3. Methodology for Preparation of Figures 9 to 12 and Appendix C 

 Figures C-3 to C-6 (Boundaries of Major Associations) . 



ARCO Drawing No. CE-1-8, dated 3 March 1965, was used as a base 

 chart for plotting field-acquired data on boundaries of species asso- 

 ciations. Different tide levels were shown on the drawing for four 

 different parts of the island; these levels corresponded to times 

 when measurements were taken over the four parts of the island. Spot 

 measurements taken between fixed reference points and the waterline 

 (which was not at MLLW) at times of corresponding tidal heights 

 agreed well with the distances represented on the drawing. 



The first step was to adjust the waterline to MLLW. This was 

 done by dividing the tidal height (e.g., +1.2 meters MLLW) by the 

 tangent of the side-slope angle. The slope angle for each side was 

 determined by averaging data obtained during the talus bed measure- 

 ment phase of this project (see Figs. 5 to 8) . The resulting MLLVJ 

 line is as it would appear if observed directly from some altitude 

 above the island. True distances measured down the slope of each 

 side may be determined using the scale provided on each island sector 

 chart (Fig-5. 9 to 12 and Figs. C-3 to C-6). 



Next, distances measured from fixed reference points at the top 

 edge of the island to the upper limit of the splash zone (barnacle- 

 limpet association) were trigonometrically corrected for slope and 

 plotted. The width of the zone bounded at the top by the barnacle- 

 limpet line and at the bottom by the MLLW line (representing the main 

 part of the intertidal zone) was uniform around the island, providing 

 a positive check on accuracy of the waterline shown on the drawing. 

 Only 2 of the 15 points showed discrepancies. One on the south side 

 was off by about 1.2 meters, and the decision was made to redraw the 

 MLLW line at this point to maintain width uniformity for the inter- 

 tidal. The other, on the west side, was off by almost 6.1 meters 

 (the measurement during this study indicated a shorter distance) . 

 This discrepancy may be due to movements of tetrapods in response to 

 wave forces since the 1965 drawing (a seraisubmerged tetrapod lies 

 just seaward of the "first" waterline); or the difference may be a 

 result of the manner in which the measuring tape was laid over the 

 tetrapods (i.e., a greater distance would result if the tape were 

 placed over the highest points on the tetrapods) . 



The top margin of the barnacle- limpet zone served as the ref- 

 erence point for all distance measurements taken during the associ- 

 ation mapping phase of the project. Distances to association bounda- 

 ries measured down the slope of each side of the island were multi- 

 plied by the sine of the average slope for each side. These cor- 

 rected distances were plotted in Figures 9 to 12 and Figures C-3 to 

 C-6. 



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