AVIS-IBIS

Birds of Indian Subcontinent

The Role of a Hurricane in the Expansion of Disturbances Initiated by Motor Vessels on Seagrass Banks

Publication Type:Journal Article
Year of Publication:2002
Authors:Whitfield, PE, W. Kenworthy, J, Hammerstrom, KK, Fonseca, MS
Journal:Journal of Coastal Research
Date Published:2002
ISBN Number:07490208
Keywords:Calidris, Calidris canutus, Scolopacidae
Abstract:While investigating the ecology of physically disturbed seagrass and Porites porites coral banks in the Florida Keys National Marine Sanctuary (FKNMS), we documented the effect of Hurricane Georges on the recovery of injuries created by large motor vessels. Near the intersection of two main routes for vessel traffic in the Red Bay Bank region of the FKNMS, we found that blowholes caused by vessel groundings (n = 146), as opposed to propeller scars (n = 50), accounted for a majority of the vessel-related injuries on shallow seagrass banks. Evidence from four large motor vessel grounding sites that were mapped before and after a category 2 hurricane (Georges) with wind speeds of 96 knots (176 kmph) indicated an increase in injury size associated with the storm. At a site where a tugboat grounding had destroyed 100% of the macrophytes growing on 7,363 m² of a shallow bank, recovery was interrupted and reversed by Hurricane Georges. In January 1998, 4.5 yr after the original injury, macroalgae had recovered to 85% and seagrasses to 11% of the original 100% cover at the grounding site. In the second survey two months after Hurricane Georges, seagrasses had declined to ≤ 1% and macroalgae to 23% of the original cover. Twenty-one months later, seagrasses and macroalgae had recovered to near pre-hurricane levels, but cover was still much less than the original cover. Following the hurricane, the injured area increased from 1,576 m² to 2,514 m², a 63% increase. Three other large vessel-grounding sites exhibited at least a 65% increase in the size of their blowholes following Hurricane Georges. Our data and observations suggest that large blowholes created by vessel injuries are unstable and will continue to be vulnerable to storm events many years after the original disturbance. Depending on a bank's location, orientation, and its proximity to the reef environment, consideration should be given to a range of pro-active and post-injury responses including, but not restricted to: (1) physically regrading large blowholes to increase the physical stability of the site; and (2) strategic placement of navigational aids to direct vessel traffic away from shallow banks.
URL:http://www.jstor.org/stable/25736345
Short Title:Journal of Coastal Research
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith