THE BIOLOQY OF CORAL REEFS
253
Odum attempted to draw up a balance sheet of gain and loss. While in
the words of Hedgpeth (1957) “This tour de force will probably
excite comment for some years ”, it was surely somewhat premature.
So little is yet known about food chains within a coral reef community ;
indeed the authors themselves are not too accurate about tho trophic
gtatutl of certain of the animals. Thus in their pyramids of biomass,
apart from their assumption that coral are primary producers, they list
the gastropods Cypraea and Thais and the Ophiuroidea all as herbivores
whereas they are specialized carnivores, on the other hand crabs,
indeed decapod Crustacea generally, are omnivores rather than carnivores. However it could be that the final estimate in dry biomass in
grams per square metro of carnivores 11, herbivores 132, primary
producers 703, may be a reasonable approximation.
But the prime criticism of this admittedly bold and very interesting
attempt lies in tho basic failure to distingukh between the outer seaward growing (or certainly maintaining) margin of the reef and the
upper reef flat with the encircled lagoon. With little doubt the latter
regions are in a more or less steady state with gain from and loss to the
ocean roughly balanced. I n the words of Odum and Odum, under
present ocean levels the reef community may represent ‘ I a true ecological climax or open steady-state system ”. Certainly the lagoon may be
regarded as a localized area within which, over a long period of time
(since late Eocene it would appear in the case of Eniwetok), productivity
has been built up by a gradual accumulation of nutrients needed for
protein synthesis. This has been achieved by intercepting nutrients in
surface waters and, whcrc zooxunthcllao arc present, retaining them in
closed cycle withiri tho ‘ I orgnnim ”. I n (:onRequ(!nco tho lagoor1 arid
mcircling H I I ~ ~ I L W rcvf i N riow i L n iircii of high productivity in ocoanic
watcm o f t\.utrtwwly low productivity. Sorno measure of the difference
niiiy bc- iinplicd in the cstirnato of Emcry et al. (1954) that sedimentation
on the summit of an atoll is about 1000 times faster than in the
mrrounding dcptlis. In the warm, well illuminated and well mixed
lagoon wntcrx thrrc is a rapid turnover of tho cndcmic planktonic and
benthic population, although whother this amounts to an annual
replacement by as much as 12.5 times the average standing crop,
which is what Odum and Odum estimate, remains to be confirmed.
All this takes 110 account of the outer seaward surface. There,
the hermatypic corals and associated animals can only be maintained
from oceanic sources-and if they are not maintained the whole reef
formation will be disrupted. There is no nutritional connexion with
the reef flat and the lagoon. This exposed, seaward community iR
outside the closed system where essential nutrients aro retained and
253
Odum attempted to draw up a balance sheet of gain and loss. While in
the words of Hedgpeth (1957) “This tour de force will probably
excite comment for some years ”, it was surely somewhat premature.
So little is yet known about food chains within a coral reef community ;
indeed the authors themselves are not too accurate about tho trophic
gtatutl of certain of the animals. Thus in their pyramids of biomass,
apart from their assumption that coral are primary producers, they list
the gastropods Cypraea and Thais and the Ophiuroidea all as herbivores
whereas they are specialized carnivores, on the other hand crabs,
indeed decapod Crustacea generally, are omnivores rather than carnivores. However it could be that the final estimate in dry biomass in
grams per square metro of carnivores 11, herbivores 132, primary
producers 703, may be a reasonable approximation.
But the prime criticism of this admittedly bold and very interesting
attempt lies in tho basic failure to distingukh between the outer seaward growing (or certainly maintaining) margin of the reef and the
upper reef flat with the encircled lagoon. With little doubt the latter
regions are in a more or less steady state with gain from and loss to the
ocean roughly balanced. I n the words of Odum and Odum, under
present ocean levels the reef community may represent ‘ I a true ecological climax or open steady-state system ”. Certainly the lagoon may be
regarded as a localized area within which, over a long period of time
(since late Eocene it would appear in the case of Eniwetok), productivity
has been built up by a gradual accumulation of nutrients needed for
protein synthesis. This has been achieved by intercepting nutrients in
surface waters and, whcrc zooxunthcllao arc present, retaining them in
closed cycle withiri tho ‘ I orgnnim ”. I n (:onRequ(!nco tho lagoor1 arid
mcircling H I I ~ ~ I L W rcvf i N riow i L n iircii of high productivity in ocoanic
watcm o f t\.utrtwwly low productivity. Sorno measure of the difference
niiiy bc- iinplicd in the cstirnato of Emcry et al. (1954) that sedimentation
on the summit of an atoll is about 1000 times faster than in the
mrrounding dcptlis. In the warm, well illuminated and well mixed
lagoon wntcrx thrrc is a rapid turnover of tho cndcmic planktonic and
benthic population, although whother this amounts to an annual
replacement by as much as 12.5 times the average standing crop,
which is what Odum and Odum estimate, remains to be confirmed.
All this takes 110 account of the outer seaward surface. There,
the hermatypic corals and associated animals can only be maintained
from oceanic sources-and if they are not maintained the whole reef
formation will be disrupted. There is no nutritional connexion with
the reef flat and the lagoon. This exposed, seaward community iR
outside the closed system where essential nutrients aro retained and