Comparison of three methods for quantifying topographic complexity on rocky shores

Abstract

Topographic complexity (TC) is an important factor in determining community structure in aquatic habitats and there are numerous methods for its estimation. Here we assess and compare three (chain, divider and distance-wheel) methods across different users and substrata over scales of 78-1030 mm. All three techniques showed the same basic trend in TC over different substrata. However, the chain took approximately 1.5x as long to use, at larger-scales (>271 mm), as the other techniques and resulted in highly variable TC estimates. The chain and divider techniques both have the potential to miss relevantly scaled TC depending on the survey starting point, a disadvantage not suffered by the distance-wheel. TC measured using the distance-wheel was approximately 1.8x that recorded by the divider technique and significantly (P<0.05) less variable compared with the chain technique. The distance-wheel was rapid and easy to use, superior in accessing awkward topographies and has considerable potential for improvement. It is recommended as a technique for estimating the TC of rock-surfaces at scales >50 mm.