240
C. M. YONOE
genera containing zooxanthellae are reduced. The degree of reduction
appears to be directly correlated with the abundance of zooxanthellae
in the series Lobophytum-Sarcophytum-Alcyonium (tropical species)Sclerophyturn leading up to the Xeniidae in which these filaments are
so reduced as to appear functionless. All of these genera demand Iight.
Other tropical genera, such as Acabaria and other species of Clawularicr
(Gohar, i940), apparently live as well in dim as in bright light.
As noted elsewhere (Yonge, 1957), the process of establishing an
association between an animal and a unicellular plant must differ
according to whether the animals be carnivorous (as in the Sclemctinia)
or herbivorous as these Alcyonacea appear to have become. I n the
former the animal must be initially specialized to take in and tolerate
the plants, in the latter it is the plant which must be specialized to resist
digestion within the animal. Certainly the end result in the two c a m is
very different although some source of energy additional to the zooxanthellae would appear neoessary in the Xeniidae. The retention of the
mouth, although narrow, is possibly significant.
Alcyonacen are often extremely abundant on Indo-Pacific (not
West Indian) reefs. Thus on Low Isles they are a dominant part of the
fauna, many of the colonies being large and in combined bulk covering
wide areas especially in the sheltered anchorage zone as noted at the
time of the Expedition and more recently by Stephenson et al. (1958)
who noted their presence from M.L.W. to at least 20 f t below L.W.S.
Sarwphyton trocheliophorum, Lobophytum cramum and L. pawifirum
valdum were conspicuous, Simularia variabilis, S. jlexibilis, 8. polydactyla and Sphaerella echinata were very common and Sinularis
conferta gracilis and Sphaerella echinuta were also present. Elsewhere
Nephthea mollis is common, while speciea of Xenia, Heteroxenh,
Cespitularia, Cluvuluria, Pach ycEavularia and Alcyonium also ocuur.
There seems little information about the abundance of these ‘‘soft
corals ” on the Pacific atolls.
A thorough and comparative study of feeding and digestion, in
Alcyonacea showing all conditions from lack of zooxanthellae to their
presence in greatest abundance, as in the Xeniidae, wouId be of the
greatest value both for its own sake and for the light the results might
show on conditions in the hermatypic corals.
(2) There have been many and extensive estimates of the oxygen
produced by the zooxanthellae in the course of photosynthesis notably
during the Great Barrier Reef Expedition (Yonge et al., 1932). It wa8
also found that respiration is unaffected by oxygen tension until this
drops to between 40 and 50% saturation. mere is certainly no recent
evidence to support the view that the oxygen produced by the zooxan-
C. M. YONOE
genera containing zooxanthellae are reduced. The degree of reduction
appears to be directly correlated with the abundance of zooxanthellae
in the series Lobophytum-Sarcophytum-Alcyonium (tropical species)Sclerophyturn leading up to the Xeniidae in which these filaments are
so reduced as to appear functionless. All of these genera demand Iight.
Other tropical genera, such as Acabaria and other species of Clawularicr
(Gohar, i940), apparently live as well in dim as in bright light.
As noted elsewhere (Yonge, 1957), the process of establishing an
association between an animal and a unicellular plant must differ
according to whether the animals be carnivorous (as in the Sclemctinia)
or herbivorous as these Alcyonacea appear to have become. I n the
former the animal must be initially specialized to take in and tolerate
the plants, in the latter it is the plant which must be specialized to resist
digestion within the animal. Certainly the end result in the two c a m is
very different although some source of energy additional to the zooxanthellae would appear neoessary in the Xeniidae. The retention of the
mouth, although narrow, is possibly significant.
Alcyonacen are often extremely abundant on Indo-Pacific (not
West Indian) reefs. Thus on Low Isles they are a dominant part of the
fauna, many of the colonies being large and in combined bulk covering
wide areas especially in the sheltered anchorage zone as noted at the
time of the Expedition and more recently by Stephenson et al. (1958)
who noted their presence from M.L.W. to at least 20 f t below L.W.S.
Sarwphyton trocheliophorum, Lobophytum cramum and L. pawifirum
valdum were conspicuous, Simularia variabilis, S. jlexibilis, 8. polydactyla and Sphaerella echinata were very common and Sinularis
conferta gracilis and Sphaerella echinuta were also present. Elsewhere
Nephthea mollis is common, while speciea of Xenia, Heteroxenh,
Cespitularia, Cluvuluria, Pach ycEavularia and Alcyonium also ocuur.
There seems little information about the abundance of these ‘‘soft
corals ” on the Pacific atolls.
A thorough and comparative study of feeding and digestion, in
Alcyonacea showing all conditions from lack of zooxanthellae to their
presence in greatest abundance, as in the Xeniidae, wouId be of the
greatest value both for its own sake and for the light the results might
show on conditions in the hermatypic corals.
(2) There have been many and extensive estimates of the oxygen
produced by the zooxanthellae in the course of photosynthesis notably
during the Great Barrier Reef Expedition (Yonge et al., 1932). It wa8
also found that respiration is unaffected by oxygen tension until this
drops to between 40 and 50% saturation. mere is certainly no recent
evidence to support the view that the oxygen produced by the zooxan-