THE BIOLOGY OF CORAL REEFS
245
the greater calcification in darkness when zooxanthellae are present.
The ‘ I voracity ” with which zooxanthellae will take in phosphorus
(and presumably nitrogen) not merely from within the coral but also
from the surrounding medium has already been mentioned (p. 241). It
could be illuminating to discover to what extent the content of zooxanthellac in hennntypic corals could be actually increased by enriching
the external medium with phosphates and ammonia. There is the final
point that if, as suggested by Yonge and Nicholls (1931a), corals do
obtain much of their energy by deominization of protein, the beneficial
effects of the zooxanthellae in removing the end products will be all the
greater.
Thcrc is firially the fact, already noted on p. 218, that the presence
of zooxanthellac appears to bc essential for normal development in
hermatypic corals. This in itself indicates a very intimate metabolic
association between animal and plant.
X. GROWTH
A clear distinction must be made between growth of the tissues and
that of the skeleton even though this is due to the secretory activities
of the tissues. While both obviously increase in young corals there is a
later slowing down in tissue increascs which inevitably affects calcification ; but if the tissues were finally to stop growing completely, calcification would presumably stop, otherwise the tissues would become
increasingly attenuated owing to stretching over the ever-enlarging
skeleton.
Early work on growth was cntirely confined to the results of crtlcification, i.e. to measarcmcnts of lcngth, dinmator or weight of coral8
usually kept uiidcr natiiral conditions. ‘llhcm provided figure3 on
which estimates of ttic possible rate of iricreiw of coral reefs hove heon
based. Information also covering tissue increase was later obtained by
observing increase in the number of polyps, initially in developing
colonies in the laboratory, Later Manton (1932) followed tho growth of
individual branches of Pocillopora bulbosa kept in the sea while Motoda
(1940a) compared the number of polyps (or calyces) in the skeletal mass
in varying sized colonies of Qoniastrea aspera. Thc growth of single free
individuals of Fun& actinifmis ha8 been followed by Aho ( 1940)
who demonstrated some relation between growth and environmont
although without analyzing the factors concerned.
It enlerges from these observations that initial rapid growth rate
of a colony, or of n singlo individual in the case of Fungia, is followed by
ib slowing down leading to almost complete cessation. In Qoniastrea,
245
the greater calcification in darkness when zooxanthellae are present.
The ‘ I voracity ” with which zooxanthellae will take in phosphorus
(and presumably nitrogen) not merely from within the coral but also
from the surrounding medium has already been mentioned (p. 241). It
could be illuminating to discover to what extent the content of zooxanthellac in hennntypic corals could be actually increased by enriching
the external medium with phosphates and ammonia. There is the final
point that if, as suggested by Yonge and Nicholls (1931a), corals do
obtain much of their energy by deominization of protein, the beneficial
effects of the zooxanthellae in removing the end products will be all the
greater.
Thcrc is firially the fact, already noted on p. 218, that the presence
of zooxanthellac appears to bc essential for normal development in
hermatypic corals. This in itself indicates a very intimate metabolic
association between animal and plant.
X. GROWTH
A clear distinction must be made between growth of the tissues and
that of the skeleton even though this is due to the secretory activities
of the tissues. While both obviously increase in young corals there is a
later slowing down in tissue increascs which inevitably affects calcification ; but if the tissues were finally to stop growing completely, calcification would presumably stop, otherwise the tissues would become
increasingly attenuated owing to stretching over the ever-enlarging
skeleton.
Early work on growth was cntirely confined to the results of crtlcification, i.e. to measarcmcnts of lcngth, dinmator or weight of coral8
usually kept uiidcr natiiral conditions. ‘llhcm provided figure3 on
which estimates of ttic possible rate of iricreiw of coral reefs hove heon
based. Information also covering tissue increase was later obtained by
observing increase in the number of polyps, initially in developing
colonies in the laboratory, Later Manton (1932) followed tho growth of
individual branches of Pocillopora bulbosa kept in the sea while Motoda
(1940a) compared the number of polyps (or calyces) in the skeletal mass
in varying sized colonies of Qoniastrea aspera. Thc growth of single free
individuals of Fun& actinifmis ha8 been followed by Aho ( 1940)
who demonstrated some relation between growth and environmont
although without analyzing the factors concerned.
It enlerges from these observations that initial rapid growth rate
of a colony, or of n singlo individual in the case of Fungia, is followed by
ib slowing down leading to almost complete cessation. In Qoniastrea,