460
N. BALAKRISHNAN NAIR AND M. SARASWATHY
14.3% in 23 days and a corresponding rise in lactic acid (0.02-0.32%)
and pyruvic acid (0.01-0.025%) levels.
J. Hydrogen-ion concentration
Allen and Carter (1924) found specimens of Bankia gouldi at
Beaufort sensitive to increased acidity (pH 2.3) of the medium and
Mawatari (1950) determined the lethal limits for the Japanese species
to be about pH 2-3.
K. The effects of turbidity
Turbidity is an important factor especially for the inhabitants of
shallow coastal waters and of estuarine regions where turbid conditions
are often created by heavy rains and consequent river discharge, wind
action, dredging operations, boat and ship traffic, etc. I n the tropical
regions during the time of the monsoons highly turbid conditions may
exist for weeks or even months.
Presence of silt affects organisms by providing food (Spooner and
Moore, 1940) and influences the transparency of the water affecting the
rate of organic production.
Denison (1852) recorded that muddiness of the water could destroy
shipworms in timber in the harbour at Hobart, Tasmania and at Halifax
in Nova Scotia. The apparent immunity from borer attack of the base
of the piles of Kidderpore Docks in Calcutta has been attributed to the
silty and muddy bottom (Devenish-Meares, 1904). MacKenzie (1927)
and Nair (1962) have reported that both crustacean and molluscan
borers are much less active where the bottom sediment is being continually churned up by propellers.
L. The effects of pollution
The habitats of shipworms, especially those in estuaries, harbours
and similar situations, are subject to the effects of pollution either
through industrial wastes or by human sewage. The pollutants may
consist of solid matter or soluble chemicals of a toxic nature, the
presence of which can affect the organisms directly or they may influence the water, for instance its oxygen content (Tully, 1949). However, some effluents appear to be beneficial (Specht, 1950; Hart et al.,
1933). Hartley (1840) noted that waters with heavy sewage pollution,
or which were influenced by H,S, were comparatively free from shipworms. Similar observations have been recorded from New York
harbour by Jarvis (1855), Buren (1875) and Hoag (1905); from San
Francisco Bay by Hill (1922) ; and from Marseilles by Henry (1909);
N. BALAKRISHNAN NAIR AND M. SARASWATHY
14.3% in 23 days and a corresponding rise in lactic acid (0.02-0.32%)
and pyruvic acid (0.01-0.025%) levels.
J. Hydrogen-ion concentration
Allen and Carter (1924) found specimens of Bankia gouldi at
Beaufort sensitive to increased acidity (pH 2.3) of the medium and
Mawatari (1950) determined the lethal limits for the Japanese species
to be about pH 2-3.
K. The effects of turbidity
Turbidity is an important factor especially for the inhabitants of
shallow coastal waters and of estuarine regions where turbid conditions
are often created by heavy rains and consequent river discharge, wind
action, dredging operations, boat and ship traffic, etc. I n the tropical
regions during the time of the monsoons highly turbid conditions may
exist for weeks or even months.
Presence of silt affects organisms by providing food (Spooner and
Moore, 1940) and influences the transparency of the water affecting the
rate of organic production.
Denison (1852) recorded that muddiness of the water could destroy
shipworms in timber in the harbour at Hobart, Tasmania and at Halifax
in Nova Scotia. The apparent immunity from borer attack of the base
of the piles of Kidderpore Docks in Calcutta has been attributed to the
silty and muddy bottom (Devenish-Meares, 1904). MacKenzie (1927)
and Nair (1962) have reported that both crustacean and molluscan
borers are much less active where the bottom sediment is being continually churned up by propellers.
L. The effects of pollution
The habitats of shipworms, especially those in estuaries, harbours
and similar situations, are subject to the effects of pollution either
through industrial wastes or by human sewage. The pollutants may
consist of solid matter or soluble chemicals of a toxic nature, the
presence of which can affect the organisms directly or they may influence the water, for instance its oxygen content (Tully, 1949). However, some effluents appear to be beneficial (Specht, 1950; Hart et al.,
1933). Hartley (1840) noted that waters with heavy sewage pollution,
or which were influenced by H,S, were comparatively free from shipworms. Similar observations have been recorded from New York
harbour by Jarvis (1855), Buren (1875) and Hoag (1905); from San
Francisco Bay by Hill (1922) ; and from Marseilles by Henry (1909);