THE BIOLOGY OF WOOD-BORING TEREDINID MOLLUSOS
423
FIU. 41. Curves illustrating the hourly fluctuations in the salinity of the Ernakulrtm
channel. (1) surface; (2) two-metre depth. A, data collected on 9 October 1965;
B, data collected on 8 November 1966.
was probably the comparatively higher salinity at the bottom that inhibited greater settlement at that level so producing an opposite result
to that noted in the fist test. Further, the disparity between settlement at the two levels, top and bottom, is not so conspicuous in the
second test. This is probably the result of the comparatively small
difference between salinity values at the top and bottom levels.
Our data suggest that in the shallow waters of Cochin N . hedleyi
shows significant differences in the intensity of settlement at different
levels during the different periods of the year. This suggests that borer
activity though generally considered most abundant near the bottom
need not necessarily be so at all locations. In waters which are predominantly fresh with the exception of a more saline layer at the mudline resulting from tidal action, Teredo pedicellata were more apparent