ABSTRACT. – Using a comprehensive approach, three intertidal sites in East Sussex UK were analyzed for their environmental quality by assessing the health of the local population of blue mussels (Mytilus edulis Linnaeus). During a six month sampling period mussel populations were monitored on site; additionally, a set of biomarkers, comprising lysosomal membrane stability and in vitro fertilization success were assessed. Data were analyzed in relation to physical seawater variables, salinity (psu), dissolved oxygen (DO), temperature and total dissolved solids (TDS) in order to determine the overall health status of mussels at respective sites. Mussels from all three intertidal sites showed clear signs of stress. Furthermore, slight variations of environmental variables such as oxygen and salinity clearly influence the physiological responses in mussels, with reduced gamete survival being of extreme concern.