Benthic fauna - coastal waters

The water status classification of benthos in coastal areas is based on the species composition of the benthic communities, which is a result of the degree of disturbance. The degree of disturbance of a benthic community is assessed by calculating a benthic quality index (BQI) comprising three components: the proportion of sensitive versus tolerant species, number of species, and number of individuals.

The BQI is an indicator frequently used in assessing environmental quality status in relation to the WFD. The use of BQI in Swedish coastal waters has however revealed some weaknesses, in particular in areas where the number of species is low because of permanently low salinity (e.g., the Baltic) or in estuaries with fluctuating salinity. In addition, in shallow exposed areas, such as the open coast of Halland, the BQI could possibly be adjusted for better performance.

Benthic fauna in WATERS
The benthic coastal sub-project within WATERS will focus on refining the BQI in the following respects:

• Further evaluate the sensitivity values of various species to improve the BQI in areas that are stressed because of low salinity and exposed areas.
• Examine whether the refined BQI could be applied in offshore areas. The modified BQI will also be applied to data from Bothnian Bay to examine whether special considerations should be applied to this area.
• Summarize and analyse data and information about sampling methods for shallow waters. Based on that, make recommendations on sampling and methodology.
   

The benthic project will also participate in the planned gradient study together with other sub-projects in which the response to increasing eutrophication will be evaluated on both the Swedish west and east coasts. In these studies, the BQI will be compared with other metrics. The classification according to the BQI will be refined jointly with other sub-projects to harmonize the assessment criteria with other quality elements for coastal waters.

The goal is to improve our knowledge of the sensitivity of various species to various stressors and in this way refine the index. The idea is to add a factor to compensate for natural differences in salinity and substrate. The ultimate goal is to harmonize the BQI with other quality elements used when assessing the ecological water status of coastal waters.