THE BIOLOGY OF CORAL REEFS
241
thellae is of significant value to the coral, the respimtory needs of which
have been often greatly over-estimated by neglecting the effect of
oxidation of the secreted mucus during the experimental period
(Yonge, 1937).
(3) The presumable increase in metabolic efficiency of hermatypic
corals owing to the presence of zooxanthellae which act as automatic
agents of excretion (as already noted in their utilization of CO, and of
sources of nitrogen and phosphorus) has been particularly stressed by
this author (Yonge, 1940, 1944, 1957). Droop (1963) makes the added
point that tropical animals frequently contain zooxanthellae whereas
their relations in temperate and cold waters do not and associates this
with the higher metabolic rate of the former and so their greater need
for the complementary services of algae. It can be seen how natural
selection would tend to preserve such an aesociation in tropical waters.
It was felt that higher metabolism would involve faster growth
which, although possibly of no particular value to the individual coral
colony might " be an indispensable factor in the necessarily exceptional
powers of skeletal formation possessed by the marine communitiecl
known as ooral reefs '' (Yonge, 1940). Proof of this clearly lay in experiments involving comparisons of growth rates in corals with and without
contained zooxanthellae. It has recently been shown in the important work of Goreau and Goreau (see below) that hermatypic coral8
with zooxanthellae do grow faster than those deprived (by being kept in
the dark) of algae. The major reason for this probably resides in the
direct effect on skeletal formation, i.e. on calcium metabolism. This
leads to consideration of the fourth possible effect of the association,
a t any rate in stony corals, namely as an aid to calcium metabolism.
(4) The possible influence of zooxanthellae on skeleton formation
was experimentally studied by Kawaguti and Sakumoto (1948).
Using four species of corals, they estimated the changes in calcium
content in the relatively small volumes of water in which they had been
kept. They claimed that uptake was greater in the light than in the
dark. However, by using radioactive calcium45 as a tracer, Goreau
( 1969a, 196 1 b) has developed an elegant and precise method enabling him
to measure skeletal growth within a few hours of initial exposure.
Methods have also been devised for the loading and setting out in
natural sites on the reef of weighed and sealed glass jars containing
corals with radioactive calcium-45 in the water, the corals later being
aampled by means of a hollow steel core punch (Goreau and Goreau,
1959). Leaving for later discussion the growth data ao obtained, our
immediate concern is with the process of calcification and the possible
role in this of the zooxanthellae.
241
thellae is of significant value to the coral, the respimtory needs of which
have been often greatly over-estimated by neglecting the effect of
oxidation of the secreted mucus during the experimental period
(Yonge, 1937).
(3) The presumable increase in metabolic efficiency of hermatypic
corals owing to the presence of zooxanthellae which act as automatic
agents of excretion (as already noted in their utilization of CO, and of
sources of nitrogen and phosphorus) has been particularly stressed by
this author (Yonge, 1940, 1944, 1957). Droop (1963) makes the added
point that tropical animals frequently contain zooxanthellae whereas
their relations in temperate and cold waters do not and associates this
with the higher metabolic rate of the former and so their greater need
for the complementary services of algae. It can be seen how natural
selection would tend to preserve such an aesociation in tropical waters.
It was felt that higher metabolism would involve faster growth
which, although possibly of no particular value to the individual coral
colony might " be an indispensable factor in the necessarily exceptional
powers of skeletal formation possessed by the marine communitiecl
known as ooral reefs '' (Yonge, 1940). Proof of this clearly lay in experiments involving comparisons of growth rates in corals with and without
contained zooxanthellae. It has recently been shown in the important work of Goreau and Goreau (see below) that hermatypic coral8
with zooxanthellae do grow faster than those deprived (by being kept in
the dark) of algae. The major reason for this probably resides in the
direct effect on skeletal formation, i.e. on calcium metabolism. This
leads to consideration of the fourth possible effect of the association,
a t any rate in stony corals, namely as an aid to calcium metabolism.
(4) The possible influence of zooxanthellae on skeleton formation
was experimentally studied by Kawaguti and Sakumoto (1948).
Using four species of corals, they estimated the changes in calcium
content in the relatively small volumes of water in which they had been
kept. They claimed that uptake was greater in the light than in the
dark. However, by using radioactive calcium45 as a tracer, Goreau
( 1969a, 196 1 b) has developed an elegant and precise method enabling him
to measure skeletal growth within a few hours of initial exposure.
Methods have also been devised for the loading and setting out in
natural sites on the reef of weighed and sealed glass jars containing
corals with radioactive calcium-45 in the water, the corals later being
aampled by means of a hollow steel core punch (Goreau and Goreau,
1959). Leaving for later discussion the growth data ao obtained, our
immediate concern is with the process of calcification and the possible
role in this of the zooxanthellae.