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Self-generated morphology in lagoon reefs.

Blakeway D, Hamblin MG - PeerJ (2015)

Bottom Line: In these situations reef morphology can be considered a phenotype of the predominant reef building organism.The capacity to infer coral type from reef morphology can potentially be used to identify and map specific coral habitat in remotely sensed images.More generally, identifying ecological mechanisms underlying other examples of self-generated reef morphology can potentially improve our understanding of present-day reef ecology, because any ecological process capable of shaping a reef will almost invariably be an important process in real time on the living reef.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Earth and Environment, University of Western Australia , Crawley , Western Australia, Australia.

ABSTRACT
The three-dimensional form of a coral reef develops through interactions and feedbacks between its constituent organisms and their environment. Reef morphology therefore contains a potential wealth of ecological information, accessible if the relationships between morphology and ecology can be decoded. Traditionally, reef morphology has been attributed to external controls such as substrate topography or hydrodynamic influences. Little is known about inherent reef morphology in the absence of external control. Here we use reef growth simulations, based on observations in the cellular reefs of Western Australia's Houtman Abrolhos Islands, to show that reef morphology is fundamentally determined by the mechanical behaviour of the reef-building organisms themselves-specifically their tendency to either remain in place or to collapse. Reef-building organisms that tend to remain in place, such as massive and encrusting corals or coralline algae, produce nodular reefs, whereas those that tend to collapse, such as branching Acropora, produce cellular reefs. The purest reef growth forms arise in sheltered lagoons dominated by a single type of reef builder, as in the branching Acropora-dominated lagoons of the Abrolhos. In these situations reef morphology can be considered a phenotype of the predominant reef building organism. The capacity to infer coral type from reef morphology can potentially be used to identify and map specific coral habitat in remotely sensed images. More generally, identifying ecological mechanisms underlying other examples of self-generated reef morphology can potentially improve our understanding of present-day reef ecology, because any ecological process capable of shaping a reef will almost invariably be an important process in real time on the living reef.

No MeSH data available.


Related in: MedlinePlus

Reefs generated by the basic model.(A) Two-dimensional plan view of a patch reef after 80 iterations (8,000 years) of growth from a single seed coral. Shading corresponds to depth—the reef top at sea level is white and the surrounding seafloor at 30 m depth is black. This patch reef reached sea level in approximately 45 iterations (4,500 years), and by 80 iterations has developed a 15 m wide reef flat. (B) Three-dimensional oblique view of the patch reef in (A), showing the irregular surface morphology caused by projecting corals. The reef slopes are approximately 65°. (C) Two-dimensional plan view of a coalescing patch reef system after 80 iterations. Only the uppermost 10 m of the reef system is shown, simulating an aerial view with 10 m water visibility. (D) Three-dimensional oblique view of the reefs in C.
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fig-8: Reefs generated by the basic model.(A) Two-dimensional plan view of a patch reef after 80 iterations (8,000 years) of growth from a single seed coral. Shading corresponds to depth—the reef top at sea level is white and the surrounding seafloor at 30 m depth is black. This patch reef reached sea level in approximately 45 iterations (4,500 years), and by 80 iterations has developed a 15 m wide reef flat. (B) Three-dimensional oblique view of the patch reef in (A), showing the irregular surface morphology caused by projecting corals. The reef slopes are approximately 65°. (C) Two-dimensional plan view of a coalescing patch reef system after 80 iterations. Only the uppermost 10 m of the reef system is shown, simulating an aerial view with 10 m water visibility. (D) Three-dimensional oblique view of the reefs in C.

Mentions: Representation of branching Acropora was guided by the output of the basic model (Fig. 8). The basic model reefs have an irregular ‘spiky’ surface, with corals projecting up to four metres above the surrounding reef. Such projections cannot occur on real branching Acropora reefs because, due to their ‘brittle tree’ morphology, any branching Acropora colonies that grow more than a metre or two above their surroundings will inevitably collapse (Maragos, 1972; Bak, 1976; see Fig. 5B). This is not necessarily a disadvantage. Because broken fragments can survive and grow to form new colonies, collapse and fragmentation are recognised as inherent and significant modes of reproduction and short range dispersal in branching Acropora (Gilmore & Hall, 1976; Tunnicliffe, 1981; Bothwell, 1982; Highsmith, 1982). Collapse is represented in the branching Acropora model by imposing a maximum height differential between neighbours (hereafter termed collapse limit) of two metres, such that corals growing to project two metres above any neighbouring cell are prevented from growing upward until the deeper cell grows. Although they cannot grow upward, projecting corals contribute to the growth probability of neighbouring cells in two ways: first, they ‘support’ neighbouring corals, ensuring they are unrestricted by the collapse limit; and second, they may ‘collapse into’ deeper neighbouring cells (i.e., they increase the neighbour probability of those cells). Although this representation of collapse involves no subtraction of height from the projecting colony, it remains valid because it is equivalent to the projecting colony growing a metre then collapsing back a metre during the iteration. Because the imposition of the collapse limit slows reef growth, the time represented by each iteration is reduced to 40 years. This gives a mean vertical reef accretion rate of 9 mm/yr, approximating that of the Abrolhos cellular reefs (Eisenhauer et al., 1993; Collins et al., 1993).


Self-generated morphology in lagoon reefs.

Blakeway D, Hamblin MG - PeerJ (2015)

Reefs generated by the basic model.(A) Two-dimensional plan view of a patch reef after 80 iterations (8,000 years) of growth from a single seed coral. Shading corresponds to depth—the reef top at sea level is white and the surrounding seafloor at 30 m depth is black. This patch reef reached sea level in approximately 45 iterations (4,500 years), and by 80 iterations has developed a 15 m wide reef flat. (B) Three-dimensional oblique view of the patch reef in (A), showing the irregular surface morphology caused by projecting corals. The reef slopes are approximately 65°. (C) Two-dimensional plan view of a coalescing patch reef system after 80 iterations. Only the uppermost 10 m of the reef system is shown, simulating an aerial view with 10 m water visibility. (D) Three-dimensional oblique view of the reefs in C.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4499466&req=5

fig-8: Reefs generated by the basic model.(A) Two-dimensional plan view of a patch reef after 80 iterations (8,000 years) of growth from a single seed coral. Shading corresponds to depth—the reef top at sea level is white and the surrounding seafloor at 30 m depth is black. This patch reef reached sea level in approximately 45 iterations (4,500 years), and by 80 iterations has developed a 15 m wide reef flat. (B) Three-dimensional oblique view of the patch reef in (A), showing the irregular surface morphology caused by projecting corals. The reef slopes are approximately 65°. (C) Two-dimensional plan view of a coalescing patch reef system after 80 iterations. Only the uppermost 10 m of the reef system is shown, simulating an aerial view with 10 m water visibility. (D) Three-dimensional oblique view of the reefs in C.
Mentions: Representation of branching Acropora was guided by the output of the basic model (Fig. 8). The basic model reefs have an irregular ‘spiky’ surface, with corals projecting up to four metres above the surrounding reef. Such projections cannot occur on real branching Acropora reefs because, due to their ‘brittle tree’ morphology, any branching Acropora colonies that grow more than a metre or two above their surroundings will inevitably collapse (Maragos, 1972; Bak, 1976; see Fig. 5B). This is not necessarily a disadvantage. Because broken fragments can survive and grow to form new colonies, collapse and fragmentation are recognised as inherent and significant modes of reproduction and short range dispersal in branching Acropora (Gilmore & Hall, 1976; Tunnicliffe, 1981; Bothwell, 1982; Highsmith, 1982). Collapse is represented in the branching Acropora model by imposing a maximum height differential between neighbours (hereafter termed collapse limit) of two metres, such that corals growing to project two metres above any neighbouring cell are prevented from growing upward until the deeper cell grows. Although they cannot grow upward, projecting corals contribute to the growth probability of neighbouring cells in two ways: first, they ‘support’ neighbouring corals, ensuring they are unrestricted by the collapse limit; and second, they may ‘collapse into’ deeper neighbouring cells (i.e., they increase the neighbour probability of those cells). Although this representation of collapse involves no subtraction of height from the projecting colony, it remains valid because it is equivalent to the projecting colony growing a metre then collapsing back a metre during the iteration. Because the imposition of the collapse limit slows reef growth, the time represented by each iteration is reduced to 40 years. This gives a mean vertical reef accretion rate of 9 mm/yr, approximating that of the Abrolhos cellular reefs (Eisenhauer et al., 1993; Collins et al., 1993).

Bottom Line: In these situations reef morphology can be considered a phenotype of the predominant reef building organism.The capacity to infer coral type from reef morphology can potentially be used to identify and map specific coral habitat in remotely sensed images.More generally, identifying ecological mechanisms underlying other examples of self-generated reef morphology can potentially improve our understanding of present-day reef ecology, because any ecological process capable of shaping a reef will almost invariably be an important process in real time on the living reef.

View Article: PubMed Central - HTML - PubMed

Affiliation: School of Earth and Environment, University of Western Australia , Crawley , Western Australia, Australia.

ABSTRACT
The three-dimensional form of a coral reef develops through interactions and feedbacks between its constituent organisms and their environment. Reef morphology therefore contains a potential wealth of ecological information, accessible if the relationships between morphology and ecology can be decoded. Traditionally, reef morphology has been attributed to external controls such as substrate topography or hydrodynamic influences. Little is known about inherent reef morphology in the absence of external control. Here we use reef growth simulations, based on observations in the cellular reefs of Western Australia's Houtman Abrolhos Islands, to show that reef morphology is fundamentally determined by the mechanical behaviour of the reef-building organisms themselves-specifically their tendency to either remain in place or to collapse. Reef-building organisms that tend to remain in place, such as massive and encrusting corals or coralline algae, produce nodular reefs, whereas those that tend to collapse, such as branching Acropora, produce cellular reefs. The purest reef growth forms arise in sheltered lagoons dominated by a single type of reef builder, as in the branching Acropora-dominated lagoons of the Abrolhos. In these situations reef morphology can be considered a phenotype of the predominant reef building organism. The capacity to infer coral type from reef morphology can potentially be used to identify and map specific coral habitat in remotely sensed images. More generally, identifying ecological mechanisms underlying other examples of self-generated reef morphology can potentially improve our understanding of present-day reef ecology, because any ecological process capable of shaping a reef will almost invariably be an important process in real time on the living reef.

No MeSH data available.


Related in: MedlinePlus