THE BIOLOGY OF WOOD-BORING TEREDINID MOLLUSCS
417
It will be seen that temperature appears to be the principal condition determining the periods of breeding. Adult animals can fiequently survive under extremes of temperature which are unfavourable
for reproduction. Consequently a species may maintain itself where
conditions are suitable for reproduction during only a small part of
the year
In making generalizations one should not forget that variables
other than temperature may be directly or indirectly influencing events.
For example, especially along the south-west coast of India, rainfall
reflects the passing seasons, causing great reduction of, as well as
fluctuations in, salinity and so creating conditions unsuitable for
breeding and settlement of certain species.
Events leading t o settlement are dependent on the interplay of
a large number of factors including the physiological characteristics of
the species involved, their geographical distribution, local variations
in the character of temperature changes and the seasonal influence of
other and less obvious aspects of the environment.
XI. THE PATTERN OF VERTICAL SETTLEMENT
In the extensive literature on marine wood boring organisms only a
few deal with the vertical distribution. This information is of considerable value since the degree of deterioration at different levels along
a pile is based on the intensity of settlement and growth of boring
animals at these levels. Further, a study of the varied biological
relations which permit a heterogenous group of boring animals to share
a common and limited habitat such as submerged timber will be of
interest ecologically. Hobby (1918) noted on sample piles in the shallow
waters of Manati Bay in eastern Cuba an increase in attack by shipworms from low water level to the mud line. Quicker deterioration at
the mud-line has also been noticed by Johnson (1918) in the same area.
McDougall (1943) noted at Beaufort, N. Carolina that infestation by
Banlcia gouldi was heaviest near the mud line. Edmondson (1944)
found out with the aid of test panels in Oahu, Hawaii that the shipworm attack was more severe on the deepest block at a depth of 74 ft
than those at 50 or 25 ft. The species involved were Teredo milleri Dall,
Bartsch and Rehder, Banlcia hwaiiensis Edmondson and Teredo
trzclliformis Miller. At Miami it was observed that the frequency of
attack by both Teredo and the crustacean Limnoria was on the average
three times greater near the bottom than at the surface. Bankia and
Nartesia were more evenly distributed. However, at two stations where
salinity was highest, the pattern of attack was different being greatest
at the surface (Budocks Technical Digest, 1950). At Loch Ryan in
417
It will be seen that temperature appears to be the principal condition determining the periods of breeding. Adult animals can fiequently survive under extremes of temperature which are unfavourable
for reproduction. Consequently a species may maintain itself where
conditions are suitable for reproduction during only a small part of
the year
In making generalizations one should not forget that variables
other than temperature may be directly or indirectly influencing events.
For example, especially along the south-west coast of India, rainfall
reflects the passing seasons, causing great reduction of, as well as
fluctuations in, salinity and so creating conditions unsuitable for
breeding and settlement of certain species.
Events leading t o settlement are dependent on the interplay of
a large number of factors including the physiological characteristics of
the species involved, their geographical distribution, local variations
in the character of temperature changes and the seasonal influence of
other and less obvious aspects of the environment.
XI. THE PATTERN OF VERTICAL SETTLEMENT
In the extensive literature on marine wood boring organisms only a
few deal with the vertical distribution. This information is of considerable value since the degree of deterioration at different levels along
a pile is based on the intensity of settlement and growth of boring
animals at these levels. Further, a study of the varied biological
relations which permit a heterogenous group of boring animals to share
a common and limited habitat such as submerged timber will be of
interest ecologically. Hobby (1918) noted on sample piles in the shallow
waters of Manati Bay in eastern Cuba an increase in attack by shipworms from low water level to the mud line. Quicker deterioration at
the mud-line has also been noticed by Johnson (1918) in the same area.
McDougall (1943) noted at Beaufort, N. Carolina that infestation by
Banlcia gouldi was heaviest near the mud line. Edmondson (1944)
found out with the aid of test panels in Oahu, Hawaii that the shipworm attack was more severe on the deepest block at a depth of 74 ft
than those at 50 or 25 ft. The species involved were Teredo milleri Dall,
Bartsch and Rehder, Banlcia hwaiiensis Edmondson and Teredo
trzclliformis Miller. At Miami it was observed that the frequency of
attack by both Teredo and the crustacean Limnoria was on the average
three times greater near the bottom than at the surface. Bankia and
Nartesia were more evenly distributed. However, at two stations where
salinity was highest, the pattern of attack was different being greatest
at the surface (Budocks Technical Digest, 1950). At Loch Ryan in