Dataset: Coral clipping experiment - branching

Colonies of Antillogorgia elisabethae were clipped to simulate harvesting/disturbance at two sites in the Bahamas: a 4-meter depth on a reef east of Sandy Point on Great Abaco and a 12-meter depth site off San Salvador Island. At each site, colonies were clipped leaving a shortened primary branch and either 4 or 10 side branches. Both groups of clipped colonies were compared to adjacent colonies that were not clipped. "Control" colonies at Abaco had almost all been clipped for harvest 2-3 years prior to the experiment. There were no previous harvests at San Salvador. Colonies were photographed in June 1999 and June 2000. Photographs were taken at 640 X 480-bit resolution using a Sony Mavica digital camera (either MVC-7 or MVC-FD81) in an underwater housing. Growth of individual branches was determined by measuring digitized images. To obtain the images, colonies of A. elisabethae were carefully positioned between a 10 x 10-centimeter (cm) grid and a clear Plexiglas cover, which held the branches against the grid. The entire colony was photographed. Distortion created by taking the photographs at slight angles from perpendicular was corrected using Photoshop (Ver. 4.0, Adobe). In Photoshop, a 250 x 250-pixel grid was laid over the image and the image was adjusted using the program's distortion function until the 10-cm grid in the image matched the 250-pixel grid. Each branch was labeled with an identifying number and its length was measured using the program ImageJ. Branches were then re-identified in the images from June 2000 and new branches were identified. Per capita branching ratio was calculated by dividing the number of new branches by the number of old branches (branches that were present at the start of the experiment, in the first photo).