MASS MORTALITY OF CORALS AND REEF LIVING FEATURES AT CON DAO ARCHIPELAGO (VIETNAM) IN OCTOBER 2005

Abstract

Con Dao archipelago located in the southeastern waters of Vietnam at 8⁰37’ – 8⁰48’ N and  106⁰32’ - 106⁰45’ E is characterised by diverse terrestrial and marine ecosystems. Coral reefs occupy the area around  1000 ha  with more than 320 hard corals species recorded. A catastrophe causing mass mortally of corals and reef  leaving features occurred in October 2005. Almost coral reefs in the northeastern waters of the archipelago was impacted, indicating mortality of corals ranking from 20% to nearly 100%. The mass mortality is more  serious in reef flats in comparison with that in reef slopes. All hard corals of genera Acropora, Leptoria,  Platygyra, Montipora and Porites died in reef flats meanwhile Galaxea is more resilient to the impact.  Almost non-movable benthic invertebrates also died and density of reef fish decreased seriously on  impacted reefs.

The analysis of water samples and the data recorded by the Station of Meteorology and Hydrology at Con  Dao showed the reason of the catastrophe. Water temperature in Con Dao increased with temperature more  than 30⁰C in lots of days during October, especially more than 31⁰C on 11^th and  12^th October. In the same time, salinity also reduced with value less than 25%o in 7 days. Combination impact of these two factors  were considered as the reason for mass mortality in the event. A hypothesis that fresh water from river  mouths of the Mekong river system was dispersed to the archipelago during this period was recommended for further surveys.