236
C. M. YONOE
form zooxanthellae (G-A). Both in culture and also in the field,
spherical bodies, each with a delicate flagellum, may appear and swarm
(H, I). These, Freudenthal thinks, may be isogametes whioh on
fusion may also give rise to zooxanthellae (this less certain sequence is
indicated by the broken arrows C-H-I-A).
While all this work has been done on zooxanthellae from Scyphozos
and Actiniaria, the observations of Kawaguti (1944a) leave little doubt
that the zooxanthellae in the hermatypic corals are either the same
species or one with a similar life history. This assumption is here being
made.
B. Signi$cance of the Aumciation
The advantage to the algal symbiont is clear. As “imprisoned
phytoplankton ” they gain protection. Immediate access to a source of
CO, may be significant where algal concentrations rise to 30000 per
mm3; this could otherwise produce severe local deficiency (Droop,
1963). Even more significant are supplies needed for protein synthesis.
We now know much more than that nitrates and phosphates may be
utilized. McLaughlin and Zahl (1959) have shown that as well as these
inorganic sources, the zooxanthellae of Symbiodinium can utilize urea,
uric acid, guanine, adenine or any of the twelve amino acids m a
source of nitrogen, and also a wide range of phosphoric acids. Much,
however, remains to be done on this subject in the experimental field.
Zooxanthellae have been shown to intercept ad phosphate that would
normally Be excreted by hermatypic corals (and is excreted by the
ahermatypic Dendrophyllia). They will aIso remove all phosphate from
2.5 litres of water in which the corals were kept. When the content waa
raised from the normal figure of 3.41 mg/ms to the altogether abnormal
one of 2036 mg of phosphate almost all of this was removed at the end of
5 days (Yonge and Nicholls, 1931a). The removal of ammonia from the
surrounding water has also been demonstrated by Kawaguti (1963).
On the other hand, lowered metabolism-resulting from starvation,
exposure to sub-lethal temperatures or low oxygen tension-causea
immediate ejection, via the “absorptive” zone just within the
mesenterial filaments, of great numbers of algae. In other words, a
major limiting factor in the concentration of zooxanthellae is the
supply, from the animal in which they live, of suitable (and obviously
widely ranging) sources of nitrogen and phosphorus. How much the
content of zooxanthellae can be increased by external addition of such
substances was not, but clearly could be, determined. This has
bearings on the problem of calcification ( ~ e e later).
C. M. YONOE
form zooxanthellae (G-A). Both in culture and also in the field,
spherical bodies, each with a delicate flagellum, may appear and swarm
(H, I). These, Freudenthal thinks, may be isogametes whioh on
fusion may also give rise to zooxanthellae (this less certain sequence is
indicated by the broken arrows C-H-I-A).
While all this work has been done on zooxanthellae from Scyphozos
and Actiniaria, the observations of Kawaguti (1944a) leave little doubt
that the zooxanthellae in the hermatypic corals are either the same
species or one with a similar life history. This assumption is here being
made.
B. Signi$cance of the Aumciation
The advantage to the algal symbiont is clear. As “imprisoned
phytoplankton ” they gain protection. Immediate access to a source of
CO, may be significant where algal concentrations rise to 30000 per
mm3; this could otherwise produce severe local deficiency (Droop,
1963). Even more significant are supplies needed for protein synthesis.
We now know much more than that nitrates and phosphates may be
utilized. McLaughlin and Zahl (1959) have shown that as well as these
inorganic sources, the zooxanthellae of Symbiodinium can utilize urea,
uric acid, guanine, adenine or any of the twelve amino acids m a
source of nitrogen, and also a wide range of phosphoric acids. Much,
however, remains to be done on this subject in the experimental field.
Zooxanthellae have been shown to intercept ad phosphate that would
normally Be excreted by hermatypic corals (and is excreted by the
ahermatypic Dendrophyllia). They will aIso remove all phosphate from
2.5 litres of water in which the corals were kept. When the content waa
raised from the normal figure of 3.41 mg/ms to the altogether abnormal
one of 2036 mg of phosphate almost all of this was removed at the end of
5 days (Yonge and Nicholls, 1931a). The removal of ammonia from the
surrounding water has also been demonstrated by Kawaguti (1963).
On the other hand, lowered metabolism-resulting from starvation,
exposure to sub-lethal temperatures or low oxygen tension-causea
immediate ejection, via the “absorptive” zone just within the
mesenterial filaments, of great numbers of algae. In other words, a
major limiting factor in the concentration of zooxanthellae is the
supply, from the animal in which they live, of suitable (and obviously
widely ranging) sources of nitrogen and phosphorus. How much the
content of zooxanthellae can be increased by external addition of such
substances was not, but clearly could be, determined. This has
bearings on the problem of calcification ( ~ e e later).