After the occurrence of the tsunami in 2004, the concentration
of nutrients (silicate-silicon, ammoniumnitrogen
and orthophosphate-phosphorus) in the
study areas increased due to tsunami run-up. Thereafter,
chlorophyll a in the water column gradually
increased due to rapid growth of phytoplankton
(red tide outbreak a few months after the tsunami),
and severe coral bleaching also occurred due to the
increase in seawater temperatures to levels higher
than the critical temperature. These conditions
resulted in a mass mortality of corals in shallow
waters. Three years after the 2004 tsunami, the
coral reefs in deep water areas could grow and recover
rapidly although they faced serious bleaching.
Whereas, coral reefs in the shallower waters were
in a poor condition after serious bleaching in May
2005. Mass mortality of corals in shallow waters
was enhanced by high seawater temperature and
high turbidity due to phytoplankton blooms. Turbidity
is thus considered to be the most important factor
leading to the degradation of corals in near shore
shallow areas. Our results indicated that the future
of corals in the Andaman sea, especially in shallow
coastal zones, is threatened. Although it is difficult
to reduce seawater temperature levels caused
by global warming in this region, it is possible to
reduce phytoplankton density and other suspended
particles in water column by decreasing nutrient
loading and sediment runoff caused by domestic
waste sediment and/or local deforestation. The
coral population could vanish in the near future
if stakeholders do not take action to tackle these
problems.