424
N. BALAKRISHNAN NAIR AND M. SARASWATHY
near the bottom (Greenfield, 1952). I n a station where there was uniform salinity at all depths, the species occurred in great numbers at the
surface. I n another locality at the mouth of the Miami river where
there was uniform attack by borers throughout the vertical column, the
salinity was found to be higher than up river with the surface layer
showing evidence of dilution with fresh water (Greenfield, 1952). The
vertical distribution of shipworms may also be influenced by other
factors. Isham et al. (1951) noticed maximum attack at 166 ft candles
decreasing at both higher and lower light intensities. Owen (1953a)
observed greater attack by Teredo norvegica with increase in depth and
in dimly lit regions of Loch Ryan. According t o Rancurel (1951) larvae
of T . pedicellata are photopositive up to metamorphosis and Greenfield
(1952) has suggested the effect of a negative geotactic response.
More reliable information on vertical distribution can be obtained by
selecting suitable test sites at several places in an estuary and by following the effects of salt water intrusion and other factors. Data
obtained from piles and poles removed from a harbour area after being
in water for several years may not give a reliable picture of the sequence
of events that take place in regard to larval settlement. They reveal
only the total attack by a variety of borers under the influence of the
prevailing physical, chemical and biological factors during the period
the pile was in water. Examination of the pattern of distribution based
on panels exposed for long periods of time and involving more than one
species of borer is also likely t o present only a general picture. Detailed
observations with a methodically operated system of panels side by
side with examination of hydrographical data alone can ensure reliable
conclusions about the pattern of distribution. Differences in the magnitude of the strike is probable in the same locality even in successive
years but the nature of relationship of the different species t o the combination of environmental factors may be almost the same.
XII. TEREDINIDS IN DEEP WATER
Shipworms are not confined to shallow coastal waters where,
through the agency of man, they have access t o a greater amount of
substrata than elsewhere in the sea. Shipworms do also occur in deep
water. Bartsch (1927) has collected and described several species from
dredged pieces of timber obtained by the Albatross Philippine Expedition in depths ranging from 51-548 m. Roch (1940) records Teredo
utriculus ( =Nototeredo norvagica according t o Turner) recovered from
the jute layer of a cable removed from a depth of 700 m. Turner (1966)
reports the occurrence of Bankia carinata (Gray) at 7 488 m in the Banda
Sea, Uperotus clavus (Gmelin) from pandanus fruit at the same station,
N. BALAKRISHNAN NAIR AND M. SARASWATHY
near the bottom (Greenfield, 1952). I n a station where there was uniform salinity at all depths, the species occurred in great numbers at the
surface. I n another locality at the mouth of the Miami river where
there was uniform attack by borers throughout the vertical column, the
salinity was found to be higher than up river with the surface layer
showing evidence of dilution with fresh water (Greenfield, 1952). The
vertical distribution of shipworms may also be influenced by other
factors. Isham et al. (1951) noticed maximum attack at 166 ft candles
decreasing at both higher and lower light intensities. Owen (1953a)
observed greater attack by Teredo norvegica with increase in depth and
in dimly lit regions of Loch Ryan. According t o Rancurel (1951) larvae
of T . pedicellata are photopositive up to metamorphosis and Greenfield
(1952) has suggested the effect of a negative geotactic response.
More reliable information on vertical distribution can be obtained by
selecting suitable test sites at several places in an estuary and by following the effects of salt water intrusion and other factors. Data
obtained from piles and poles removed from a harbour area after being
in water for several years may not give a reliable picture of the sequence
of events that take place in regard to larval settlement. They reveal
only the total attack by a variety of borers under the influence of the
prevailing physical, chemical and biological factors during the period
the pile was in water. Examination of the pattern of distribution based
on panels exposed for long periods of time and involving more than one
species of borer is also likely t o present only a general picture. Detailed
observations with a methodically operated system of panels side by
side with examination of hydrographical data alone can ensure reliable
conclusions about the pattern of distribution. Differences in the magnitude of the strike is probable in the same locality even in successive
years but the nature of relationship of the different species t o the combination of environmental factors may be almost the same.
XII. TEREDINIDS IN DEEP WATER
Shipworms are not confined to shallow coastal waters where,
through the agency of man, they have access t o a greater amount of
substrata than elsewhere in the sea. Shipworms do also occur in deep
water. Bartsch (1927) has collected and described several species from
dredged pieces of timber obtained by the Albatross Philippine Expedition in depths ranging from 51-548 m. Roch (1940) records Teredo
utriculus ( =Nototeredo norvagica according t o Turner) recovered from
the jute layer of a cable removed from a depth of 700 m. Turner (1966)
reports the occurrence of Bankia carinata (Gray) at 7 488 m in the Banda
Sea, Uperotus clavus (Gmelin) from pandanus fruit at the same station,