446
N. BALAKRISHNAN NAIR AND M. SARASWATHY
Recent biochemical studies (Liu and Townsley, 1968) on the digestive
metabolism of cellulose and its derivatives in the caecum of Bankia
setacea have demonstrated the presence of Embden-Meyerhoff pathway,
the pentose cycle, and the citric acid cycle as well as the non-trioare
pathway. Not less than twenty-five enzymes including several Key
enzymes have been identified in the above mentioned pathway. These
authors could not notice the presence of any cellulolytic bacteria in the
caecum of the shipworm. Liu and Walden (1969) have also developed a
quantitative spectrophotometric assay for cellobiase.
XVII. ECOLOGY
There are several environmental factors which affect the natural
populations of shipworms. These are the physico-chemical variables of
sea water, such as temperature, salinity, oxygen tension, turbidity and
pollutants ; the presence and intensity of fouling organisms ; the nature
of the wood, depending on the species of timber, its softness and
orientation of the grain ; the length of exposure of the wood sample in
water ; the presence or absence or the nature of the preservatives used
on it ; the location of the wood in relation to tidal changes, whether or
not it is periodically exposed to desiccation; the orientation of the
sample in relation to depth ; nature of the bottom ; mechanical effects
of currents, their velocity ; conditions of illumination ; the interaction
of the species of wood-boring animals present in the area ; the availability of a suitable substrate during settlement ; the effectiveness of
local larval sources in the case of shipworms and the presence or absence
of predators and parasites. The occurrence, abundance, and so the
intensity of attack, in any locality is dependent on these factors which
vary widely from year to year. Probably there are several more, but
these factors are the most important. Variations in the borer populations from year to year in any locality are no doubt due to a very involved association of these factors, some of which occasionally stand
out as the most responsible ones while other factors, none attaining
conspicuous importance by itself, may collectively exert as much or
more influence than more prominent and easily followed factors. It is
by a constant shifting of importance of these factors and new alignments in their association owing t o ever varying conditions, that accounts for variations in local abundance of shipworms. This would
explain periodically recurring devastations separated by often lengthy
intervals of comparative freedom from attack (Vrolik et al., 1860;
Harting, 1862; Dons, 1949; Scheltema and Truitt, 1954). Reasons for
increased attacks have not all been investigated but they may be
different in different localities such as lowered salinity (Sellius, 1733)
N. BALAKRISHNAN NAIR AND M. SARASWATHY
Recent biochemical studies (Liu and Townsley, 1968) on the digestive
metabolism of cellulose and its derivatives in the caecum of Bankia
setacea have demonstrated the presence of Embden-Meyerhoff pathway,
the pentose cycle, and the citric acid cycle as well as the non-trioare
pathway. Not less than twenty-five enzymes including several Key
enzymes have been identified in the above mentioned pathway. These
authors could not notice the presence of any cellulolytic bacteria in the
caecum of the shipworm. Liu and Walden (1969) have also developed a
quantitative spectrophotometric assay for cellobiase.
XVII. ECOLOGY
There are several environmental factors which affect the natural
populations of shipworms. These are the physico-chemical variables of
sea water, such as temperature, salinity, oxygen tension, turbidity and
pollutants ; the presence and intensity of fouling organisms ; the nature
of the wood, depending on the species of timber, its softness and
orientation of the grain ; the length of exposure of the wood sample in
water ; the presence or absence or the nature of the preservatives used
on it ; the location of the wood in relation to tidal changes, whether or
not it is periodically exposed to desiccation; the orientation of the
sample in relation to depth ; nature of the bottom ; mechanical effects
of currents, their velocity ; conditions of illumination ; the interaction
of the species of wood-boring animals present in the area ; the availability of a suitable substrate during settlement ; the effectiveness of
local larval sources in the case of shipworms and the presence or absence
of predators and parasites. The occurrence, abundance, and so the
intensity of attack, in any locality is dependent on these factors which
vary widely from year to year. Probably there are several more, but
these factors are the most important. Variations in the borer populations from year to year in any locality are no doubt due to a very involved association of these factors, some of which occasionally stand
out as the most responsible ones while other factors, none attaining
conspicuous importance by itself, may collectively exert as much or
more influence than more prominent and easily followed factors. It is
by a constant shifting of importance of these factors and new alignments in their association owing t o ever varying conditions, that accounts for variations in local abundance of shipworms. This would
explain periodically recurring devastations separated by often lengthy
intervals of comparative freedom from attack (Vrolik et al., 1860;
Harting, 1862; Dons, 1949; Scheltema and Truitt, 1954). Reasons for
increased attacks have not all been investigated but they may be
different in different localities such as lowered salinity (Sellius, 1733)