THE B I O M O Y OF CORAL REEFS
225
genera and some 35 species, compared with 80 genera and about 700
species in the Indo-Pacific ”, adding that although Acropora and
Porites are the most important genera in both regions, each is represented by only three species in the Atlantic compared with 150
and thirty species respectively in the Indo-Pacific. However, in 1961,
Goreau extends the number of species, for the West Indies, to 46.
He now considers (in correspondence noted earlier) that these numbers
should be further increased.
Newell has made important comparisons between coral reefs in these
two great faunistic areas, on the basis of personal experiences at
Raroia (Newell, 1956) and in the Bahamas (Newell, 1955, 1958, 1959;
Newell et al., 1951 ; Newell and Imbrie, 1955). Unlike Pacific reefs,
those of the West Indies are seldom on the margin of the submarine
platforms from which they rise and which Newell thinks were probably
formed by erosion during periods of low sea level in the Pleistocene.
The reefs appear immature, seldom reaching the surface and being
largely confined to more favourable, i.e. windward, are-. 0 -
to the
long continued coolness of the West Atlantic during the Quaternary
when conditions in the Indo-Pacific were tropical, the re-establishment
of reefs was longer delayed and Newell does not think that West Indian
reefs are more than between 3000 and 6000 years old. But they are
situated on extensive platforms bounded by precipitous escarpments
which very probably represent coral formations possibly originating as
far back as the Jurassic and only finally killed off in the glacial periods
of the Pleistocene.
Diagrams illustrating Newell’s comparison between Weat Indian
(A) and Pacific (B) reefs are shown in Fig. 6. The seaward slopes in
the former are more gradual but in both he identifim a deeper ‘‘ mushroom zone ” (1) and a higher “ elkhorn zone ” (2) whioh reaohes the
always submerged reef crest in A. An algal ridge (3) which breaks the
surface at low water of spring tides (the level shown in the figure) with
its enclosed reef flat (4) is present only in B. What corresponds in A to
the latter region but is continually submerged forms an extensive
lagoon ( 5 ) much reduced in B. Recent corals form no more than a
veneer over the older rocks (shown stippIed) in A ; this rock has been
extemively increased by such coral in B (heavier stipple).
Goreau (1959b), in the first of a series of contributions which will
greatly widen our knowledge, has given a detailed description of a
fringing barrier formation (typical of many such) off the northern coast
of Jamaica, i.e. on the weather side facing the NE trades. All is
effectively submerged. By surface examination and by diving he
divides the reef into the following series of zones (Fig. 7). (1) A s h e
225
genera and some 35 species, compared with 80 genera and about 700
species in the Indo-Pacific ”, adding that although Acropora and
Porites are the most important genera in both regions, each is represented by only three species in the Atlantic compared with 150
and thirty species respectively in the Indo-Pacific. However, in 1961,
Goreau extends the number of species, for the West Indies, to 46.
He now considers (in correspondence noted earlier) that these numbers
should be further increased.
Newell has made important comparisons between coral reefs in these
two great faunistic areas, on the basis of personal experiences at
Raroia (Newell, 1956) and in the Bahamas (Newell, 1955, 1958, 1959;
Newell et al., 1951 ; Newell and Imbrie, 1955). Unlike Pacific reefs,
those of the West Indies are seldom on the margin of the submarine
platforms from which they rise and which Newell thinks were probably
formed by erosion during periods of low sea level in the Pleistocene.
The reefs appear immature, seldom reaching the surface and being
largely confined to more favourable, i.e. windward, are-. 0 -
to the
long continued coolness of the West Atlantic during the Quaternary
when conditions in the Indo-Pacific were tropical, the re-establishment
of reefs was longer delayed and Newell does not think that West Indian
reefs are more than between 3000 and 6000 years old. But they are
situated on extensive platforms bounded by precipitous escarpments
which very probably represent coral formations possibly originating as
far back as the Jurassic and only finally killed off in the glacial periods
of the Pleistocene.
Diagrams illustrating Newell’s comparison between Weat Indian
(A) and Pacific (B) reefs are shown in Fig. 6. The seaward slopes in
the former are more gradual but in both he identifim a deeper ‘‘ mushroom zone ” (1) and a higher “ elkhorn zone ” (2) whioh reaohes the
always submerged reef crest in A. An algal ridge (3) which breaks the
surface at low water of spring tides (the level shown in the figure) with
its enclosed reef flat (4) is present only in B. What corresponds in A to
the latter region but is continually submerged forms an extensive
lagoon ( 5 ) much reduced in B. Recent corals form no more than a
veneer over the older rocks (shown stippIed) in A ; this rock has been
extemively increased by such coral in B (heavier stipple).
Goreau (1959b), in the first of a series of contributions which will
greatly widen our knowledge, has given a detailed description of a
fringing barrier formation (typical of many such) off the northern coast
of Jamaica, i.e. on the weather side facing the NE trades. All is
effectively submerged. By surface examination and by diving he
divides the reef into the following series of zones (Fig. 7). (1) A s h e