ABSTRACT
Because of the variety of possible sources, and of the synergistic effects of environmental and biological processes in controlling the distribution and dynamics of sediment particles, the nature and amount of sediments that are present on rocky coasts is highly variable in space and time. Sediments can be clay, silt, sand or detritus, may have variable composition and grain size distributions, and may or may not include pollutants. They may occur as a thin stratum, or form deposits centimetres to tens of centimetres thick, and may or may not turn into compact, impermeable layers. They may accumulate locally or be resuspended and transported above the substrata, depending on local hydrodynamic and topographic conditions. Furthermore, high rates of sedimentation are generally accompanied by high levels of turbidity from suspended sediments, and may often be associated with elevated inputs of nutrients or lower levels of salinity, as in the case of river floods (Gillanders & Kingsford 2002). This heterogeneity results in a variety of possible effects on rocky coast organisms, which are often difficult to separate from each other or from the concomitant effects of other environmental factors. Indeed, while in recent years there has been an increasing number of studies aimed at testing experimentally the effects of sediments on rocky coast organisms and assemblages, very few attempts have been made to try to clarify and separate the mechanisms of action of sediments (but see Devinny & Volse 1978, Marshall & McQuaid 1989, Kendrick 1991, Airoldi 1998, Chapman & Fletcher 2002), and identify the relevant spatial and temporal scales of impact of these different and interacting processes (Airoldi & Virgilio 1998).
