'Abundance scales' are semi-quantitative estimates of numbers or cover of conspicuous plants and animals. These scales were first devised by Crisp and Southward (1958) and were used by Ballantine (1961) in deriving his biological exposure scale. Crisp and Southward's six broad categories are still used today and are given below. Since then, other workers have added categories but this does not always result in increased accuracy (Hawkins and Jones, 1992). See also Moyse and Nelson-Smith (1963), and Crothers (1976). Similar scales can be devised for species in sand or mud if their presence is readily apparent from burrow openings, tubes or casts, e.g. Arenicola marina, Lanice conchilega, Scrobicularia plana, Corophium arenarium. Crisp and Southward categories:
A = Abundant C = Common F = Frequent O = Occasional
E = Extremely abundant S = Superabundant
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