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CRAMP Rapid Assessment Transect Selection Process

To encompass as wide a spatial range as possible and to assess spatial variability, a “many but small” sampling strategy was adopted (McCune and Lesica 1992). The RAT is a trade-off between size and number of sampling units. This technique provides an efficient sampling design to assess extremely large areas as in this study. There are many advantages to selecting many, short transects over fewer transects of longer length (McCune and Grace 2001).

  • Cover of common species is more accurately and precisely estimated

  • Larger coverage of sites increases environmental representation

  • Smaller sampling units reduce bias against cryptic species by forcing visual contact to specific spots, avoiding selective species detection.

  • Reduces overestimation of rare species

  • Sampling effort and efficiency are not compromised

Transects within each site are randomly selected by generating 100 random points onto habitat maps using GPS Pathfinder Office 2.8. To assure adequate coverage of the different habitats and full representation of each site, a stratified design is employed. Points are stratified within depth ranges (<5 m, 5 to 10 m, and >10 m) and habitat types (coral, sand and macroalgae). Not all habitat types are present at every site. Navigational GPS is used in the field to determine the exact position of each point, marking the beginning of a transect. Link to “Geographic Coordinates” Where habitat maps are not available, a visual assessment of habitat type is conducted and depth is determined using either a depth gauge or fathometer. A random number of fin kicks is used to designate the beginning of each transect.

References:

McCune, B. and Grace, J. 2002. Analysis of Ecological Communities. MjM Software Design, Gleneden Beach, Oregon. USA.

McCune, B. and Lesica, P. 1992. The trade-off between species capture and quantitative accuracy in ecological inventory of lichens and bryophytes in forests in Montana. Bryologist 95:296-304.
 

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

808-236-7440 phone

808-236-7443 fax

email: jokiel@hawaii.edu