Comparison of field methods for measuring surface topography and their associations with a tropical reef fish assemblage

The relationships between 6 measures of substratum topography or vertical relief and a tropical fish assemblage were evaluated and the merits of the various measures were assessed. A method of quantifying surface topography in the field using a profile gauge is introduced and found to be rapid and to generate concise summary statistics. Of the 6 measures of substratum topography compared, 1 was novel, 2 were derivations of geomorphological techniques and 3 had been previously used in reef fish studies. Measures included the sum of consecutive substratum height differences, vector standard deviation (SD), substratum angle SD, substratum height SD, substratum height coefficient of variation (CV) and the ratio of contoured surface distance to linear distance ('chain-and-tape'). All but the CV were found to grossly differentiate among surfaces that varied in corrugation height and frequency. Consecutive substratum height difference, substratum angle SD and vector SD were best able to differentiate between 9 schematic profiles of varying topography. A field test of the methods was carried out on 100 quadrats (3 X 3 m) from the backreef of Lizard Island, northern Great Barrier Reef, Australia, in which the surface topography, fish and benthic communities had been sampled. The consecutive height difference method performed consistently well, scoring the highest average correlations with total fish abundance, diversity and the abundance of individual species. In an examination of the relationship between the backreef fish assemblage, substratum topography and the cover of benthic organisms, topography was only secondary in importance to depth in describing the patterns of damselfish abundance at the scale sampled.