and 0.2 kya (Tjia, 1996). Finally, there are geologic features caused by events within recent human memory. For
example, the major earthquake of March 2005 lifted reefs
off the east coast of the island of Nias by >2 m, and sunk
those on its west coast by $0.25 m (Briggs et al., 2006).
Living reefs
Indonesia’s coral reefs include all the major morphological forms: viz. atolls, barrier reefs, patch reefs, and fringing reefs (Tomascik et al., 1997). There are also coral
communities (no tendency for reef development) and
incipient reefs (which do accrete framework, but have
not yet built substantive framework; see entry Coral Reef,
Definition) on most coastal hard substrata (fluvial bars;
rocky shores). Coral communities and incipient reefs
occur on stable shores of active volcanoes (Tomascik
et al., 1996; Starger et al., 2010), while true fringing reefs
and barrier reefs occur only on non-volcanic islands and
older quiescent volcanoes. Indonesia’s “atolls” (annular
forms with enclosed lagoon) occur in the currently tectonically active Banda Sea (Figure 1a), but many are probably
sitting on non-volcanic basements. There is a preponderance of uplifted reefs in the area that suggests that over geological time scales, Indonesia’s atoll basements are
frequently subject to diastrophic deformation (Tomascik
et al., 1997). Indonesian atolls may be examples of those
for which Purdy and Winterer (2000) invoke dissolution
caused by annual monsoon rains as major drivers of lagoon
depths. The process is highly plausible for atolls in Indonesia, whose antecedent foundations would have been
exposed during LGM to annual rainfall presumably measured in meters (assuming, after Purdy and Winterer
(2000) that today’s rainfall is a good proxy for LGM rainfall). In this regard, Indonesia’s atolls contrast both with
Darwin’s classic genetic sequence of atoll formation (which
does not rely on massive dissolution), and with Grigg’s
(1982) Darwin Point elaboration, (which involves plate
movement into less hospitable waters (see entries Darwin,
Charles (1809–1882); Darwin Point; Subsidence Hypotheses of Reef Development and Volcanic Loading and Isostasy)). In Indonesia, reef development also occurs in
turbid waters along some open sedimentary coastlines,
within muddy coastal embayments, and around high continental islands. In these situations, frequently in shallowwater (5–20 m) depths, reef growth can be very rapid, with
reefs reaching sea level and undergoing significant seaward
progradation over century to millennial time scales (see
entry Turbid Zone and Terrigenous Sediment Influenced
Reefs).
Sumatra
The wave-exposed west-facing coasts of Sumatra facing
the Indian Ocean (Figure 1a) are characterized by steep
headlands and intervening beach-ridge coastal plains and
deeply incised river valleys (Richmond et al., 2006).
There are patchy fringing coral reefs in coastal bays and
nearshore continental islands, but much stronger reef
growth occurs on the continental islands that extend
in a line from Simeulue, through Nias, Banyak, Batu,
and Mentawai Islands. These islands are separated from
Sumatra by marine basins 1–2 km deep, and all have
substantial fringing coral reefs. On open west-facing
coasts, these reefs are usually patchy and narrow, but
semi-enclosed bays on all sides, and on points that deflect
ocean waves, they are up to several hundred meters wide.
A few kilometers to the west of Nias on the 200 m isobath
are the inhabited Hinako Islands (low, vegetated raised
coral reefs with wide reefs; Figure 3c). At Sumatra’s
northern tip, modest fringing reefs are developed on continental islands of Pulau Aceh and Pulau Weh. However,
reefs are absent from the entire 1,700 km of Sumatra’s
north and north-east facing coasts, which are mainly
muddy prograding shores with mangrove forests. There
are well-developed fringing reefs in the islands of the Riau
Archipelago and Natuna Sea, between Sumatra and
Kalimantan.
Java
Java’s reefs primarily comprise coral cays and island
fringing reefs offshore from its muddy north coast. The
700 reefs of Kepaluan Seribu, 20–80 km offshore from
Jakarta, are coral cays. These reefs are characterized by
a gradient of increasing coral diversity and water clarity
with increasing distance offshore (DeVantier et al.,
1995). The Karimunjawa group (70 islands about 80 km
offshore from central Java), are high islands with welldeveloped fringing reefs, barriers, and lagoons. There are
reefs scattered along the 800 km south coast of Java,
favoring points where waves approach at oblique angles.
Limited reef-flat development elsewhere along this shore
is probably a result of extremely strong waves (Spalding
et al., 2001). However there are well-developed fringing
reefs along Java’s short and more sheltered east coast
(Spalding et al., 2001).
Kalimantan
The Mahakam River, which drains almost one third of East
Kalimantan, is a major influence on reef distribution. On
the east coast, there are only occasional fringing reefs
and offshore patch reefs, for example, in front of Balikpapan Bay. Immediately to the north of the Mahakam Delta,
there are well-developed fringing reefs, interrupted by
other rivers, while northwards to the border with Sabah
the coastline is reefless, dominated by major river deltas.
The southwestern coast of South Kalimantan is also
largely deltaic and devoid of reefs, but to the east and north
of Tanjung Selatan there is some fringing-reef development. There are three barrier-reef systems east of Kalimantan: the submerged Great Sunda Barrier Reef (630 km) lies
60 km offshore along the 200 m isobath, and smaller barrier reefs are found north of the Mahakam delta. North of
the Mangkalihat Peninsula and 60 km offshore are three
major lagoonal shelf reefs: Muaras (288 km
2
), Maratua
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INDONESIAN REEFS
example, the major earthquake of March 2005 lifted reefs
off the east coast of the island of Nias by >2 m, and sunk
those on its west coast by $0.25 m (Briggs et al., 2006).
Living reefs
Indonesia’s coral reefs include all the major morphological forms: viz. atolls, barrier reefs, patch reefs, and fringing reefs (Tomascik et al., 1997). There are also coral
communities (no tendency for reef development) and
incipient reefs (which do accrete framework, but have
not yet built substantive framework; see entry Coral Reef,
Definition) on most coastal hard substrata (fluvial bars;
rocky shores). Coral communities and incipient reefs
occur on stable shores of active volcanoes (Tomascik
et al., 1996; Starger et al., 2010), while true fringing reefs
and barrier reefs occur only on non-volcanic islands and
older quiescent volcanoes. Indonesia’s “atolls” (annular
forms with enclosed lagoon) occur in the currently tectonically active Banda Sea (Figure 1a), but many are probably
sitting on non-volcanic basements. There is a preponderance of uplifted reefs in the area that suggests that over geological time scales, Indonesia’s atoll basements are
frequently subject to diastrophic deformation (Tomascik
et al., 1997). Indonesian atolls may be examples of those
for which Purdy and Winterer (2000) invoke dissolution
caused by annual monsoon rains as major drivers of lagoon
depths. The process is highly plausible for atolls in Indonesia, whose antecedent foundations would have been
exposed during LGM to annual rainfall presumably measured in meters (assuming, after Purdy and Winterer
(2000) that today’s rainfall is a good proxy for LGM rainfall). In this regard, Indonesia’s atolls contrast both with
Darwin’s classic genetic sequence of atoll formation (which
does not rely on massive dissolution), and with Grigg’s
(1982) Darwin Point elaboration, (which involves plate
movement into less hospitable waters (see entries Darwin,
Charles (1809–1882); Darwin Point; Subsidence Hypotheses of Reef Development and Volcanic Loading and Isostasy)). In Indonesia, reef development also occurs in
turbid waters along some open sedimentary coastlines,
within muddy coastal embayments, and around high continental islands. In these situations, frequently in shallowwater (5–20 m) depths, reef growth can be very rapid, with
reefs reaching sea level and undergoing significant seaward
progradation over century to millennial time scales (see
entry Turbid Zone and Terrigenous Sediment Influenced
Reefs).
Sumatra
The wave-exposed west-facing coasts of Sumatra facing
the Indian Ocean (Figure 1a) are characterized by steep
headlands and intervening beach-ridge coastal plains and
deeply incised river valleys (Richmond et al., 2006).
There are patchy fringing coral reefs in coastal bays and
nearshore continental islands, but much stronger reef
growth occurs on the continental islands that extend
in a line from Simeulue, through Nias, Banyak, Batu,
and Mentawai Islands. These islands are separated from
Sumatra by marine basins 1–2 km deep, and all have
substantial fringing coral reefs. On open west-facing
coasts, these reefs are usually patchy and narrow, but
semi-enclosed bays on all sides, and on points that deflect
ocean waves, they are up to several hundred meters wide.
A few kilometers to the west of Nias on the 200 m isobath
are the inhabited Hinako Islands (low, vegetated raised
coral reefs with wide reefs; Figure 3c). At Sumatra’s
northern tip, modest fringing reefs are developed on continental islands of Pulau Aceh and Pulau Weh. However,
reefs are absent from the entire 1,700 km of Sumatra’s
north and north-east facing coasts, which are mainly
muddy prograding shores with mangrove forests. There
are well-developed fringing reefs in the islands of the Riau
Archipelago and Natuna Sea, between Sumatra and
Kalimantan.
Java
Java’s reefs primarily comprise coral cays and island
fringing reefs offshore from its muddy north coast. The
700 reefs of Kepaluan Seribu, 20–80 km offshore from
Jakarta, are coral cays. These reefs are characterized by
a gradient of increasing coral diversity and water clarity
with increasing distance offshore (DeVantier et al.,
1995). The Karimunjawa group (70 islands about 80 km
offshore from central Java), are high islands with welldeveloped fringing reefs, barriers, and lagoons. There are
reefs scattered along the 800 km south coast of Java,
favoring points where waves approach at oblique angles.
Limited reef-flat development elsewhere along this shore
is probably a result of extremely strong waves (Spalding
et al., 2001). However there are well-developed fringing
reefs along Java’s short and more sheltered east coast
(Spalding et al., 2001).
Kalimantan
The Mahakam River, which drains almost one third of East
Kalimantan, is a major influence on reef distribution. On
the east coast, there are only occasional fringing reefs
and offshore patch reefs, for example, in front of Balikpapan Bay. Immediately to the north of the Mahakam Delta,
there are well-developed fringing reefs, interrupted by
other rivers, while northwards to the border with Sabah
the coastline is reefless, dominated by major river deltas.
The southwestern coast of South Kalimantan is also
largely deltaic and devoid of reefs, but to the east and north
of Tanjung Selatan there is some fringing-reef development. There are three barrier-reef systems east of Kalimantan: the submerged Great Sunda Barrier Reef (630 km) lies
60 km offshore along the 200 m isobath, and smaller barrier reefs are found north of the Mahakam delta. North of
the Mangkalihat Peninsula and 60 km offshore are three
major lagoonal shelf reefs: Muaras (288 km
2
), Maratua
598
INDONESIAN REEFS