Content area
Full text
INTRODUCTION
The study of community organization patterns is essential in ecology as it provides a descriptive basis to further develop hypothesis, build models, design experiments or perform monitoring fieldwork. Using the appropriate methodology is fundamental to obtain an accurate description of the assemblages as well as qualitative and quantitatively representative samples (Bellan-Santini 1963, Boudouresque 1971, Martin et al. 1993). The optimum and feasible sampling method is ultimately determined by the type of information needed, together with the material and time resources available. The selected methodology has to optimize the balance between obtained information and working effort.
SCUBA diving allows marine scientists to study benthic assemblages in situ by means of a wide variety of sampling methods. Dredging and other similar remote techniques used on soft bottoms are not appropriate for rocky bottoms as they provide incomplete information of the system (Russell 1990). Therefore, rocky bottoms at relatively shallow depths are often studied by SCUBA diving, which can provide qualitative and quantitative data for statistically elucidating distribution and abundance patterns of species (Littler and Littler 1985). There are two main types of technique: a) destructive techniques that imply the partial removal of the assemblages and b) non-destructive techniques that leave the assemblage undamaged.
The classic destructive method consists in scraping and collecting all existing organisms of a known area (Bellan-Santini 1963, True 1964, Boudouresque 1971). The organisms are later identified and quantified in the laboratory. Numerous descriptive studies have used this methodology in the Mediterranean Sea (Romero 1981, Airoldi et al. 1995, Ballesteros et al. 1998 among others), Western Europe (Niell 1979), Africa (John et al. 1977, McQuaid 1985), North America (Mann 1972, Calvin and Ellis 1978) and Asia (Sakai 1977).
Non-destructive direct methods use quadrats of a specific area to estimate the species cover percentage or frequency. Data are estimated in situ using sub-quadrats (area, Dethier et al. 1993, Parravicini et al. 2010, Bertocci et al. 2012) or point-quadrats (contact points, Foster et al. 1991, Dethier et al. 1993, Benedetti-Cecchi et al. 1996). Data are obtained almost immediately but the results depend on the previous taxonomical knowledge of the diver. These methods are less precise than the scraping technique but are faster, allowing larger areas to be sample and more replicates to be collected. They...