220
C . M. YONGE
previous observations on the influence of trade winds on the configuration of reefs (see Yonge, 1951). The often striking differences
between windward and leeward reefs were clearly demonstrated by the
Dutch surveys in East Indian waters which have been summarized by
Umbgrove (1947). In more intimate detail, at Low Isles and elsewhere,
they are described in the reports of the Great Barrier Reef Expedition.
The wide diversity of ecological niches on coral reefs has been revealed.
This is even greater on atolls where in addition to exposed and sheltered
outer shores (NE and SE and SW and NW respectively north and south
of the equator) there is the enclosed lagoon with its exposed and shel'tered shores (here SW and NW and NE and SE respectively). The
consequent further increased environmental complexity influences the
distribution of corals and other reef organisms. There can be no region
of comparable size in the sea with such a diversity of ecological niches
aa an atoll.
The first stage in the analysis of such conditions must be descriptive.
The geological background to Bikini and adjacent atolls has been
provided by Tracey et at. (1948), Ladd et al. (1953) and Emery et al.
(1954) while Munk and Sargent (1954) have described the interactions
between the growth of the living reef surface and the force of the waves,
The major biological survey is by Wells (1954) and can be only briefly
summarized.
Viewed in section, as shown in Fig. 1, these Pacific atolls may be
divided into the following regions (Tracey et al., 1955) starting from the
windward. (1) The outer seaward slope with a pronounced reduction in
corals and coralline algae below about 10 fathoms. (2) A rshallow
'' sublittoral " region with more gradual slope, rich coral population and
often locally terraced. (3) The seaward reef margin with its dgd ridge
of Pwolithun (= Lithothamnion) and characteristic surge channels (in
region indicated by x). (4, 5) An outer and an inner reef flat with
characteristic zones of coral population described below. (6) The
seaward beach of the island, usually buttressed with beach rock. (7) The
more sheltered lagoon beach. (8) The shallow lagoon reef flat or lagoon
shelf. (9) The lagoon reef margin. (10) The sheltered lagoon slope.
(11) The lagoon floor. (12) Coral knolls or pinnacles (patch reefs) that
rise in great numbers from the flat lagoon floor which is itself oharactenstically covered with the green calcareous weed Halimeda. Intense
echo sounding has revealed the great abundance. of these coral r n m ,
over 2000 in the 24-mile-long lagoon at Eniwetok (Emery, 1948).
(13) The more irregular and richer expoaed lagoon slop leading to
the lagoon reef margin (14). (16) The reef flat on the leeward side.
(16) The seaward reef margin here without an algal ridge and surge
C . M. YONGE
previous observations on the influence of trade winds on the configuration of reefs (see Yonge, 1951). The often striking differences
between windward and leeward reefs were clearly demonstrated by the
Dutch surveys in East Indian waters which have been summarized by
Umbgrove (1947). In more intimate detail, at Low Isles and elsewhere,
they are described in the reports of the Great Barrier Reef Expedition.
The wide diversity of ecological niches on coral reefs has been revealed.
This is even greater on atolls where in addition to exposed and sheltered
outer shores (NE and SE and SW and NW respectively north and south
of the equator) there is the enclosed lagoon with its exposed and shel'tered shores (here SW and NW and NE and SE respectively). The
consequent further increased environmental complexity influences the
distribution of corals and other reef organisms. There can be no region
of comparable size in the sea with such a diversity of ecological niches
aa an atoll.
The first stage in the analysis of such conditions must be descriptive.
The geological background to Bikini and adjacent atolls has been
provided by Tracey et at. (1948), Ladd et al. (1953) and Emery et al.
(1954) while Munk and Sargent (1954) have described the interactions
between the growth of the living reef surface and the force of the waves,
The major biological survey is by Wells (1954) and can be only briefly
summarized.
Viewed in section, as shown in Fig. 1, these Pacific atolls may be
divided into the following regions (Tracey et al., 1955) starting from the
windward. (1) The outer seaward slope with a pronounced reduction in
corals and coralline algae below about 10 fathoms. (2) A rshallow
'' sublittoral " region with more gradual slope, rich coral population and
often locally terraced. (3) The seaward reef margin with its dgd ridge
of Pwolithun (= Lithothamnion) and characteristic surge channels (in
region indicated by x). (4, 5) An outer and an inner reef flat with
characteristic zones of coral population described below. (6) The
seaward beach of the island, usually buttressed with beach rock. (7) The
more sheltered lagoon beach. (8) The shallow lagoon reef flat or lagoon
shelf. (9) The lagoon reef margin. (10) The sheltered lagoon slope.
(11) The lagoon floor. (12) Coral knolls or pinnacles (patch reefs) that
rise in great numbers from the flat lagoon floor which is itself oharactenstically covered with the green calcareous weed Halimeda. Intense
echo sounding has revealed the great abundance. of these coral r n m ,
over 2000 in the 24-mile-long lagoon at Eniwetok (Emery, 1948).
(13) The more irregular and richer expoaed lagoon slop leading to
the lagoon reef margin (14). (16) The reef flat on the leeward side.
(16) The seaward reef margin here without an algal ridge and surge