Using Zostera noltei biometrics for evaluation of the ecological and environmental quality status of Black Sea coastal waters

A wide range of seagrass biometrics as well as environmental variables are currently used for classification of the ecological status of coastal water bodies in accordance with the Water Framework Directive (WFD). The use of extensive sets of indicators provides a satisfactory assessment of environmental quality statuses, but also requires substantial amounts of additional laboratory efforts and costs. In this study, typical population-level and individual biometrics of the dwarf eelgrass Zostera noltei (Hornem.) (shoot density, total biomass, above- and belowground biomass, above- to belowground biomass ratio, leaf length and leaf area) were tested and used in the adaptation and validation of a simplified, easy to apply and cost-effective pollution index (ZnoPI) for evaluation of the ecological and environmental quality status of Black Sea coastal waters in accordance with the WFD and the Marine Strategy Framework Directive (MSFD) criteria. Based on the metrics tested, reference conditions were established and ecological quality ratios (EQR) of the studied areas were calculated. The index validation was based on biological sampling and environmental monitoring of Z. noltei meadows in a variety of ecological conditions along the Southern Black Sea coast of Bulgaria. The environmental condition of the study sites was evaluated with an Integrated Pollution Status (I.P.S.), which combined water column variables (nutrients, chlorophyll-a, suspended particulate matter, transparency) as well as total organic matter content and concentrations of heavy metals in sediments in a single metric. Significant correlation between ZnoPI EQR values and I.P.S. was found (r = 0.917 p < 0.0001), which validated the index for Bulgarian Black Sea coastal waters, and possibly other areas with similar environmental conditions.