Access the data
The access to the photo-quadrats is through the Studied sites.

The main goal for this technique is to estimate the coral cover (quantitative variable) classified by genus (qualitative variable). This technique is applied at exactly the same place every time, allowing a time lapse of the exact same portion of the reef.

The method

The method consists in taking pictures of a rectangular portion of the reef 20 m long and 1 m wide (20 m²). To do so, a steel cable is tensed with high tension between 2 stakes with a turnbuckle, on the outer slope (between 7 and 13 meters). On that cable, a series of cable ties is attached at regular intervals. These cable ties provide support for positioning an aluminium frame (1 m x 1 m = external dimensions) along the cable over 20 successive positions.


Sample Images
Sample Images

At each position, a picture of the frame is taken, hence producing a full representation of the 20 m² reef band.
Quadrat2
When the field work is done, only the two stakes and soft short ropes are left on site. The stakes being permanently left on site allow pictures taken year after year to show the evolution of the coral cover as a time lapse.

Data processing

The technique used is a Point Intercept estimates. Eighty one points are position over the picture of the frame. These 81 points are systematically positioned along spaced lines. The identification and counting of live coral under each point give an estimate of the coral cover (= 100 x number of points with live coral / 81). The partial cover for each genus is given by identifying the genus for each point.

For a station of 20 quadrats, a total of 1620 points is analysed.
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