Soft sediments are complex habitats. They include physical components, such as different sized mineral grains, biological components, including microbes, faunaand flora, plus chemical components, such as tracemetals. Different components of sediments are variable in space and time, with some components likely to be more stable than others. For example, large plants, such as seagrasses, can form relatively extensive meadows which may be relatively stable through time, unless disturbed , whereas micro-algae are more variable . Similarly, although there may be small-scale variation in grain-sizes within a location, coarse-grained beaches and fine-grained mudflats are usually distinct and persist through time.