Fractal characterization of Mytilus edulis L. spatial structure in intertidal landscapes using GIS methods |
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Authors: | Thomas W Crawford John A Commito Ann M Borowik |
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Institution: | (1) Department of Geography, East Carolina University, Brewster A-234, Greenville, NC 27858, USA;(2) Department of Environmental Studies, Gettysburg College, PA, USA;(3) Present address: NOAA National Ocean Service, Biogeography Team, Silver Spring, MD, USA |
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Abstract: | The blue mussel, Mytilus edulis L., forms dense and variable patch mosaics composed of aggregates of mussel individuals. Knowledge of mussel bed spatial
pattern at multiple scales is important for understanding the form and function of intertidal systems where mussels are prominent
features. This study extends prior work demonstrating fractal patterns of mussel boundaries in soft-bottom systems at the
quadrat-scale by investigating fractal structure using GIS methods at both the quadrat- and bed-scales. The study pursues
three goals for mussel beds in eastern Maine: (1) to compare quadrat-scale fractal dimensions obtained using manual methods
with those obtained using digital imagery and techniques, (2) to determine if fractal patterns identified at the quadrat-scale
are also present at the bed-scale, (3) and to evaluate the effectiveness of aerial photography and image analysis techniques.
Photographs of randomly located quadrats (2500 cm2 each) were scan digitized and classified into mussel presence/absence classes. Fractal dimensions of mussel/non-mussel boundaries
were calculated using the box-counting method and compared with results obtained using analog photographs and methods. Digital
aerial photographs at low tide were acquired for beds at two sites and classified using image processing techniques, and bed-scale
fractal dimensions were calculated. At the quadrat-scale, fractal dimensions and their relationship with percent cover differed
consistently in absolute value from results using manual methods but agreed in demonstrating fractal patterns for all quadrats
and a parabolic trend with percent cover very similar to the one revealed manually. At the bed-scale, both sites were shown
to be fractal, with higher dimension value for the bed that subjectively appeared more fragmented and highly dissected. Because
mussels are important soft-bottom ecosystem engineers, i.e., foundation species that regulate species composition and abundances,
the fractal spatial distribution identified in this study suggests that the species affected by them also exhibit fractal
patterns. These results indicate the effectiveness of archive imagery and GIS methods for characterizing intertidal systems
and point to the feasibility of future image acquisition. |
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Keywords: | Benthic structure Blue mussel Fractal dimension Image processing Multi-scale Mussel bed Quadrat Soft-bottom Spatial pattern |
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