Anthropogenic influences on community structure

Table 2  Summary of anthropogenic influences on community structure
Physical disturbance
Physical disturbance by trampling can impact significantly on rocky shore communities. Disturbance of rock communities in the subtidal is generally less marked. Activities such as fisheries for crabs and lobsters tend to result in only limited changes in the balance of species composition within biotopes but may rarely result in significant shifts in community composition. Where dredging (e.g. for scallops) occurs close to rocky habitats, delicate species can be damaged.
Disturbance of sediment types is widespread, particularly through benthic fisheries activities and aggregate extraction; such disturbance can have significant effects on community composition and may, in some cases, result in completely altered biotopes compared with fully natural conditions. Areas subject to prolonged sedimentary disturbance may exhibit highly variable, sub-climactic communities.
Severe pollution may reduce species richness (pollution effects are not well studied).
Pollution may reduce species richness, encourage higher densities of opportunist species, e.g. capitellid polychaetes, or alter community structure.