Fractal dimensions of marine snow determined from image analysis of in situ photographs

Seventy seven in situ photographs of marine snow ranging in size from 1 to 60 mm were used to calculate one- and two-dimensional fractal dimensions, D₁ and D₂, in order to characterize aggregate morphology with respect to aggregate perimeter and cross-sectional area. The lowest fractal dimension of D₂ = 1.28 ± 0.11 was calculated for marine snow aggregates composed predominantly of a single type of particle (e.g. diatoms or fecal pellets) containing large amounts of miscellaneous debris. Marine snow formed by the aggregation of fecal pellets (D₂ = 1.34 ± 0.16), non-identifiable particles (amorphous, D₂ = 1.63 ± 0.72), and diatoms (D₂ = 1.86 ± 0.13) had increasingly larger fractal dimensions. When combined into a single group, all marine snow aggregates had a fractal dimension of 1.72 ± 0.07. Larvacean houses, formed originally from a single, nearly spherical particle, were found to have a D₂ value close to the Euclidean value of 2. Based on fractal geometrical relationships, D₂ should have been equal to previous estimates of D₃, a three-dimensional fractal dimension. Instead, the D₂ value of 1.72 for the combined group was larger than previous estimates of D₃ of 1.39 and 1.52, probably because of the dominant influence of the diatom aggregates on the combined group. Diatom aggregates had the highest fractal dimensions and covered the widest size range of all categories of particles examined.