Seychelles: Ecott report of coral bleaching

[Dr John R Turner]

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