Status of Coral Reefs of the World 2000

Status of Coral Reefs of the World: 2000
La Reunion Island
Two different locations were chosen, each with 2 monitoring sites: St Gilles - La Saline with
Toboggan, a healthy site, and Planch’Alizes, a disturbed site; and St Leu – Varangue a
reference site, and Corne Nord, near the canal exit. Toboggan has thriving coral
communities with healthy levels of new coral recruitment and a low level of disturbance.
The outer reef-flat is characterised by alternating spurs and grooves towards the seaward
edge. The reef-flat had living coral cover of 31% in 1998, including 22% branching
(Acropora formosa) and digitate (A. humilis) and 9% other coral forms (foliose, encrusting).
Algae cover (8%) was mainly turf algae in damselfish territories (Stegastes nigricans), and
abiotic cover was 62%, mostly fine and coarse sediments. This apparently low level of
living coral is normal for internal reef flats with many broad channels draining the reef flats.
Live coral cover dropped to 22% in 1999, including 20% A. formosa and A. humilis and
2% other foliose and encrusting corals. Algae cover increased from 8% to 11% and abiotic
cover was unchanged on 65%. The drop in coral cover in 1999 was attributed to extreme
low tides that killed the tops of many colonies, which were then invaded by turf algae.
On the outer slope of Toboggan, living coral cover was 57% in 1998, including 26% digitate
(Acropora humilis, A. digitifera) and submassive (A. danae, A. robusta) and 32% other coral
forms, in particular encrusting corals. Algal coverage was 35%, including 31% calcareous algae,
which are typical of wave impacted sites. The area had high coral species diversity like other
turbulent outer slopes. In 1999, living coral cover was 38%, including 23% digitate and
submassive Acropora and 15% other coral forms. Algae cover was 51%, including 39%
calcareous algae. The drop from 57% to 38% was due to coral bleaching, particularly of
Pocillopora, which started in April 98, but was much less than in other Indian Ocean countries.
The Planch’Alizes site is affected markedly by anthropogenic disturbances (coastal waste
discharges, physical destruction, nutrient rich underground water discharges). Coral cover
on the reef flat in 1998 was 18%, including 17% massive, submassive and foliose colonies.
Algal cover was high (37%), mainly turf algae, soft macroalgae and calcareous algae on
dead coral. Abiotic cover of 41% was mostly coarse sediment. Coral cover rose to 48% in
1999, nearly all massive, submassive and foliose forms. Algae coverage dropped to just
13% and abiotic cover was 32% of the total. The major changes are both seasonal and due
to better protection because the area is now clearly marked. The outer slope at 12–13m depth
amongst distinct spur and groove formations had living coral cover around 50%, with 20%
algal cover in 1991, and in 1998, coral cover was 38%, including 24% digitate and submassive
Acropora, 13% others, mainly encrusting forms, 7% soft corals, and 37% algae. In 1999, living
coral cover was 42%, including 27% digitate and submassive Acropora and 15% other coral
forms, in particular encrusting forms. Algae coverage was 39%, including 23% soft macroalgae
and 16% calcareous algae. The variation between the 2 years reflects minor variations in
communities and variations from sampling; the reef showed no real changes over this time.
The Varangue reference site is in the middle of St Leu Ville reef and has been a scientific
study area for several years. Live coral cover on the reef flat was 51%, including 44%
Acropora and 7.4% other foliose, massive and submassive corals in 1999. Algal cover was
18% mostly turf algae, and 31% abiotic cover. This relatively high cover indicates that this
flat is free of excessive sediments and is well irrigated. On the outer slope, living coral
cover was fairly high (53%) and included 23% Acropora and 30% other coral forms (mostly
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