Transect Work

One of the major components of the PCRF archive of reefs around the planet comprises a video/photo library of footage taken along carefully laid transect lines. Upon each reef studied intensively, transect lines are laid and filmed or photographed. The footage is then stored at the PCRF archive in Los Angeles, and copies sent to the College of Charleston for further analysis.

Mark lays the chain for the video transect work,
Kavieng, Papua New Guinea

 Methodology - since June, 2004

            At least three digital still image transects are conducted in each zone of every study site (ie. shallow and deep or inside and outside of an atoll lagoon).  Divers descend with two weighted buoys labeled A and B, measuring tape, a digital still camera, underwater writing slates, and pencils.  Transects locations are chosen based on sites that are representative of the entire reef ecosystem.  A 20 meter line is laid between 5-10 meters deep along the bottom contour with the buoys at both ends.  A bearing is taken from buoy A to buoy B and the boat tender takes GPS coordinates at both buoys.  Two lines of digital still images are taken two meters on either side of the central line.  Each line consists of 30-50 digital still images, which are taken 40-50 cm above the reef.  A total of approximately 600 images are taken within the entire study site.  Coral identification to genus level, and species level when possible, is done within the 80 m² zone, running 2 meters either side of the center line. Fish identification, including a species and population count is done in the area surrounding each transect to a maximum depth of 15 meters.  Both coral and fish identification are done for 45 minutes during each transect dive.  Secchi disk readings for visibility, cloud cover and sea state are also recorded for each transect dive.

Transect images are analyzed using PointCount 99, developed by Phil Dustan at the College of Charleston.  PointCount 99 generates 10 random points on each transect image.  Each of these points is then labeled live coral, dead coral, other, which includes rubble, rock, sand, and soft coral, and unidentifiable data point.  The data is then imported into a spreadsheet and can be analyzed to obtain the percent cover of each of the categories listed above.   

 Click here for methodology prior to June, 2004