Oligospecific Coral Assemblages

The branching coral Madracis mirabilis occasionally forms large thickets. These assemblages can be well over 500m2. The architecture of these branching corals leads to sediment falling out between their branches. Any structure in the path of water flow will slow down the water flow, thus increased the amount of sediment trapped between the branches. Over time, this process starts burring the corals. These in turn keep growing and as long as the growth rate outruns the sedimentation rate the reef continues to grow.

Although dominated by M. mirabilis, P. porites is another common branching species interspersed in these ologi-specific aggregations. The largest and most impressive ones run perpendicular to the shoreline near Mero where individual ridges reach dimensions of up to 1000 m2. The local dive site where these reefs are found is called Maggie's Point. Smaller formations are found throughout the west coast where reef accretion has take place. At Cachacrou (Scott's Head) only a few remnants of large formations of this kind are alive, due to the heavy use of this reef. In 2007 our survey team also identified small patches of up to approx. 25m2 in the southern region of Dominica near Fond Saint Jean.

The 2005 bleaching episode severely affected the abundance of P. porites, which in 2006 had virtually disappeared from many sites. This was also very evident in the M. mirabilis assemblages, previously containing substantial amounts of P. porites.

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