Etude de la variabilité spatio-temporelle de densité Etude de la variabilité spatio-temporelle de densité Cas de Grand récif de Toliara et complexe récifale de Sarodranot complexe récifale

Abstract

A study has been led from September 2016 to February 2017 in the great barrier reef of Toliara and
the complex reef of Sarodrano. It concerns about assessing the density of Zooxanthellae in Acropora
sp during the hot season in two different sites. The sample of healthy Acropora sp was collected in
two gradients of depth (0-5m) and (5-10m) every two months. For the first two months, the density of
zooxanthellae in Grande Vasque was respectively about 1,4*106 cells.cm-² and 1,54*106 cells.cm-² in
(0-5m) depth and (5-10m). In Arakaivo, there is no significant difference in terms of density between
the gradient of depths. In November and December we have observed a significant value between
depth either in Grande Vasque or Arakaivo. And a significant difference was noted between the two
sites in terms of density. The zooxanthellae dwells the most in the apical part of coral. There is a
significant difference either between apical and middle or apical and basal part of coral. The
Zooxanthellae set up likely the most on the top of Acropora sp so that it conquered the daily light.
And about the carbon sequestration, the basal part of coral has a higher amount of CO2 than the
middle or apical part of coral. This result is very important to diagnose the state of coral reef
ecosystem before, during and after one event.
Keys words : Acropora sp, Zooxanthellae, Density, CO2, GRT, Sarodrano