Coastal lagoons and estuarine environments are naturally stressed systems due to their high physicochemical variability (Elliott & Quintino, 2007). The species living in these environments are tolerant to such stress, adapting their physiology and behaviour to a broad spectrum of fluctuations. Thus, like communities in the initial stages of ecological succession or contaminated by human activity (Odum, 1969; 1985), estuarine benthic communities are expected to show low diversity, with few species of small size, very abundant, and typical opportunistic r-strategists (Margalef, 1969; Michel, 1979; Barnes, 1980; Kjerfve, 1994; Carrada & Fresi, 1988; Reizopoulou & Nicolaidou, 2004). The communities would then be controlled by the physical environment, and the interspecific relationships would not be very developed (Sanders, 1968). Therefore, estuarine ecosystems are expected to be conformed by a simple and uniform benthic community represented by the euryhaline and eurythermal biocoenosis described by Pérès & Picard (1964). Such acceptation of uniformity has been maintained through time by different authors (Augier, 1982; Carrada & Fresi, 1988; European Environment Agency, 2015; Gubbay et al., 2016), habitat lists, and conservation agreements (OSPAR, Barcelona or Eunis).