462
N. BALAKRISHNAN NAIR AND M. SARASWATHY
settlement and penetration of borers. Atwood (1935) points out that
sewage in itself has little effect but prolonged high pollution may lead to
oxygen depletion which may inhibit the borers but Wedekind (1950)
does not subscribe to this view.
M. The effects of marine fouling
Lehmann’s (1841) finding at Kyholm in Kattegat that wood covered
with colonies of Mytilzcs is apparently immune to attack by ship
worms, the dense mat of byssus threads acting as a mechanical barrier
against the entrance of their larvae, represents one of the early observations on the effect of marine fouling on borer activity. Tests by
Weiss (1948) Redfield and Hutchins (1952) and Nair (1962) have
shown (Fig. 48) that dense fouling accumulations over underwater surfaces can effectively inhibit the attack of both crustacean and molluscan borers. The effect of undisturbed fouling on settlement has d s ~
been studied by Johnson et al. (1936), Johnson and McNeill (1941),
FIG. 49. A test panel with foulers scraped off to reveal the superficial tunnels of
crustacean borers. (From Nair, 1962.)