Methodology - Prior to June, 2004

Sites for filming are selected around the reef that will give a fair representation of the bottom cover, species diversity and state of health of the reef. Unless it is truly representative of the diversity of hard coral species found on the reef, monospecific patches are avoided for video work. When the sites have been earmarked as suitable for filming, a team of five or six divers prepare themselves for filming an underwater transect.

First, two metal pins must be secured in the substrate - dead coral or rock. These pins are used to secure two lengths of PVC pipe which will mark the start and finish lines for the transect. The distance between the PVC pipes is measured to 22 meters. Three strings are then tied from one PVC pipe to the other and parallel to each other. These strings are about a meter apart. They act as a guide for the next step, which is to unravel a roll of light chain from one pipe to the other. The chain is dropped gently onto the corals beneath, brushing gently against the strings to keep a straight line. The strings become especially crucial in helping to lay the chains straight if there is surge or current. Once the chains are safely laid, the strings are removed and the transect lines are ready to be filmed.

The videographer then passes over the transect lines, at a steady speed and keeping a constant distance between the camera lens and the contour of the reef beneath. Each line is 'slated' for subsequent identification.

Details from transect results showing healthy table Acropora colony on left and dead colony overgrown by macroalgae on right While the videographer is at work, the mapping team take a series of readings to enable finding the sites of the transect pins in the future. GPS coordinates are taken from the water's surface directly above each of the two pins together with compass readings towards three visible landmarks eg. tip of an island, distinctive building on land etc. And underwater, a diver maps the topography surrounding the location of the transect pins.

When all tasks have been completed, the chains are carefully wound back onto their spools, the PVC and steel pins removed and all equipment returned to the research vessel.

Sean draws a map of the transect area (left)
Eddie secures the PVC pipe (right)

Each frame of underwater video can be analyzed using specific computer programming to give statistical information about the composition and state of health of the reef. Since 1995, almost 30 hours of underwater transect video has been gathered, amassing nearly 3 million frames of video documentation.