[Coral-List] Best practice for LIT surveys
wera.leujak at web.de
Sun Jan 4 12:41:11 EST 2009
we have tested six commonly used coral survey methods (line intercept transect, line point transect, mapping of quadrats, photoquadrats analysed in 2 different ways and video belt transects) on a Red Sea reef and found LIT to perform poorly in terms of precision and accuracy (Leujak & Ormond 2007, Journal of Experimental Marine Biology and Ecology 351, pp 168-187).
LIT overestimated hard and soft coral cover by 3 to 6% (live coral cover was 34%, predominantly large colonies) and we believe that this is due to what we termed the contour effect. Although our transect line was stretched taught and attached every 5m along the transect the tape still tended to follow the contours of larger colonies, thereby estimating the circumferential area of the coral rather than the smaller planar area (as is the case for quadrats that served as our baseline). Also, using LIT in the field was extremely time consuming (10m recorded during 1 dive of approx. 60min) and we had difficulties determining what substrate lay beneath the transect line, even when using a plumb line. We were often tempted to record a coral which might be directly below the line in case an error is made by omitting to record it.
Power analysis indicated that the sample size required to yield an 80% chance of detecting even a 20% relative difference in total hard coral cover was 135m for LIT, with much greater sample sizes required to detect similar differences in the cover of individual coral growth forms. The poor repeatability of LIT was responsible for these high sampling sizes. We therefore did not recommend the use of LIT in a monitoring programme for Red Sea reefs but suggested photoquadrats instead.
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