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Episodic Disturbance from Boat Anchoring Is a Major Contributor to, but Does Not Alter the Trajectory of, Long-Term Coral Reef Decline.

Forrester GE, Flynn RL, Forrester LM, Jarecki LL - PLoS ONE (2015)

Bottom Line: Isolating the relative effects of episodic disturbances and chronic stressors on long-term community change is challenging.We assessed the impact of an episodic disturbance associated with human visitation (boat anchoring) relative to other drivers of long-term change on coral reefs.This apparent lack of synergism between the effect of this episodic human impact and other chronic stressors is consistent with the few other long-term studies of episodic impacts, and suggests that action to mitigate anchor damage should yield predictable benefits.

View Article: PubMed Central - PubMed

Affiliation: Department of Natural Resources Science, University of Rhode Island, 1 Greenhouse Road, Kingston, Rhode Island, 02881, United States of America.

ABSTRACT
Isolating the relative effects of episodic disturbances and chronic stressors on long-term community change is challenging. We assessed the impact of an episodic disturbance associated with human visitation (boat anchoring) relative to other drivers of long-term change on coral reefs. A one-time anchoring event at Crab Cove, British Virgin Islands, in 2004 caused rapid losses of coral and reef structural complexity that were equal to the cumulative decline over 23 years observed at an adjacent site. The abundance of small site-attached reef fishes dropped by approximately one quarter after the anchoring event, but this drop was not immediate and only fully apparent two years after the anchoring event. There was no obvious recovery from the impact, and no evidence that this episodic impact accelerated or retarded subsequent declines from other causes. This apparent lack of synergism between the effect of this episodic human impact and other chronic stressors is consistent with the few other long-term studies of episodic impacts, and suggests that action to mitigate anchor damage should yield predictable benefits.

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Related in: MedlinePlus

Mean absolute coral cover (%) over time at Crab Cove, showing changes inside and outside the area damaged by the 2004 anchoring event.The dotted vertical line indicates the timing of the 2004 anchoring event.
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pone.0144498.g003: Mean absolute coral cover (%) over time at Crab Cove, showing changes inside and outside the area damaged by the 2004 anchoring event.The dotted vertical line indicates the timing of the 2004 anchoring event.

Mentions: Within the area damaged by the Holo-Kai, there was an abrupt loss of coral that occurred directly after the anchoring event, which did not occur outside of the area affected by the Holo-Kai (Fig 3). In both parts of the site, there was also a gradual decline in coral cover from 1992-present (Fig 3). A significant impact of the anchoring event was supported by the results of both the BACI analysis and the linear mixed model. Support from the linear mixed model was provided by a significant interaction between the “control versus impact” and “before versus after” effects (F1,64 = 63.4, p = 0.012). The t-test supported an anchoring impact because the control-impact differences were greater after the anchoring event than before (t14 = 5.98, p = 0.0004).


Episodic Disturbance from Boat Anchoring Is a Major Contributor to, but Does Not Alter the Trajectory of, Long-Term Coral Reef Decline.

Forrester GE, Flynn RL, Forrester LM, Jarecki LL - PLoS ONE (2015)

Mean absolute coral cover (%) over time at Crab Cove, showing changes inside and outside the area damaged by the 2004 anchoring event.The dotted vertical line indicates the timing of the 2004 anchoring event.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4696730&req=5

pone.0144498.g003: Mean absolute coral cover (%) over time at Crab Cove, showing changes inside and outside the area damaged by the 2004 anchoring event.The dotted vertical line indicates the timing of the 2004 anchoring event.
Mentions: Within the area damaged by the Holo-Kai, there was an abrupt loss of coral that occurred directly after the anchoring event, which did not occur outside of the area affected by the Holo-Kai (Fig 3). In both parts of the site, there was also a gradual decline in coral cover from 1992-present (Fig 3). A significant impact of the anchoring event was supported by the results of both the BACI analysis and the linear mixed model. Support from the linear mixed model was provided by a significant interaction between the “control versus impact” and “before versus after” effects (F1,64 = 63.4, p = 0.012). The t-test supported an anchoring impact because the control-impact differences were greater after the anchoring event than before (t14 = 5.98, p = 0.0004).

Bottom Line: Isolating the relative effects of episodic disturbances and chronic stressors on long-term community change is challenging.We assessed the impact of an episodic disturbance associated with human visitation (boat anchoring) relative to other drivers of long-term change on coral reefs.This apparent lack of synergism between the effect of this episodic human impact and other chronic stressors is consistent with the few other long-term studies of episodic impacts, and suggests that action to mitigate anchor damage should yield predictable benefits.

View Article: PubMed Central - PubMed

Affiliation: Department of Natural Resources Science, University of Rhode Island, 1 Greenhouse Road, Kingston, Rhode Island, 02881, United States of America.

ABSTRACT
Isolating the relative effects of episodic disturbances and chronic stressors on long-term community change is challenging. We assessed the impact of an episodic disturbance associated with human visitation (boat anchoring) relative to other drivers of long-term change on coral reefs. A one-time anchoring event at Crab Cove, British Virgin Islands, in 2004 caused rapid losses of coral and reef structural complexity that were equal to the cumulative decline over 23 years observed at an adjacent site. The abundance of small site-attached reef fishes dropped by approximately one quarter after the anchoring event, but this drop was not immediate and only fully apparent two years after the anchoring event. There was no obvious recovery from the impact, and no evidence that this episodic impact accelerated or retarded subsequent declines from other causes. This apparent lack of synergism between the effect of this episodic human impact and other chronic stressors is consistent with the few other long-term studies of episodic impacts, and suggests that action to mitigate anchor damage should yield predictable benefits.

Show MeSH
Related in: MedlinePlus