CRAMP Rapid Assessment. Benthic Protocols
A photographic transecting method was selected for use in this research for several reasons. Method selection criteria required data compatibility with CRAMP sites incorporated into this study. A quantitative method is critical to most advanced statistical procedures. The photographic method is not restrained by the limitations of many other benthic sampling methods. Precision using this photographic technique was determined to be high (~95% similarity among observers) compared to insitu observations (Brown et al. 2004). Although initial costs are high, cost effectiveness surpasses visual techniques after only ten surveys (Brown et al. 2004). While post processing time increases, costly underwater dive time is greatly reduced with the use of photographic techniques. Photographic methods allow for archiving and data verification, which is critical in addressing further questions, and in quality control. The disadvantage of limited resolution has been resolved with recent technological advances.
CRAMP began using video techniques in 1999 and has since replaced this with digital stills in 2002. Prior to the switch, the compatibility of the methods was assessed through intercalibration, using both methods at a large number of sites (30) that encompassed a wide range of coral cover.
Technological advances currently provide higher resolution with still digital cameras than with video cameras. The valuable insitu time is shorter as well as the time spent processing the images and frame-grabbing is completely eliminated. The video camera cannot keep an exact distance from the bottom while the still camera mounted on a simple monopod assures a constant distance. With a still camera, there are no oblique angles that can affect results since the camera is held vertical by the monopod. It is however important to use consistent methodology when comparing sites over time. It is possible though to switch methodologies midstream and is in fact preferable in long-term programs if the new methodology is superior.
To assess the characteristics of benthic populations, high-resolution digital images are taken along a 10 m transect using an Olympus 5050 zoom digital camera with an Olympus PT050 underwater housing. The camera is mounted to an aluminum monopod frame, 1.7 m from the substrate to provide a 50x69 cm image. A 6 cm bar provides a measurement scale. The software program PhotoGrid (Bird 2001) is used to quantify percent cover, richness and diversity of corals, algal functional groups and substrate cover.
Images are downloaded and the 20 images from each 10 m transect are imported into PhotoGrid where 50 randomly selected points are projected onto each image. CRAMP has recently reduced the number of images to 10 to assure no overlapping sections. These data are saved in a comma separated values (CSV) file, proofread in Excel and imported into Microsoft Access XP, a relational database. Access data is queried and exported to statistical programs for analyses.
Last Update: 04/21/2008
By: Lea Hollingsworth
Hawai‘i Coral Reef Assessment & Monitoring Program
Hawai‘i Institute of Marine Biology
P.O. Box 1346
Kāne‘ohe, HI 96744