CORDIO Status Report 2002.pdf

Table 9.
Summary of indicator fish data from six sites in Nosy Be region
Nosy Nosy Nosy Nosy Be Nosy Be Nosy Be
Mitsio Sakitia Tanikely North Northwest Lokebe Reef
Number Species
Observed 5 4 5 6 4 4
Large schools N N Y N Y N
observed at all sites, were the red fin butterfly fish,
Chaetodon trifasciatus and the Black spotted emperor,
Lethrinus harak. Chaetodon trifasciatus was found, usually
in pairs associated with coral. Nosy Sakitia and North
Nosy Be supported the highest abundance of this species.
Lethrinus harak was found in high numbers associated
with sandy patches at Nosy Mitsio and Lokobe
Reef (Table 8).
Most other fish indicator species were found rarely or
in low numbers, however, two species were observed in
schools in high numbers, Lutjanus monostigma at North
Nosy Be and Plectorhinchus gaterinus at Nosy Tanikely
(Table 9).
DISCUSSION
Health of Fringing Reefs
The coral reefs examined in this study in 1999 appeared
to be in good condition. The percentage of live coral
cover (27–53%) was slightly lower than reported for
other studies in the Nosy Be region (Wilkinson, 2000).
However, compared to other major islands in the region
(Wilkinson, 2000); areas along the African coast (Mc-
Clanahan & Obura, 1997; McClanahan & Shafir,
1990); and the global average of 33% (Hodgson, 1999),
live coral cover was high.
The percentage of dead coral cover was generally less
than 10%, which suggests the areas examined were not
strongly affected by the 1998 global coral bleaching
event. There was some evidence of low levels of bleaching
at all of the North Nosy Be, North West Nosy Be
and Lokebe Reef. Other studies in different parts of
Madagascar report much higher levels of bleaching
(80–90% in Mclanahan & Obura, 1998; 20–50% in
Wilkinson, 1998). All of the reefs examined were; in
>3m of water, along a reef slope, and exposed to currents
and, therefore, maybe have been less vulnerable to increased
water temperatures. Alternatively, coral bleaching
may have been more extensive earlier and the reefs
have recovered. The low percentage of dead coral is
consistent with the known absence of highly destructive
activities such as dynamite blasting and coral mining.
The number of outbreak species was generally low.
No specimens of Acanthaster planci or Drupella cornis
were observed at any of the sites and, in general, the
densities of Diadema setosum were much lower than reported
for similar unprotected areas in Kenya (Mc-
Clanahan & Shafir, 1990). Whilst not examined directly
it was noted that the density of all sea urchin species was
much lower than reported on heavily fished areas in
Kenya (140 ± 81 per 10 m 2 in McClanahan & Shafir,
1990). These authors have reported a negative association
between numbers of fish and fish species and sea
urchin density. This may indicate reefs examined in the
Nosy Be region were not under severe stress or similar
intense fishing pressure.
Coral diversity in terms of total number of genera
observed at each site (ranging from 18–35) and for all
sites combined (42) was lower than reported for studies
around Nosy Be (63) (IUCN 1988). However, considering
the survey areas were restricted to transects, the
number of coral genera recorded were high. A similar
transect based study in Kenya identified only up to 25
coral genera (McClanahan & Obura, 1997).
The sites with the greatest diversity were Nosy Sakatia
199