of a way out of the bewildering complexity of the “labyrinth” of submerged reefs created a sensation. He published his description of the impact and the beaching of
the vessel for repairs. Once safe in the ocean, Cook wrote
one of the most powerful coral reef images ever: “A Reef
such as is here spoke of is scarcely known in Europe, it is
a wall of Coral Rock rising all most perpendicular out of
the unfathomable Ocean. . . the large waves of the vast
Ocean meeting with so sudden a resistance make
a most terrible surf, breaking mountains high.”
In 1770, after his encounter with the Great Barrier
Reef, Cook had become aware of a major scientific controversy among European and British naturalists that in
some mysterious way coral reefs were built neither by
rocks nor by petrified plants as 2,000 years of tradition
had supposed, but were the production of microscopically small animals, then part of the extensive range of
unknown, unclassified organisms collectively termed
“insects”.
Barely 4 years later, during his second 1772–1775
exploratory voyage in the Pacific in command of the Resolution, as he navigated past continental islands in the central Pacific with elevated relict fringing reefs, he recorded
in his Journal for June 1774 his puzzlement “If these
Coral rockes were first formed in the Sea by animals,
how came they thrown up, to such a height? Has this
Island been raised by an Earth quake or has the sea receded
from it? Some philosophers [scientists] have attempted to
account for the formation of low isles such as are in this
Sea, but I do not know of any thing has been said of high
Islands or such as I have been speaking of,” thereby providing speculation for further reef research.
Bibliography
Bowen, J., 2002. The Great Barrier Reef: History, Science,
Heritage. Cambridge: Cambridge University Press.
Cook, J., 1770–1771. In Beaglehole, J. C. (ed.) 1955. Repr. 1968,
The Voyage of the Endeavour 1768–1771. Cambridge:
Cambridge University Press for the Hakluyt Society.
CORAL CAY CLASSIFICATION AND EVOLUTION
Scott G. Smithers, David Hopley
James Cook University, QLD, Townsville, Australia
Definition
A coral cay is an island formed from sediments derived
from the reef on which it sits and swept by refracted waves
to a focal point on the reef flat where they are deposited.
A cay initially may remain intertidal and lack vegetation,
but with time it is likely to build up to be above sea
level, acquire a vegetation cover, and become partially
lithified.
Introduction
Islands associated with coral reefs have been occupied or
used by humans for millennia. They became known to
western society as voyages of discovery crossed tropical
waters. A distinction has been made between “high”
islands composed of continental rocks and “low” islands
of biogenic carbonate sediments produced by reef organisms. The variety of morphologies that were observed
became a focus of early studies:
“There are different opinions amongst ingenious theorists,
concerning the formation of such low islands”.
(James Cook, 17 April, 1777)
Scientific studies of reef islands were first made in the
nineteenth century in south-east Asia and the Australian
Great Barrier Reef (GBR) and subsequently in the Pacific
and Indian Oceans and in the Caribbean Sea (see Table 1;
Stoddart and Steers, 1977) (see Steers, James Alfred
(1899–1987); Stoddart, David Ross (1937–)).
As the diversity of form became evident, various
attempts at classification were undertaken. More recently
research has extended to understand processes that form
and maintain coral cays and their origin, age, and evolution. Many of these investigations, especially the development of classifications, were based on studies of the GBR
(Spender, 1930; Steers, 1929, 1938; Fairbridge, 1950;
Stoddart and Steers, 1977; Hopley, 1982, 1997; Hopley
et al., 2007). The GBR is the largest reef province in the
world, which when combined with the adjacent Torres
Strait contains over 1,000 islands including approximately
350 coral cays (Hopley et al., 2007). Stretching over 15
of latitude and with reefs extending from the mainland to
the shelf edge, the GBR provides a diversity of environments which are responsible for the great variety of coral
cay types found within its waters (see entry:
Section 10.1.3 in Hopley et al., 2007).
Cay formation: wave influences
Coral cays generally occur on reef flats at or very close to
sea level. The reef flat need not be large (many occur on
small reefs <1 km
2
), and some sand cays in the Maldives
have been shown to develop over lagoonal sediments
while the reef flat is still evolving (Kench et al., 2005).
A supply of biogenic sediments is fundamental for cay formation, but most reef tops have partial veneers of sand and
shingle and there are many with diffuse sediment sheets
that remain unconcentrated. The most critical factor for
cay formation is the centripetal pattern of sediment movement produced by waves and currents in response to reef
shape; centripetal sediment transport delivers sediment
to a focal point or depositional node where it may accumulate (see Hydrodynamics of Coral Reef Systems; Wave
Shoaling and Refraction; Waves and Wave Driven
Currents).
Two related features of wave transformation over a reef
control whether or not deposition is spatially concentrated.
The first is the convergence of waves. The depth of water
just beyond the reef front means that waves do not fully
CORAL CAY CLASSIFICATION AND EVOLUTION
237
the vessel for repairs. Once safe in the ocean, Cook wrote
one of the most powerful coral reef images ever: “A Reef
such as is here spoke of is scarcely known in Europe, it is
a wall of Coral Rock rising all most perpendicular out of
the unfathomable Ocean. . . the large waves of the vast
Ocean meeting with so sudden a resistance make
a most terrible surf, breaking mountains high.”
In 1770, after his encounter with the Great Barrier
Reef, Cook had become aware of a major scientific controversy among European and British naturalists that in
some mysterious way coral reefs were built neither by
rocks nor by petrified plants as 2,000 years of tradition
had supposed, but were the production of microscopically small animals, then part of the extensive range of
unknown, unclassified organisms collectively termed
“insects”.
Barely 4 years later, during his second 1772–1775
exploratory voyage in the Pacific in command of the Resolution, as he navigated past continental islands in the central Pacific with elevated relict fringing reefs, he recorded
in his Journal for June 1774 his puzzlement “If these
Coral rockes were first formed in the Sea by animals,
how came they thrown up, to such a height? Has this
Island been raised by an Earth quake or has the sea receded
from it? Some philosophers [scientists] have attempted to
account for the formation of low isles such as are in this
Sea, but I do not know of any thing has been said of high
Islands or such as I have been speaking of,” thereby providing speculation for further reef research.
Bibliography
Bowen, J., 2002. The Great Barrier Reef: History, Science,
Heritage. Cambridge: Cambridge University Press.
Cook, J., 1770–1771. In Beaglehole, J. C. (ed.) 1955. Repr. 1968,
The Voyage of the Endeavour 1768–1771. Cambridge:
Cambridge University Press for the Hakluyt Society.
CORAL CAY CLASSIFICATION AND EVOLUTION
Scott G. Smithers, David Hopley
James Cook University, QLD, Townsville, Australia
Definition
A coral cay is an island formed from sediments derived
from the reef on which it sits and swept by refracted waves
to a focal point on the reef flat where they are deposited.
A cay initially may remain intertidal and lack vegetation,
but with time it is likely to build up to be above sea
level, acquire a vegetation cover, and become partially
lithified.
Introduction
Islands associated with coral reefs have been occupied or
used by humans for millennia. They became known to
western society as voyages of discovery crossed tropical
waters. A distinction has been made between “high”
islands composed of continental rocks and “low” islands
of biogenic carbonate sediments produced by reef organisms. The variety of morphologies that were observed
became a focus of early studies:
“There are different opinions amongst ingenious theorists,
concerning the formation of such low islands”.
(James Cook, 17 April, 1777)
Scientific studies of reef islands were first made in the
nineteenth century in south-east Asia and the Australian
Great Barrier Reef (GBR) and subsequently in the Pacific
and Indian Oceans and in the Caribbean Sea (see Table 1;
Stoddart and Steers, 1977) (see Steers, James Alfred
(1899–1987); Stoddart, David Ross (1937–)).
As the diversity of form became evident, various
attempts at classification were undertaken. More recently
research has extended to understand processes that form
and maintain coral cays and their origin, age, and evolution. Many of these investigations, especially the development of classifications, were based on studies of the GBR
(Spender, 1930; Steers, 1929, 1938; Fairbridge, 1950;
Stoddart and Steers, 1977; Hopley, 1982, 1997; Hopley
et al., 2007). The GBR is the largest reef province in the
world, which when combined with the adjacent Torres
Strait contains over 1,000 islands including approximately
350 coral cays (Hopley et al., 2007). Stretching over 15
of latitude and with reefs extending from the mainland to
the shelf edge, the GBR provides a diversity of environments which are responsible for the great variety of coral
cay types found within its waters (see entry:
Section 10.1.3 in Hopley et al., 2007).
Cay formation: wave influences
Coral cays generally occur on reef flats at or very close to
sea level. The reef flat need not be large (many occur on
small reefs <1 km
2
), and some sand cays in the Maldives
have been shown to develop over lagoonal sediments
while the reef flat is still evolving (Kench et al., 2005).
A supply of biogenic sediments is fundamental for cay formation, but most reef tops have partial veneers of sand and
shingle and there are many with diffuse sediment sheets
that remain unconcentrated. The most critical factor for
cay formation is the centripetal pattern of sediment movement produced by waves and currents in response to reef
shape; centripetal sediment transport delivers sediment
to a focal point or depositional node where it may accumulate (see Hydrodynamics of Coral Reef Systems; Wave
Shoaling and Refraction; Waves and Wave Driven
Currents).
Two related features of wave transformation over a reef
control whether or not deposition is spatially concentrated.
The first is the convergence of waves. The depth of water
just beyond the reef front means that waves do not fully
CORAL CAY CLASSIFICATION AND EVOLUTION
237