being used to adequately describe water flow and the
freshwater resource dynamics of coral cays.
Bibliography
Anthony, S. S., 1997. Hydrogeology of selected islands of the Federated States of Micronesia. In Vacher, H. L., and Quinn, T. (eds.),
Geology and Hydrology of Carbonate Islands. Amsterdam:
Elsevier, pp. 693–706.
Anthony, S. S., Peterson, F. L., Mackenzie, F. T., and Hamlin, S. N.,
1989. Geohydrology of the Laura Fresh-Water Lens, Majuro
Atoll - a hydrogeochemical approach. Geological Society of
America Bulletin, 101, 1066–1075.
Ayers, J. F., and Vacher, H. L., 1986. Hydrogeology of an atoll
island - a conceptual-model from detailed study of a Micronesian
example. Ground Water, 24, 185–198.
Bailey, R. T., Jenson, J. W., and Olsen, A. E., 2009. Numerical
modeling of atoll island hydrogeology. Ground Water, 47,
184–196.
Falkland, A. C., 1993. Hydrology and water management on small
tropical islands. In Proceedings International Symposium on
Hydrology of Warm Humid Regions. International Association
of Hydrological Sciences, pp. 263–303.
Griggs, J. E., and Peterson, F. L., 1993. Groundwater-flow dynamics and development strategies at the atoll scale. Ground Water,
31, 209–220.
Herman, M. E., Buddemeier, R. W., and Wheatcraft, S. W., 1986.
A layered aquifer model of atoll island hydrology - Validation
of a computer-simulation. Journal of Hydrology, 84, 303–322.
Hopley, D., Smithers, S. G., and Parnell, K. E., 2007. The geomorphology of the Great Barrier Reef: developmemt, diversity and
change. Cambridge: Cambridge University Press.
Oberdorfer, J. A., and Buddemeier, R. W., 1988. Climate change:
Effects on reef island resources, In Proceedings Sixth International Coral Reef Symposium, 3, 523–527.
Oberdorfer, J. A., Hogan, P. J., and Buddemeier, R. W., 1990. Atoll
island hydrogeology - Flow and fresh-water occurrence in
a tidally dominated system. Journal of Hydrology, 120, 327–340.
Underwood, M. R., Peterson, F. L., and Voss, C. I., 1992. Groundwater lens dynamics of Atoll Islands. Water Resources Research,
28, 2889–2902.
Vacher, H. L., 1997. Introducution: Varieties of carbonate islands and
a historical perspective. In Vacher, H. L., and Quinn, T. (eds.),
Geology and Hydrology of Carbonate Islands. Amsterdam:
Elsevier, pp. 1–33.
Voss, C. I., and Provost, A. M., 2003. SUTRA, A Model for
Saturated-Unsaturated Variable-Density Ground-Water Flow
with Solute or Energy Transport. Reston: USGS.
Wheatcraft, S. W., and Buddemeier, R. W., 1981. Atoll-Island
hydrology. Ground Water, 19, 311–320.
White, I., Falkland, T., Metutera, T., Metai, E., Overmars, M., Perez, P.,
and Dray, A., 2007. Climatic and human influences on groundwater in low atolls. Vadose Zone Journal, 6, 581–590.
Woodroffe, C. D., and Falkland, A. C., 1997. Geology and hydrogeology of the Cocos (Keeling) Islands. In Vacher, H. L., and
Quinn, T. (eds.), Geology and Hydrology of Carbonate Islands.
Amsterdam: Elsevier, pp. 885–908.
Cross-references
Atoll Islands (Motu)
Cay Formation
Holocene Reefs: Thickness and Characteristics
Internal Circulation
Last Glacial Lowstand and Shelf Exposure
Solution Unconformities
CORAL CAYS, VEGETATIONAL SUCCESSION
Harold Heatwole
North Caroline State University, Raleigh, NC, USA
Definition
Succession: A series of biotic communities replacing each
other in an ordered temporal sequence, with each community creating conditions leading to the establishment of its
successor.
Aeolian: Having to do with the wind.
Allochthonous: Coming from a source external to an ecosystem, community, or area.
Washover: The sea washing over an island during a storm.
Early colonization
Continental islands have vegetation similar to that of and
derived from the adjacent mainland. By contrast, cays
have a much more limited subset of mainland floras, filtered by the vagaries of overwater dispersal; however,
even for those, vegetation varies from sparse herbs, vines,
and grasses to tall, dense forests. The present treatise deals
with the causes of that variation and the temporal
sequences through which cay vegetation pass.
The course of succession on cays depends on the type of
substrate initially present. There are three main types associated with modern coral reefs. Sand cays begin as submerged sand bars that gradually accrete and eventually
emerge from the sea. Rubble (or shingle) cays are formed
suddenly by material from the reef being broken off and
heaped onto the reef flat by a storm. In both cases, bare surfaces of sand or pieces of coral are exposed subaerially
(Figure 1) and are available for colonization by terrestrial
plants and animals, via some form of over-water dispersal.
Mangrove cays differ in that plant succession begins
before the cay itself forms. Propagules of mangroves are
sea dispersed and take root in shallow water on reefs where
they grow into trees. Dead leaves and other organic debris
from these trees accumulate around the roots and eventually build up an organically rich mud that may in time
become emergent above sea level. Some islands, of
course, may be composites of more than one of these
types.
Surprisingly, the first successful colonizers of bare cays
may be animals, rather than plants. On the Great Barrier
Reef of Australia, there are a number of sand cays,
completely devoid of vegetation, that nevertheless have
a fauna of up to 11 species of terrestrial invertebrates
(Heatwole, 1971) such as flies, beetles, earwigs, mites,
and isopods that subsist on dead marine organisms washed
onto the beach, the carrion of marine intertidal invertebrates, and the excrement or cadavers of seabirds nesting
on the island. On some cays, there are, in addition, predators such as centipedes and spiders, that feed on these
terrestrial invertebrate scavengers. This assemblage
thus depends either directly or indirectly on energy and
256
CORAL CAYS, VEGETATIONAL SUCCESSION
freshwater resource dynamics of coral cays.
Bibliography
Anthony, S. S., 1997. Hydrogeology of selected islands of the Federated States of Micronesia. In Vacher, H. L., and Quinn, T. (eds.),
Geology and Hydrology of Carbonate Islands. Amsterdam:
Elsevier, pp. 693–706.
Anthony, S. S., Peterson, F. L., Mackenzie, F. T., and Hamlin, S. N.,
1989. Geohydrology of the Laura Fresh-Water Lens, Majuro
Atoll - a hydrogeochemical approach. Geological Society of
America Bulletin, 101, 1066–1075.
Ayers, J. F., and Vacher, H. L., 1986. Hydrogeology of an atoll
island - a conceptual-model from detailed study of a Micronesian
example. Ground Water, 24, 185–198.
Bailey, R. T., Jenson, J. W., and Olsen, A. E., 2009. Numerical
modeling of atoll island hydrogeology. Ground Water, 47,
184–196.
Falkland, A. C., 1993. Hydrology and water management on small
tropical islands. In Proceedings International Symposium on
Hydrology of Warm Humid Regions. International Association
of Hydrological Sciences, pp. 263–303.
Griggs, J. E., and Peterson, F. L., 1993. Groundwater-flow dynamics and development strategies at the atoll scale. Ground Water,
31, 209–220.
Herman, M. E., Buddemeier, R. W., and Wheatcraft, S. W., 1986.
A layered aquifer model of atoll island hydrology - Validation
of a computer-simulation. Journal of Hydrology, 84, 303–322.
Hopley, D., Smithers, S. G., and Parnell, K. E., 2007. The geomorphology of the Great Barrier Reef: developmemt, diversity and
change. Cambridge: Cambridge University Press.
Oberdorfer, J. A., and Buddemeier, R. W., 1988. Climate change:
Effects on reef island resources, In Proceedings Sixth International Coral Reef Symposium, 3, 523–527.
Oberdorfer, J. A., Hogan, P. J., and Buddemeier, R. W., 1990. Atoll
island hydrogeology - Flow and fresh-water occurrence in
a tidally dominated system. Journal of Hydrology, 120, 327–340.
Underwood, M. R., Peterson, F. L., and Voss, C. I., 1992. Groundwater lens dynamics of Atoll Islands. Water Resources Research,
28, 2889–2902.
Vacher, H. L., 1997. Introducution: Varieties of carbonate islands and
a historical perspective. In Vacher, H. L., and Quinn, T. (eds.),
Geology and Hydrology of Carbonate Islands. Amsterdam:
Elsevier, pp. 1–33.
Voss, C. I., and Provost, A. M., 2003. SUTRA, A Model for
Saturated-Unsaturated Variable-Density Ground-Water Flow
with Solute or Energy Transport. Reston: USGS.
Wheatcraft, S. W., and Buddemeier, R. W., 1981. Atoll-Island
hydrology. Ground Water, 19, 311–320.
White, I., Falkland, T., Metutera, T., Metai, E., Overmars, M., Perez, P.,
and Dray, A., 2007. Climatic and human influences on groundwater in low atolls. Vadose Zone Journal, 6, 581–590.
Woodroffe, C. D., and Falkland, A. C., 1997. Geology and hydrogeology of the Cocos (Keeling) Islands. In Vacher, H. L., and
Quinn, T. (eds.), Geology and Hydrology of Carbonate Islands.
Amsterdam: Elsevier, pp. 885–908.
Cross-references
Atoll Islands (Motu)
Cay Formation
Holocene Reefs: Thickness and Characteristics
Internal Circulation
Last Glacial Lowstand and Shelf Exposure
Solution Unconformities
CORAL CAYS, VEGETATIONAL SUCCESSION
Harold Heatwole
North Caroline State University, Raleigh, NC, USA
Definition
Succession: A series of biotic communities replacing each
other in an ordered temporal sequence, with each community creating conditions leading to the establishment of its
successor.
Aeolian: Having to do with the wind.
Allochthonous: Coming from a source external to an ecosystem, community, or area.
Washover: The sea washing over an island during a storm.
Early colonization
Continental islands have vegetation similar to that of and
derived from the adjacent mainland. By contrast, cays
have a much more limited subset of mainland floras, filtered by the vagaries of overwater dispersal; however,
even for those, vegetation varies from sparse herbs, vines,
and grasses to tall, dense forests. The present treatise deals
with the causes of that variation and the temporal
sequences through which cay vegetation pass.
The course of succession on cays depends on the type of
substrate initially present. There are three main types associated with modern coral reefs. Sand cays begin as submerged sand bars that gradually accrete and eventually
emerge from the sea. Rubble (or shingle) cays are formed
suddenly by material from the reef being broken off and
heaped onto the reef flat by a storm. In both cases, bare surfaces of sand or pieces of coral are exposed subaerially
(Figure 1) and are available for colonization by terrestrial
plants and animals, via some form of over-water dispersal.
Mangrove cays differ in that plant succession begins
before the cay itself forms. Propagules of mangroves are
sea dispersed and take root in shallow water on reefs where
they grow into trees. Dead leaves and other organic debris
from these trees accumulate around the roots and eventually build up an organically rich mud that may in time
become emergent above sea level. Some islands, of
course, may be composites of more than one of these
types.
Surprisingly, the first successful colonizers of bare cays
may be animals, rather than plants. On the Great Barrier
Reef of Australia, there are a number of sand cays,
completely devoid of vegetation, that nevertheless have
a fauna of up to 11 species of terrestrial invertebrates
(Heatwole, 1971) such as flies, beetles, earwigs, mites,
and isopods that subsist on dead marine organisms washed
onto the beach, the carrion of marine intertidal invertebrates, and the excrement or cadavers of seabirds nesting
on the island. On some cays, there are, in addition, predators such as centipedes and spiders, that feed on these
terrestrial invertebrate scavengers. This assemblage
thus depends either directly or indirectly on energy and
256
CORAL CAYS, VEGETATIONAL SUCCESSION