There are many potential indicators (Table 1) but few threshold values that define significant
changes to fish habitat. Methods and thresholds are available for bio-geochemical indicators,
such as total free sulfides and redox potentials in soft sediments, to assess the degree of
organic enrichment in the immediate vicinity of bivalve operations and to be applied in
operational monitoring programs. Sediment imaging techniques have also been used
successfully to assess physical and biological habitat structure and provide qualitative and
some semi-quantitative information on potential bio-geochemical changes.