360
WORLD ATLAS OF CORAL REEFS
Marshall Islands
MAP 13d
The
Marshall Islands are a complex of 28 coral atolls
and 5 small (non-atolll islands lying in two broad
chains, the eastern Ratak (sunrise) chain and the
western Ralik (sunset) chain. The isolated atolls of
Enewetak and Ujelang lie to the west of these main chains.
Wake Atoll, to the north, is clearly linked to this group
biologically and geologically, but is separately administered by the USA (see Chapter 14). In all there are some
1
136 islands dispersed over a vast area of ocean, although
the total land area is very small. The atolls are typically
circular to elliptical with shallow lagoons. Kwajalein, at
some 2 500 square kilometers, is the largest atoll in the
Pacific. The two chains were probably formed by plate
movement over a volcanic hotspot, although there is no
current volcanic activity. Deep drilling into the reefs of
Bikini and Enewetak atolls revealed a sequence of reef
deposits ranging from 1.3 to 1.4 kilometers thick overlying basalt rock from the original volcanic activity.
Dating work on the fossils at the base of these, together
with the youngest basalt rock below, indicated that this
volcanic activity occurred 50-59 million years ago. All
of the islands lie close to sea level with a mean height
of about 2 meters.
The climate varies from north to south. In the south,
10 km
rainfall is relatively high and winds are dominated by
the northeast trade winds from December to April and by
the southeast trades from May to November. To the north,
the northeast trade winds dominate all year round, and
typhoons are more common. Six have hit the islands since
1900. some with severe impacts. There is a westerly
flowing Equatorial Current north of about 9°N and south
of 4°N, but between these latitudes there is the easterly
flowing Equatorial Counter Current.
The location of the Marshall Islands places them in
an area of fairly high diversity, while the relative lack of
pressure on many of the reefs means that there has been
little biodiversity loss. Nearly 250 coral species have been
recorded at Bikini Atoll, and over 250 species of reef fish
are noted. A detailed study of marine algae undertaken
in the 1950s revealed some 238 species. Mangroves are
also found in the islands, but are not common or diverse.
There are important seabird populations, particularly in the
northern atolls, with at least 15 breeding species among
the 3 1 recorded in the islands. Some 27 species of whale
and dolphin have also been recorded.
Politically the Marshall Islands form an independent
state, but exist in a "free association" with the USA. Two
thirds of the population live on Majuro and Ebeye where
Bikini Atolt, with the crater in the reef fiat from a nuclear test dearly visible in the lagoon edge of the reef flat to the
northwest IST5055-96-5. 19931.
WORLD ATLAS OF CORAL REEFS
Marshall Islands
MAP 13d
The
Marshall Islands are a complex of 28 coral atolls
and 5 small (non-atolll islands lying in two broad
chains, the eastern Ratak (sunrise) chain and the
western Ralik (sunset) chain. The isolated atolls of
Enewetak and Ujelang lie to the west of these main chains.
Wake Atoll, to the north, is clearly linked to this group
biologically and geologically, but is separately administered by the USA (see Chapter 14). In all there are some
1
136 islands dispersed over a vast area of ocean, although
the total land area is very small. The atolls are typically
circular to elliptical with shallow lagoons. Kwajalein, at
some 2 500 square kilometers, is the largest atoll in the
Pacific. The two chains were probably formed by plate
movement over a volcanic hotspot, although there is no
current volcanic activity. Deep drilling into the reefs of
Bikini and Enewetak atolls revealed a sequence of reef
deposits ranging from 1.3 to 1.4 kilometers thick overlying basalt rock from the original volcanic activity.
Dating work on the fossils at the base of these, together
with the youngest basalt rock below, indicated that this
volcanic activity occurred 50-59 million years ago. All
of the islands lie close to sea level with a mean height
of about 2 meters.
The climate varies from north to south. In the south,
10 km
rainfall is relatively high and winds are dominated by
the northeast trade winds from December to April and by
the southeast trades from May to November. To the north,
the northeast trade winds dominate all year round, and
typhoons are more common. Six have hit the islands since
1900. some with severe impacts. There is a westerly
flowing Equatorial Current north of about 9°N and south
of 4°N, but between these latitudes there is the easterly
flowing Equatorial Counter Current.
The location of the Marshall Islands places them in
an area of fairly high diversity, while the relative lack of
pressure on many of the reefs means that there has been
little biodiversity loss. Nearly 250 coral species have been
recorded at Bikini Atoll, and over 250 species of reef fish
are noted. A detailed study of marine algae undertaken
in the 1950s revealed some 238 species. Mangroves are
also found in the islands, but are not common or diverse.
There are important seabird populations, particularly in the
northern atolls, with at least 15 breeding species among
the 3 1 recorded in the islands. Some 27 species of whale
and dolphin have also been recorded.
Politically the Marshall Islands form an independent
state, but exist in a "free association" with the USA. Two
thirds of the population live on Majuro and Ebeye where
Bikini Atolt, with the crater in the reef fiat from a nuclear test dearly visible in the lagoon edge of the reef flat to the
northwest IST5055-96-5. 19931.