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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
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