264
C. M. YONOE
circulated. There is much evidence that the most actively growing
corals are those some metres below the surfon the windward side.
They have the major responsibility for maintaining the stability of the
entire atoll against the constant battering of trade wind sem. This
involves constant replacement of eroded or damaged surf-.
With
the zooxanthellae of essential assistance in maintaining a high rate of
calcification, there must also be a constant supply of food in the form of
zooplankton if only to replace the organic matter continually being lost,
carried around the atoll or dropped into profound depths. There. can be
no closed or autotrophic system in this environment. Although this is
the most difficult of all coral reef environments to penetrate, every
endeavour should be made to sample its waters and obtain some
estimate of the amount of zooplankton, largely no doubt some distance
below the surface, which is carried against these seaward reef surfaces.
The position of the partly downward directed ourrents containing this
essential zooplankton is indicated in Fig. 17, A.
We are thus brought logically to the supreme question which ariws
in any consideration of the biology of coral reefs, namely t o what
extent are the powers of growth capable of withstanding the full force
of the sea; in other words, are modern reefs static, advancing or
retreating? It has long been the opinion of the writer (Yonge, 1940)
that seaward reefs do grow outwards against constant forces of wind
and sea which mould their form. This is the opinion of Kuenen (1960),
and also of Crossland (1962) who makes the point that " Permanent
beds of living coral can exist only immediately along an outgrowing
reef where their foundations are being continually extended." Emery
et al. (1954) consider that the windward reeh at Bikini a p p r to be
growing seaward. Newell (1956), on the other hand, considera that the
seaward reefs at Raroia are getting narrower and that the surge o h e l s
are. formed by erosion, i.e. in opposition to the more general view that it
is the intervening algal ridges which are growing outwards.
By placing permanent marks on reef surfaces it should not be
difficult to discover precisely what is happening. But certainly in the
past the associated powers of growth and high calcification rate have
permitted the formation of reefs exposed to the full force of oceanic
seas. Munk and Sargent (1954) estimate that the wave% beating against
the windward reefs a t Bikini dissipate a force of approximately half a
million horsepower which the ridges and surge channels sucoe~ully
withstand. It is indeed difficult to see how living reefs could successfuUy
retreat before such forces. Once the powers of erosion gained the upper
hand, the living reef surface would be breached and damage would be
progressive and irrevocable. As suggested earlier, obeervation of the
C. M. YONOE
circulated. There is much evidence that the most actively growing
corals are those some metres below the surfon the windward side.
They have the major responsibility for maintaining the stability of the
entire atoll against the constant battering of trade wind sem. This
involves constant replacement of eroded or damaged surf-.
With
the zooxanthellae of essential assistance in maintaining a high rate of
calcification, there must also be a constant supply of food in the form of
zooplankton if only to replace the organic matter continually being lost,
carried around the atoll or dropped into profound depths. There. can be
no closed or autotrophic system in this environment. Although this is
the most difficult of all coral reef environments to penetrate, every
endeavour should be made to sample its waters and obtain some
estimate of the amount of zooplankton, largely no doubt some distance
below the surface, which is carried against these seaward reef surfaces.
The position of the partly downward directed ourrents containing this
essential zooplankton is indicated in Fig. 17, A.
We are thus brought logically to the supreme question which ariws
in any consideration of the biology of coral reefs, namely t o what
extent are the powers of growth capable of withstanding the full force
of the sea; in other words, are modern reefs static, advancing or
retreating? It has long been the opinion of the writer (Yonge, 1940)
that seaward reefs do grow outwards against constant forces of wind
and sea which mould their form. This is the opinion of Kuenen (1960),
and also of Crossland (1962) who makes the point that " Permanent
beds of living coral can exist only immediately along an outgrowing
reef where their foundations are being continually extended." Emery
et al. (1954) consider that the windward reeh at Bikini a p p r to be
growing seaward. Newell (1956), on the other hand, considera that the
seaward reefs at Raroia are getting narrower and that the surge o h e l s
are. formed by erosion, i.e. in opposition to the more general view that it
is the intervening algal ridges which are growing outwards.
By placing permanent marks on reef surfaces it should not be
difficult to discover precisely what is happening. But certainly in the
past the associated powers of growth and high calcification rate have
permitted the formation of reefs exposed to the full force of oceanic
seas. Munk and Sargent (1954) estimate that the wave% beating against
the windward reefs a t Bikini dissipate a force of approximately half a
million horsepower which the ridges and surge channels sucoe~ully
withstand. It is indeed difficult to see how living reefs could successfuUy
retreat before such forces. Once the powers of erosion gained the upper
hand, the living reef surface would be breached and damage would be
progressive and irrevocable. As suggested earlier, obeervation of the