262
0. M. YONQE
occur in the corals and almost all other coelenterates as well as in
compound ascidians and bivalve Tridacnidae. There are also the bluegreen and filamentous green algae on or in the coral skeletons and
boulders. On the other hand the bulk of the fauna consists of the
sessile animals which harbour these zooxanthellae. Corals are conspicuous but largely because of the great surface exposed. The biomass
is small, there is no succession of overlapping surfaces and colonies
there is off the windward reef margin. All of these animals feed on zooplankton or phytoplankton and almost the only animals capable of
feeding on the calcareous algae are parrot fishes (Smrw) which “ move
about the reef, grazing like a herd of sheep . . . Their tooth marks
remaining on the rocks, are easily observed” (Schultz, 1948). These
predominantly plant communities are not surprisingly autotrophic.
Unable to collect adequate supplies of zooplankton, Sargent and
Austin and also Odum and Odum postulate that corals obtain nutriment
from associated plants. The former indeed state that “ under conditions
of growth on the eastern reef of Rongelap Atoll, the association between
corals and zooxanthellm seems to be essential to the individual colonies
precisely because the corals must derive organic matter from the algae
or die.” They do not explain how this may be achieved. To meet the
same postulated need, Odum and Odum, who estimated that the
zooxanthellae comprised no more than 6% of the total plant mass,
bring in the filamentous boring algae universally present in coral
skeletons. They do not state how the animal codd utilize products from
plants separated from them by an appreciable depth of skelet.al material.
Moreover, Goreau and Goreau (1960b) found that in Municina areolata
the content of filamentous boring algae is very much less than that
estimated by Odum and Odum.
This fundamental problem of coral nutrition has already been
discussed in connexion with Goreau’s work and his conclusion that the
contribution of the zooxanthellae can be no more than some d i h b l e
organic matter which may serve as a vitamin or hormone. Stephens
(1960) has recently shown that Fmgia can remove labelled glucose and
also amino acids from solution. There remains the undoubted, well
demonstrated, fact that corals are most highly adapted for the capture
and extremely rapid digestion of exclusively animal prey and that, in
relation to the bulk of the tissues, they have a literally enormous feeding
surface in most species only exposed at night when zooplankton is
abundant. Nevertheless in view of these contmry views the question
posed by Hand (1956) as to whether corals are herbivorous must,
following further investigation, be conclusively answered.
On the basis of their 6 weeks’ survey of a reef on Eniwetok, Odum and
0. M. YONQE
occur in the corals and almost all other coelenterates as well as in
compound ascidians and bivalve Tridacnidae. There are also the bluegreen and filamentous green algae on or in the coral skeletons and
boulders. On the other hand the bulk of the fauna consists of the
sessile animals which harbour these zooxanthellae. Corals are conspicuous but largely because of the great surface exposed. The biomass
is small, there is no succession of overlapping surfaces and colonies
there is off the windward reef margin. All of these animals feed on zooplankton or phytoplankton and almost the only animals capable of
feeding on the calcareous algae are parrot fishes (Smrw) which “ move
about the reef, grazing like a herd of sheep . . . Their tooth marks
remaining on the rocks, are easily observed” (Schultz, 1948). These
predominantly plant communities are not surprisingly autotrophic.
Unable to collect adequate supplies of zooplankton, Sargent and
Austin and also Odum and Odum postulate that corals obtain nutriment
from associated plants. The former indeed state that “ under conditions
of growth on the eastern reef of Rongelap Atoll, the association between
corals and zooxanthellm seems to be essential to the individual colonies
precisely because the corals must derive organic matter from the algae
or die.” They do not explain how this may be achieved. To meet the
same postulated need, Odum and Odum, who estimated that the
zooxanthellae comprised no more than 6% of the total plant mass,
bring in the filamentous boring algae universally present in coral
skeletons. They do not state how the animal codd utilize products from
plants separated from them by an appreciable depth of skelet.al material.
Moreover, Goreau and Goreau (1960b) found that in Municina areolata
the content of filamentous boring algae is very much less than that
estimated by Odum and Odum.
This fundamental problem of coral nutrition has already been
discussed in connexion with Goreau’s work and his conclusion that the
contribution of the zooxanthellae can be no more than some d i h b l e
organic matter which may serve as a vitamin or hormone. Stephens
(1960) has recently shown that Fmgia can remove labelled glucose and
also amino acids from solution. There remains the undoubted, well
demonstrated, fact that corals are most highly adapted for the capture
and extremely rapid digestion of exclusively animal prey and that, in
relation to the bulk of the tissues, they have a literally enormous feeding
surface in most species only exposed at night when zooplankton is
abundant. Nevertheless in view of these contmry views the question
posed by Hand (1956) as to whether corals are herbivorous must,
following further investigation, be conclusively answered.
On the basis of their 6 weeks’ survey of a reef on Eniwetok, Odum and