THE BIOLOGY O F WOOD-BORING TEREDINID MOLLUSCS
459
ecological studies by Kirk (1969 a), Jones (1968 a, b, c, 1969) and
Meyers (1968).
H. The effects of water currents upon the rate of attack of shipworms
The rate of water flowing over them is of considerable significance in
the distribution of sessile marine invertebrates. Rock-dwelling species
may be favoured by the scouring action of strong tidal current which
prevents the accumulation of sediment. I n addition to this, the tidal
currents carry oxygen as well as food. Gutsell (1930) observed that
growth of scallops was most rapid in those positions of the Bogue Sound
near Beaufort exposed t o swift tidal currents. Prytherch (1929) found
that larvae of Ostrea virginica settled in greatest numbers on the leeward side of submerged objects where the current was least. Hopkins
(1937) on the other hand noticed that larvae of the Olympia oyster
settled more abundantly on exposure plates that were set parallel with
the current than upon those set perpendicular to it. Similar studies,
though of great practical interest, have rarely been made on marine
borers. Edmondson (1949) found that in Hawaii borers are less prevalent in areas with strong currents than in bays and harbours. Doochin
and Smith (1951) determined the limiting velocity for the attachment of
Teredo pedicellata to be between 1.4 and 1.8 knots whereas the attack
of the isopod, Limnoria, was prevented by currents of between 1.5 and
1.9 knots. The effect of water currents upon the rate of settling of
Teredo furcillatus (= T . furcifera) and Bankia campanellata on timber
has been studied by Nagabhushanam ( 1 9 6 1 ~ )
at the Naval Base in
Visakhapatnam harbour on the east coast of India. He observed that
these borers “require some water current velocity for settling on
timber and that they settle more rapidly when the waters are flowing
than when the waters are still ”. Probably a flow is beneficial in carrying
larger numbm of larvae to the test site.
I. Oxygen content of the water
Teredo navalis collected from test panels exposed at Kristineberg,
Sweden seemed to be little affected by the oxygen content in the water,
the animals remaining active even when this fell t o 0.98 mg/l. In the
medium, oxygen values of 9-59-10-30 mg/l. were measured (Roch,
1932). This species is known to remain tightly closed in its burrow for
long periods with no overt signs of injury (Roch, 1931), when the oxygen
content in the burrow must be greatly reduced. Survival is probably
due to the high glycogen content with efficient mechanisms for anaerobic glycolysis (Lane, 1959a). During such periods investigators (Lane
et al., 1955), noticed decrease in glycogen concentration from 34.0 to
459
ecological studies by Kirk (1969 a), Jones (1968 a, b, c, 1969) and
Meyers (1968).
H. The effects of water currents upon the rate of attack of shipworms
The rate of water flowing over them is of considerable significance in
the distribution of sessile marine invertebrates. Rock-dwelling species
may be favoured by the scouring action of strong tidal current which
prevents the accumulation of sediment. I n addition to this, the tidal
currents carry oxygen as well as food. Gutsell (1930) observed that
growth of scallops was most rapid in those positions of the Bogue Sound
near Beaufort exposed t o swift tidal currents. Prytherch (1929) found
that larvae of Ostrea virginica settled in greatest numbers on the leeward side of submerged objects where the current was least. Hopkins
(1937) on the other hand noticed that larvae of the Olympia oyster
settled more abundantly on exposure plates that were set parallel with
the current than upon those set perpendicular to it. Similar studies,
though of great practical interest, have rarely been made on marine
borers. Edmondson (1949) found that in Hawaii borers are less prevalent in areas with strong currents than in bays and harbours. Doochin
and Smith (1951) determined the limiting velocity for the attachment of
Teredo pedicellata to be between 1.4 and 1.8 knots whereas the attack
of the isopod, Limnoria, was prevented by currents of between 1.5 and
1.9 knots. The effect of water currents upon the rate of settling of
Teredo furcillatus (= T . furcifera) and Bankia campanellata on timber
has been studied by Nagabhushanam ( 1 9 6 1 ~ )
at the Naval Base in
Visakhapatnam harbour on the east coast of India. He observed that
these borers “require some water current velocity for settling on
timber and that they settle more rapidly when the waters are flowing
than when the waters are still ”. Probably a flow is beneficial in carrying
larger numbm of larvae to the test site.
I. Oxygen content of the water
Teredo navalis collected from test panels exposed at Kristineberg,
Sweden seemed to be little affected by the oxygen content in the water,
the animals remaining active even when this fell t o 0.98 mg/l. In the
medium, oxygen values of 9-59-10-30 mg/l. were measured (Roch,
1932). This species is known to remain tightly closed in its burrow for
long periods with no overt signs of injury (Roch, 1931), when the oxygen
content in the burrow must be greatly reduced. Survival is probably
due to the high glycogen content with efficient mechanisms for anaerobic glycolysis (Lane, 1959a). During such periods investigators (Lane
et al., 1955), noticed decrease in glycogen concentration from 34.0 to