Effects of sewage effluent on the population structure of Brachidontes rostratus (Mytilidae) on a temperate intertidal rocky shore

A single polluted site at Boags Rocks, south-eastern Australia, and four co ntrol sites were used to evaluate the effect ofsecondary-treated sewage eff luent on the population structure, recruitment, growth and mortality of the mussel Brachidontes rostratus. B. rostratus recruited in greater numbers t o mussel clumps at the outfall site than at control sites, regardless of th e origin of the mussel clumps. The effects of pollution on the soft tissue mass and shell growth of juveniles depended on the origin of the mussels; s hell growth of mussels local to Boags Rocks was smaller than the average sh ell growth recorded in mussels at the control sites, and individuals transp lanted into Boags Rocks had higher soft tissue mass than those at the contr ol sites. Mortality was greater at the polluted site than the control sites , regardless of mussel origin. Changes in the population structure of B. ro stratus as a result of the discharge of sewage effluent have implications f or intertidal fauna that use the habitat created within mussel clumps.