Brackish grazing marsh systems are naturally poorer in species than freshwater systems, so this difference needs to be taken into account during site evaluation. As many grazing marshes are situated near the coast, their ditches often support invertebrates tolerant of salinity. Salt-tolerant invertebrate species that can be used as indicators of brackish conditions are given a score in this index, based on a scale of 0 (least tolerant of saline conditions) to 2 (dependent on at least mildly saline conditions).
It is important to note that this index is applicable only to ditches in coastal grazing marshes and floodplain grazing marshes near the coast, in England and Wales.
- Score 0 - Freshwater species tolerant of only mildly brackish water. These are not routinely found more often in brackish than in fresh conditions, or close to the coast rather than inland.
- Score 1 - Species tolerant of mildly brackish conditions. These are found more in brackish conditions than in completely fresh water, or near the coast more often than inland.
- Score 2 - Species that are obligately dependent upon mild to moderately brackish conditions. These are absent from completely fresh water except as strays from nearby brackish sites.
For more information see: Palmer, M., Drake, M. and Stewart, N. (2013) A manual for the survey and evaluation of the aquatic plant and invertebrate assemblages of grazing marsh ditch systems Version 6. Buglife report.