Ecological diversification in habitat use by subtidal triplefin fishes (Tripterygiidae)

Recent work has shown that habitat specialisation can lead to diversification in lacustrine and marine fish species. Here we investigate specialisation in the New Zealand triplefin fish fauna (Tripterygiidae), which has the greatest diversity and disparity of triplefin species in the world with 26 endemic species. Most species are sympatric throughout coastal New Zealand, showing no obvious latitudinal trends in abundance. We sampled habitat use quantitatively, and microposition qualitatively, in 17 triplefin species at 151 sites representing a geographic range from 35 degrees 50'S to 46 degrees 70'S. A novel Euclidean-distance non-metric multidimensional scaling (MDS) technique was used to display the quantitative habitat variables (depth, fetch, rock, cobble, gravel, sand, mud, macroalgae, and coralline and turfing algae) of each species. For each species, the positions of these variables were compared to those of all species using Procrustes configural matrix comparison methodology, which resulted in a final 3D spatial representation of species using non-metric MDS. Our results demonstrate that triplefin species have diversified considerably in habitat and microposition use, resulting in species occupying different patches in the same general location. Strong habitat partitioning was shown by 3 distinct clusters of species along a gradient of depth and exposure. Some species showed an even finer sub-partitioning by using different substratum types, in particular rock and mud. Correspondence Analysis of microposition data showed that 5 species differed from all other species, further partitioning habitat use. Thus, our results suggest that habitat use has been important in the diversification of New Zealand triplefin fishes.