16 Reefscape Ecology Within the South Pacific
259
pigments contained in zooxanthellae (coral endosymbionts) in favour of pigments
associated with algal turf and macroalgae. The colour composition reflected by the
coral pigments is typically richer than the composition inherent to algae (Collin and
Planes 2012). Since the second acquisition is from March 2010, namely after the cyclonic event, the geomorphological and spectral evolution extracted from the satellite
images result from the cumulated effect of both disturbances without any chance to
dissociate their respective contribution. However, the in situ panoramic survey shows
a critical simplification of the reef structure at a small scale, as defined in the literature (e.g. Chabanet et al. 2005; Murdoch and Aronson 1999). With a higher temporal
resolution compared to our satellite data, this survey allows speculating about the
relative effect of A. planci and the cyclone. In November 2006, the A. planci outbreak
was already occurring on Moorea island (Clark and Weiztman 2008). The negative
influence of coral predation on the deterioration of the coral cover therefore happened
from 2006 to the cyclonic event of 2010. This result corroborates the conclusions of
Adam et al. (2011) and Trapon et al. (2011). The latter authors also indicate that the
impact resulting from the A. planci proliferation is more detrimental than the effect
of a cyclone. A scene from 2009 would allow confirming that A. planci is mitigating
the coral colour diversity without altering the structural complexity of the colonies.
We can point out upfront that the entropy will show a marked difference from 2006
to 2009 whilst the bathymetric variance will remain unchanged.
16.4.2 Resistance of Coral Fishes and Corals
In addition to the coral cover survey, an assessment of the specific richness of coral
fishes was achieved along Tiahura transect (Lison de Loma pers. comm.). The evolution of the richness between 2005 and 2011 differs from the evolution of the coral
cover (Fig. 16.10). From 2005 to 2009, while the coral cover decreases from 40 to
1 %, the specific richness slightly increases, varying from 41 to 46 fish species. It can
be inferred that the predation of A. planci acts specifically on the coral cover but has
no clear influence on the ichthyologic specific richness. We can reasonably assume
that A. planci feeds on coral colonies but leaves unaffected their structural complexity and the resulting variety of ecological niches constituting as many habitats for the
inherent ichthyologic species. The small increase of the specific richness can also be
supported by the results of Adam et al. (2011) indicating an increasing number of
herbivorous fishes on Moorea outer reef during a decrease of the coral cover subsequent to a severe event of predation by A. planci. This excess of herbivorous species
might be fostered by the novel expansion of algal turf and macroalgae they feed
on so that algae are not able to outcompete coral cover regeneration. From 2009 to
2011, whilst the coral cover remains around 1 %, the ichthyologic species richness
decreases (from 46 to 36 species). These results could be the direct consequence
of the cyclone Oli. Following the smoothing of the outer reef by the cyclonic swell
and the decrease of the complexity of the coral structures as well as the subsequent
ecological niches, the number of fish species tends to decline along with habitat loss.
259
pigments contained in zooxanthellae (coral endosymbionts) in favour of pigments
associated with algal turf and macroalgae. The colour composition reflected by the
coral pigments is typically richer than the composition inherent to algae (Collin and
Planes 2012). Since the second acquisition is from March 2010, namely after the cyclonic event, the geomorphological and spectral evolution extracted from the satellite
images result from the cumulated effect of both disturbances without any chance to
dissociate their respective contribution. However, the in situ panoramic survey shows
a critical simplification of the reef structure at a small scale, as defined in the literature (e.g. Chabanet et al. 2005; Murdoch and Aronson 1999). With a higher temporal
resolution compared to our satellite data, this survey allows speculating about the
relative effect of A. planci and the cyclone. In November 2006, the A. planci outbreak
was already occurring on Moorea island (Clark and Weiztman 2008). The negative
influence of coral predation on the deterioration of the coral cover therefore happened
from 2006 to the cyclonic event of 2010. This result corroborates the conclusions of
Adam et al. (2011) and Trapon et al. (2011). The latter authors also indicate that the
impact resulting from the A. planci proliferation is more detrimental than the effect
of a cyclone. A scene from 2009 would allow confirming that A. planci is mitigating
the coral colour diversity without altering the structural complexity of the colonies.
We can point out upfront that the entropy will show a marked difference from 2006
to 2009 whilst the bathymetric variance will remain unchanged.
16.4.2 Resistance of Coral Fishes and Corals
In addition to the coral cover survey, an assessment of the specific richness of coral
fishes was achieved along Tiahura transect (Lison de Loma pers. comm.). The evolution of the richness between 2005 and 2011 differs from the evolution of the coral
cover (Fig. 16.10). From 2005 to 2009, while the coral cover decreases from 40 to
1 %, the specific richness slightly increases, varying from 41 to 46 fish species. It can
be inferred that the predation of A. planci acts specifically on the coral cover but has
no clear influence on the ichthyologic specific richness. We can reasonably assume
that A. planci feeds on coral colonies but leaves unaffected their structural complexity and the resulting variety of ecological niches constituting as many habitats for the
inherent ichthyologic species. The small increase of the specific richness can also be
supported by the results of Adam et al. (2011) indicating an increasing number of
herbivorous fishes on Moorea outer reef during a decrease of the coral cover subsequent to a severe event of predation by A. planci. This excess of herbivorous species
might be fostered by the novel expansion of algal turf and macroalgae they feed
on so that algae are not able to outcompete coral cover regeneration. From 2009 to
2011, whilst the coral cover remains around 1 %, the ichthyologic species richness
decreases (from 46 to 36 species). These results could be the direct consequence
of the cyclone Oli. Following the smoothing of the outer reef by the cyclonic swell
and the decrease of the complexity of the coral structures as well as the subsequent
ecological niches, the number of fish species tends to decline along with habitat loss.