Abstract:
Selected hydrographic parameters of Koggala lagoon over a period of four months in 2002-
2003 are reported together with the preliminary results on the distribution of a marine
bivalve within lagoon. Such data prior to the December 2004 tsunami may provide back-
ground information for comparison of post-tsunami conditions. Moderate yet significant
variation in most physico-chemical parameters was found among selected sites. Mean
salinity decreased from 34.0 ppt at the mouth to 11.4 ppt at 2150 m into the lagoon
indicating pronounced seawater influx and mixing with freshwater. Monthly inter-site
variation in salinity was statistically significant (p<0.05). The marine bivalve Saccostrea
forskalli (Chemnitz) was the dominant benthic mollusk with numbers (per m2) ranging
from 111.5±9.7 at lagoon mouth to 23.5±2.1 at 2150m inner lagoon. Density distribution
of S. forskalli was significantly correlated (p<0.05) with the overall variation in salinity
(r=0.889). Salinity-dependent colonization success of S. forskalli demonstrates the domi-
nance of marine conditions in Koggala lagoon.
