Mixed fractals and anisotropy in subantarctic marine macroalgae from south Georgia: Implications for epifaunal biomass and abundance

Fractal dimensions (D) of image perimeters of 4 macroalgae (Macrocystis pyrifera, Desmarestia menziesii, Schizoseris condensata, Palmaria georgica) collected at South Georgia, Southern Ocean were established over a wide scale range. For 3 species (M. pyrifera, S. condensata, P. georgica) cross-frond D was also estimated. At large scale all species showed complex perimeters (D 1.26 to 1.83, depending on species), but showed reduced complexity (low D) at small scale, and so have mixed fractal characteristics. Cross-frond D was low in the 3 species studied, indicating anisotropy, and was markedly low in P. georgica which has extensive, smooth, flat fronds. Epifaunal community analysis demonstrated that epifaunal abundance and biomass were related more to the scale at which complexity occurs than degree of complexity itself. S. condensata and D. menziesii (particularly complex, high D) show high epifaunal abundance and biomass and a predominance of large animals; M. pyrifera and P. georgica (simpler, lower D) have low abundances and biomasses and the epifauna is dominated by small animals. M. pyrifera is fairly complex (D ca 1.3) at scales above 50 mm; its complexity will impinge on fish, birds and mammals, not epifauna. M. pyrifera beds have a perimeter D (ca 1.4) similar to those of convoluted coastlines.