What are the short - term effect from coral bleaching?

Coral bleaching is caused by the healthy coral reef losing its tiny, single-sell algea and usually occurs quite suddenly. coral bleaching is known to be responsible for 18% of the worlds coral reefs, in most cases its triggered by the introduction of warmer waters than normal 

Widespread, intense coral bleaching and mortality occurred across the Ryukyu Islands, southern Japan, in the summer and autumn of 1998. All of the corals within the study area, dominated by arborescent Acropora, at Iriomote Island (Ryukyu Islands), had been bleached by October 1998, and were completely dead and covered by filamentous algae in October 1999. The adult fish assemblage in the area was monitored before (1995-1997), during (1998), and after (1999) the bleaching event, the monitored area during those intervals being termed ‘living’, ‘bleaching’, and ‘dead’ coral areas, respectively. The numbers of fish species and individuals were significantly greater in the living and bleaching coral areas than in the dead coral area, there being no differences in these variables between the former two areas. The reduction in numbers in the dead coral area was due to the complete disappearance of obligate corallivores. These results suggest that fishes other than corallivores have no particular response to coral bleaching and subsequent mortality as long as the high structural complexity of bleached corals is preserved.

The correct answer would be b

From a high concentration to a low concentration.