break corals and new ones may no longer
out-compete seaweed for settling space. Or-- the seaweed may actually grow
over the corals. 

Good luck!

 *** Please note new phone numbers (361 now 421) ***
John W. McManus, PhD.
Professor, Marine Biology and Fisheries
Director, National Center for Caribbean Coral Reef Research (NCORE)
Rosenstiel School of Marine and Atmospheric Science
4600 Rickenbacker Causeway, Miami, FL, 33149
305-421-4814, 305-421-4820,       Fax: 305-421-4910
jmcmanus at rsmas.miami.edu

-----Original Message-----
From: coral-list-bounces at coral.aoml.noaa.gov
[mailto:coral-list-bounces at coral.aoml.noaa.gov] On Behalf Of Lisa Kristine
Sent: Thursday, December 16, 2004 10:19 PM
To: coral-list at coral.aoml.noaa.gov
Subject: [Coral-List] Peace Corps- Micronesia: Impacts of coral
dredgingoperations in Yap State

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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