Flynn RL and Forrester GE (2019), Boat anchoring contributes substantially to cor...

ECB-ART-47258

PeerJ 2019 Jan 01;7:e7010. doi: 10.7717/peerj.7010.

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Boat anchoring contributes substantially to coral reef degradation in the British Virgin Islands.

Flynn RL , Forrester GE .

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Community decline is often linked to anthropogenic activities. Coral reef declines, for example, have been linked to overfishing and climate change, but impacts of coastal development, pollution, and tourism have received increasing attention. Here, we isolated the impact of one little-studied aspect of recreational activity on coral reefs-damage from boat anchoring-by performing a survey of 24 sites in the British Virgin Islands (BVI) subject to varying levels of anchoring activity. The percent cover of hard corals and sea fans was reduced by a factor of ∼1.7 and ∼2.6 respectively at highly anchored sites. Hard coral colonies were 40% smaller in surface area and ∼60% less dense at sites experiencing high anchoring frequency. In addition, highly anchored sites supported only ∼60% of the species richness of little anchored sites. Frequently anchored sites were ∼60% as structurally complex and supported less than half as many fish as those rarely anchored, with 5 of 7 fish functional groups affected. Roughly 24% of BVI coral reef by area appears suitable for anchoring, suggesting that impacts associated with boat anchoring may be both locally severe and more pervasive than previously appreciated.

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Genes referenced: impact LOC100887844

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	Figure 1. Locations of reefs surveyed in the British Virgin Islands.Sites are coded to indicate whether they categorized as experiencing high, medium, or low frequency of anchoring. Sites were selected in 10 groups (numbered and circled) that were close in proximity.
	Figure 2. Anchoring activity observed using satellite imagery.Sites were classified as high, medium or low anchoring based on expert opinion. This classification was checked by counting anchored boats at each site. Plotted are means (±SE) and letters above bars indicate significant differences based on a multiple comparison test (means that do not differ share a letter). Map Data from GoogleEarth and DigitalGlobe.
	Figure 3. Hard coral and sea fan cover differ across a gradient of anchoring activity.Means (±SE) of proportional bottom cover for scleractinian corals (A) and sea fans (B). For each taxon, letters above bars indicate significant differences based on a multiple comparison test (means that do not differ share a letter).
	Figure 4. Coral diversity, abundance and size differ across a gradient of anchoring activity.Plotted are means (±SE) of (A) Coral colony surface area, (B) coral colony density, (C) coral species richness and (D) coral abundance. Letters above bars indicate significant differences based on a multiple comparison test (means that do not differ share a letter).
	Figure 5. Rugosity differs across a gradient of anchoring activity.Plotted are means (±SE) of reef rugosity and letters above bars indicate significant differences based on a multiple comparison test (means that do not differ share a letter).
	Figure 6. Fish abundance and diversity differ across a gradient of anchoring activity.Plotted are means (±SE) of fish density (left) and species richness (right). Letters above bars indicate significant differences based on a multiple comparison test (means that do not differ share a letter).

References [+] :

Alvarez-Filip, Flattening of Caribbean coral reefs: region-wide declines in architectural complexity. 2009, Pubmed, Echinobase