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Phase shift from a coral to a corallimorph-dominated reef associated with a shipwreck on Palmyra atoll.

Work TM, Aeby GS, Maragos JE - PLoS ONE (2008)

Bottom Line: We documented high densities of R. howesii near the ship that progressively decreased with distance from the ship whereas R. howesii were rare to absent in other parts of the atoll.This is the first time that a phase shift on a coral reef has been unambiguously associated with man-made structures.The extensive R. howesii invasion and subsequent loss of coral reef habitat at Palmyra also highlights the importance of rapid removal of shipwrecks on corals reefs to mitigate the potential of reef overgrowth by invasives.

View Article: PubMed Central - PubMed

Affiliation: U. S. Geological Survey-National Wildlife Health Center, Honolulu Field Station, Honolulu, Hawaii, United States of America. thierry_work@usgs.gov

ABSTRACT
Coral reefs can undergo relatively rapid changes in the dominant biota, a phenomenon referred to as phase shift. Various reasons have been proposed to explain this phenomenon including increased human disturbance, pollution, or changes in coral reef biota that serve a major ecological function such as depletion of grazers. However, pinpointing the actual factors potentially responsible can be problematic. Here we show a phase shift from coral to the corallimorpharian Rhodactis howesii associated with a long line vessel that wrecked in 1991 on an isolated atoll (Palmyra) in the central Pacific Ocean. We documented high densities of R. howesii near the ship that progressively decreased with distance from the ship whereas R. howesii were rare to absent in other parts of the atoll. We also confirmed high densities of R. howesii around several buoys recently installed on the atoll in 2001. This is the first time that a phase shift on a coral reef has been unambiguously associated with man-made structures. This association was made, in part, because of the remoteness of Palmyra and its recent history of minimal human habitation or impact. Phase shifts can have long-term negative ramification for coral reefs, and eradication of organisms responsible for phase shifts in marine ecosystems can be difficult, particularly if such organisms cover a large area. The extensive R. howesii invasion and subsequent loss of coral reef habitat at Palmyra also highlights the importance of rapid removal of shipwrecks on corals reefs to mitigate the potential of reef overgrowth by invasives.

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Details of corallimorph invasion near man-made objects.A) Extent of corallimorph infestation on western shelf of Palmyra Atoll NWR (close-up of Fig. 1C). Color codes correspond to estimated benthic cover of corallimorphs: red = high (>60%), yellow = medium (>30–60%), green = light (1–30%), blue = no visible corallimorphs. The ship is at the center of the red zone. Estimated percentage of coral cover at limits of corallimorph infestation. B) Box plot (5 and 95 percentile, median) of numbers of Rhodactis/m2 at 2 m intervals from 3 mooring buoys.
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pone-0002989-g002: Details of corallimorph invasion near man-made objects.A) Extent of corallimorph infestation on western shelf of Palmyra Atoll NWR (close-up of Fig. 1C). Color codes correspond to estimated benthic cover of corallimorphs: red = high (>60%), yellow = medium (>30–60%), green = light (1–30%), blue = no visible corallimorphs. The ship is at the center of the red zone. Estimated percentage of coral cover at limits of corallimorph infestation. B) Box plot (5 and 95 percentile, median) of numbers of Rhodactis/m2 at 2 m intervals from 3 mooring buoys.

Mentions: By the September 2007 survey, the invasion of the corallimorphs extended 2100 m at its widest point (Fig. 1C). Corallimorphs were present at distances from the ship ranging from 200 m to 1100 m (mean-590±300 m). The estimated coverage of the entire corallimorph-infested region was 1.0×106 m2 with the high, medium, and low density regions comprising 15% (0.14×106 m2), 26% (0.26×106 m2) and 59% (0.60×106 m2), respectively. Average density of corallimorph polyps within the high density area surrounding the wreck was 288 (SD±47) individuals per m2. Based on estimated area coverage of the infestation, estimated numbers of individual polyps surrounding the ship ranged from 52×106 to 141×106. Coral cover in areas at the periphery of the affected zone (populations of corals at risk of overgrowth) ranged from 6 to 64% with the highest (> = 25%) found in all but the southwest, northwest, and southeast sectors (Fig. 2A). Physical characteristics of the populations at risk ranged from mainly coral rubble to a diverse assemblage of stony coral species dominated by the genera Montipora, Pavona, and Pocillopora (Fig. 1E) Corallimorphs were also found surrounding three metal mooring buoys situated away from the impact of the wreck, and there was again a decrease in numbers of corallimorphs with increasing distance from buoys (Fig. 2B).


Phase shift from a coral to a corallimorph-dominated reef associated with a shipwreck on Palmyra atoll.

Work TM, Aeby GS, Maragos JE - PLoS ONE (2008)

Details of corallimorph invasion near man-made objects.A) Extent of corallimorph infestation on western shelf of Palmyra Atoll NWR (close-up of Fig. 1C). Color codes correspond to estimated benthic cover of corallimorphs: red = high (>60%), yellow = medium (>30–60%), green = light (1–30%), blue = no visible corallimorphs. The ship is at the center of the red zone. Estimated percentage of coral cover at limits of corallimorph infestation. B) Box plot (5 and 95 percentile, median) of numbers of Rhodactis/m2 at 2 m intervals from 3 mooring buoys.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2500175&req=5

pone-0002989-g002: Details of corallimorph invasion near man-made objects.A) Extent of corallimorph infestation on western shelf of Palmyra Atoll NWR (close-up of Fig. 1C). Color codes correspond to estimated benthic cover of corallimorphs: red = high (>60%), yellow = medium (>30–60%), green = light (1–30%), blue = no visible corallimorphs. The ship is at the center of the red zone. Estimated percentage of coral cover at limits of corallimorph infestation. B) Box plot (5 and 95 percentile, median) of numbers of Rhodactis/m2 at 2 m intervals from 3 mooring buoys.
Mentions: By the September 2007 survey, the invasion of the corallimorphs extended 2100 m at its widest point (Fig. 1C). Corallimorphs were present at distances from the ship ranging from 200 m to 1100 m (mean-590±300 m). The estimated coverage of the entire corallimorph-infested region was 1.0×106 m2 with the high, medium, and low density regions comprising 15% (0.14×106 m2), 26% (0.26×106 m2) and 59% (0.60×106 m2), respectively. Average density of corallimorph polyps within the high density area surrounding the wreck was 288 (SD±47) individuals per m2. Based on estimated area coverage of the infestation, estimated numbers of individual polyps surrounding the ship ranged from 52×106 to 141×106. Coral cover in areas at the periphery of the affected zone (populations of corals at risk of overgrowth) ranged from 6 to 64% with the highest (> = 25%) found in all but the southwest, northwest, and southeast sectors (Fig. 2A). Physical characteristics of the populations at risk ranged from mainly coral rubble to a diverse assemblage of stony coral species dominated by the genera Montipora, Pavona, and Pocillopora (Fig. 1E) Corallimorphs were also found surrounding three metal mooring buoys situated away from the impact of the wreck, and there was again a decrease in numbers of corallimorphs with increasing distance from buoys (Fig. 2B).

Bottom Line: We documented high densities of R. howesii near the ship that progressively decreased with distance from the ship whereas R. howesii were rare to absent in other parts of the atoll.This is the first time that a phase shift on a coral reef has been unambiguously associated with man-made structures.The extensive R. howesii invasion and subsequent loss of coral reef habitat at Palmyra also highlights the importance of rapid removal of shipwrecks on corals reefs to mitigate the potential of reef overgrowth by invasives.

View Article: PubMed Central - PubMed

Affiliation: U. S. Geological Survey-National Wildlife Health Center, Honolulu Field Station, Honolulu, Hawaii, United States of America. thierry_work@usgs.gov

ABSTRACT
Coral reefs can undergo relatively rapid changes in the dominant biota, a phenomenon referred to as phase shift. Various reasons have been proposed to explain this phenomenon including increased human disturbance, pollution, or changes in coral reef biota that serve a major ecological function such as depletion of grazers. However, pinpointing the actual factors potentially responsible can be problematic. Here we show a phase shift from coral to the corallimorpharian Rhodactis howesii associated with a long line vessel that wrecked in 1991 on an isolated atoll (Palmyra) in the central Pacific Ocean. We documented high densities of R. howesii near the ship that progressively decreased with distance from the ship whereas R. howesii were rare to absent in other parts of the atoll. We also confirmed high densities of R. howesii around several buoys recently installed on the atoll in 2001. This is the first time that a phase shift on a coral reef has been unambiguously associated with man-made structures. This association was made, in part, because of the remoteness of Palmyra and its recent history of minimal human habitation or impact. Phase shifts can have long-term negative ramification for coral reefs, and eradication of organisms responsible for phase shifts in marine ecosystems can be difficult, particularly if such organisms cover a large area. The extensive R. howesii invasion and subsequent loss of coral reef habitat at Palmyra also highlights the importance of rapid removal of shipwrecks on corals reefs to mitigate the potential of reef overgrowth by invasives.

Show MeSH
Related in: MedlinePlus