Seychelles: Ecott report of coral bleaching

Olof Linden olof at timmermon.se
Wed Sep 20 02:36:03 EDT 2000


John, Tim, Coral-list,
Let me just add that the CORDIO Status Report 2000 is in print and will be
available October 1st.
Olof Linden

----- Original Message -----
From: Dr John R Turner <J.turner at bangor.ac.uk>
To: coral-list admin <jch at coral.aoml.noaa.gov>
Cc: <coral-list at coral.aoml.noaa.gov>; <timecott at hotmail.com>
Sent: Tuesday, September 19, 2000 9:19 PM
Subject: Re: Seychelles: Ecott report of coral bleaching


> Dear Coral list,
>
> The status of coral reefs in the granitic islands of the Seychelles
archipelago
> has recently been assessed by two independent surveys following the mass
> mortality caused by the 1997/98 bleaching event. Engelhardt, working in
> collaboration with the Seychelles Department of Conservation surveyed 15
sites
> located mainly on the north west coast of Mahe during November and
December
> 1999.  During January 2000, Turner, Klaus, Hardman and West, working in
> collaboration with the Seychelles Marine Park Authority, surveyed 46 reef
sites
> mainly to the east of Mahe, including Ste Anne, Ile Moyenne, Ile Cerf,
Cousine,
> Praslin, Curieuse, La Digue, Grand Soeur and Felicite.   Reefs around the
> granitic islands are shallow, and rarely exceed 15m depth.  Both surveys
aimed
> to assess reef structure over the full depth range, with corals identified
to
> genus and species where possible, and assessed reef recovery by recording
new
> colonies believed to have established since the bleaching event.
>
> The combined results of the surveys will shortly be published by CORDIO
(Coral
> Reef Degradation in the Indian Ocean). The abstract of our paper may
answer some
> of Tim Ecotts questions:
> The shallow coral reefs of the Seychelles granitic islands have suffered
severe
> degradation during the two year period following the 1997/98 mass coral
> bleaching event, and signs of recovery are slight.  Live coral cover has
been
> reduced to less than 10% on most reefs around the inner islands, and
partial
> mortality of colonies is high.   Dead standing coral is present on
sheltered
> reefs, while exposed reefs have already been reduced to rubble.
Zoanthids,
> corallimorpharian anemones, and encrusting red and green calcareous algae
have
> colonised shallow reef slopes and lagoons, and soft corals are growing on
deeper
> reef slopes.  Branching and tabular Acropora species and branching
Pocillopora
> species have died on all reefs.  Surviving corals are massives,
particularly
> Porites, Goniopora, Acanthastrea and Diploastrea.  Remnant coral cover is
> highest in areas dominated by low diversity coral communities largely
composed
> of stress tolerant species such as Porites and Goniopora with low
structural
> complexity. These occur in areas of high turbidity in Beau Vallon Bay and
> adjacent to the harbour on Mahe, which may have escaped high solar
radiation
> during the bleaching event, but are most at risk from land based
activities.
> Most coral species have survived somewhere in the granitic islands, and
hence
> overall coral diversity has been partially reduced in the region, although
> diversity on individual reefs has been severely reduced (to a median of 8
genera
> and 10 species).  Recruitment of the branching corals Acropora and
Pocillopora
> onto the reefs is low, with 35% of the sites surveyed showing no
recruitment.
> Recruits 1-10cms in size have been observed on limestone pavement, dead
standing
> coral and rubble.  These small colonies are vulnerable to predation from
fish
> and urchins, and to damage by abrasion or overturning from mobile
unconsolidated
> substrates during storms. Recruitment may not be effective until
substrates
> become consolidated, and may be dependent on the surviving species in the
> region.  The reefs of the inner islands lack well developed algal ridges,
but
> rather have limestone platforms, from which most corals have died. Death
and
> erosion of the reef edge has exposed many lagoons and shores to wave
action, and
> there are indications of beach erosion on some islands such as La Digue.
There
> is an urgent need to monitor recruitment and to protect live coral and
> recovering reefs, especially in those areas affected by activities on
land,
> fishing and anchoring.
>
> Finally, Emily Hardman begins a PhD this month at the University of Wales
Bangor
> and in the Seychelles (with cooperation from the Marine Park Authority) in
which
> she will be examining the recovery of the reefs around the granitic
islands.
>
> Dr John R Turner
>
> School of Ocean Sciences
> University of Wales, Bangor
> Marine Science Laboratories
> Menai Bridge
> Anglesey
> Gwynedd
> LL59 5EY
> UK
>
> Tel/Fax: +44 (0) 1248 382881
> E mail: J.turner at bangor.ac.uk
> Web site: http://www.sos.bangor.ac.uk
>
>



More information about the Coral-list-old mailing list