Species richness of Gastropods was higher compared to that of
Bivalves and the values decreased after tsunami, however their
species compositions were similar between pre and post tsunami.
Gastropods were dominated by Potamididae while Bivalves
were dominated by Isognomonidae and Ostreidae. In general,
diversity of Gastropods and Bivalves in the study areas was in
lower category. The abundance of Gastropods increased with
increasing vegetation age, but the age of vegetation did not affect
the abundance of Bivalves, and the community structure
at the present study was unstable.
sites 4 and 5, where the dominance index was higher than 0.6,
indicating the dominance index at both stations were fallen
into higher category. While at sites 1, 2, and 3, the dominance
indices were lower than 0.4 and it was categorized into lower
category. Overall, we found that the low diversity index, the
unevenly distributed individuals within species and the moderate
evenness and dominance showed an unstable community
structure at the study sites post tsunami. Macintosh et al (2002)
explained that high dominance of one species probably indicates
a stressful environment while a higher diversity indicates
a stable condition of ecosystem.
For comparison, the stability of Gastropods and Bivalves community
structures in pre tsunami was in moderate category
(Dewiyanti 2005). Meanwhile, the condition of community
structure generally has been changed become unstable in post
tsunami period.