The fractal geometry of Mytilus edulis L. spatial distribution in a soft-bottom system

The blue mussel, Mytilus edulis L., forms dense beds that cover extensive areas of the seafloor. Mussel bed spatial pattern often appears to be complicated and highly irregular. In this study, fractal geometry was used to characterize the spatial distribution of mussels in a population from Maine, USA. Hypotheses were tested that related fractal dimension, D, to percent cover, density and spatial dispersion. The first hypothesis was that the outline of the M. edulis pattern is fractal, i.e., D values lie between 1 and 2. The second and third hypotheses were that fractal dimensions reach their highest values at intermediate levels of M. edulis percent cover and density. The fourth hypothesis was that the relationship between fractal dimension and the degree of M. edulis aggregation is negative. All four hypotheses were supported. D values of the spatial pattern within quadrats ranged from 1.36 to 1.86. Second order regression curves in the form of downward-opening parabolas were found between D and percent cover ( r 2=0.94) and density ( r 2=0.92). A negative linear regression existed between D and Morisita's Index of spatial dispersion ( r 2=0.82). The results indicate that the complex distribution of mussels within beds is spatially ordered and has a predictable pattern that is revealed by fractal geometry.