rugosity index for habitat complexity
eakin at ogp.noaa.gov
Wed May 27 11:16:49 EDT 1998
Reply to: RE>rugosity index for habitat complexity
One measurement is the one that I have used in Panama. It was published in:
Eakin, C.M. Where have all the carbonates gone? A model comparison of calcium carbonate
budgets before and after the 1982-1983 El Nino. Coral Reefs 15(2): 109-119.
The description follows:
Three dimensional structure (i.e. topographic complexity) was determined by draping a brass chain along the bottom under lines bisecting the center of the quadrat on one of the surveys. The length of chain required to trace the surface under 1 m was recorded for both the east-west (x) and north-south (y) bisecting lines. This was used in adjusting the CaCO3 deposition by coralline algae
Unlike the growth form of Pocillopora sp., which is three-dimensionally complex and imparts topographic complexity to the reef, crustose coralline algae form thin crusts that match the fine contours of the underlying substrata. Thus, the area occupied by coralline algae (three dimensional surface area) often is greater than their planar projection, requiring that the deposition rate per unit area measured on a smooth surface (1.9 kg/m2/y, Eakin 1992) be adjusted to quantify growth on natural substrata. Thus, the deposition by coralline algae on a smooth surface was multiplied by an areal adjustment based on topographic complexity:
Areal Adjustment = 4/(1/x+1/y)2
where x and y are the two chain lengths (above) in meters. Actual adjustments for individual quadrats ranged from near 1.0 (flat) to 4.0.
A slightly different formulation was described in my dissertation:
Eakin, C.M. 1991 The damselfish-algal lawn symbiosis and its influence on the bioerosion of an
El Nino impacted coral reef, Uva Island, Pacific Panama. Ph.D. dissertation, Univ. of Miami,
That description follows:
As variations in the complexity of substrata can be important in providing shelter, topographic complexity was determined as follows. At the first 10 quadrats of the random walk surveys, a rigid 1 m2 quadrat, bisected in the x and y directions by rigid crossbars, was placed level with the uppermost surface of the substratum. A brass chain was then draped along the bottom under one of the 1 m bisecting bars, so that it matched the rise and fall of the substratum. The length of chain required to trace the surface under 1 m was recorded, and repeated for the second crossbar. A single measure of topographic complexity was calculated for each quadrat as:
topographic complexity = 1 - (1/x + 1/y)/2
where x and y are the two chain lengths in meters. This yields values ranging from zero to asymptotically approaching unity. As no surfaces in the field were perfectly flat and there were limits to the complexity of surfaces, the values ranged from near zero to 0.5, the latter indicating surfaces producing chain lengths twice that of their planar projections.
C. Mark Eakin, Ph.D.
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Internet: eakin at ogp.noaa.gov
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