Fractal characterization of Mytilus edulis L. spatial structure in intertidal landscapes using GIS methods

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.     

软、硬底质网箱对克氏原螯虾养殖效果分析

以体质量(8.02±1.65)g克氏原螯虾(Procambarus clarkii)为研究对象,探讨软、硬两种不同底质网箱对克氏原螯虾养殖效果的影响。试验分为两组,软底网箱作为对照组,硬底网箱为试验组,每组设3次重复,每个网箱随机放养60尾螯虾。养殖6周后,测定克氏原螯虾的各项生长性能指标和酶活力,分析了软、硬底质网箱中克氏原螯虾生长和生理指标的变化特征。结果表明:试验组克氏原螯虾的终末体重、存活率、饲料效率、增重率和特定生长率均显著高于对照组,而残肢率显著低于对照组;同时,各项消化酶和抗氧化酶活力也明显高于对照组。由此可知,采用硬底网箱进行克氏原螯虾养殖的效果较软底网箱更好。