Eelgrass as a Bioindicator Under the European Water Framework Directive

Abstract

Eelgrass is the most widespread plant in temperate coastal waters. It is regarded as a useful indicator of water quality because water clarity regulates its extension towards deeper waters, i.e. the depth limit. This study analyses the use of eelgrass depth limits as a bioindicator under the Water Framework Directive (WFD). The WFD demands that ecological status is classified by relating the actual level of bioindicators to a so-called ‘reference level’, reflecting a situation of limited anthropogenic influence. The directive further demands that reference levels are defined for ‘water body types’ with similar hydromorphological characteristics, and that the classification thereby becomes ‘type-specific’.