Development of Hormosira banksii (Phaeophyceae) embryos in selected components of secondarily-treated sewage effluent

We investigated the effects of phosphate, ammonium, and a mixture of heavy metals as components of sewage effluent, together with the effects of reduc ed salinity due to sewage effluent discharge into a marine environment, on the development of Hormosira banksii (Turner) Decaisne embryos. The concent ration of each effluent component tested in this study was calculated to ap proximate levels in the shore zone where II. banksii once occurred at Boags Rocks (Victoria, Australia) and the artificial sea medium was diluted to 2 0 parts per thousand S based on average salinity levels measured at this si te. Newly fertilized eggs were cultured in each of these components and com binations of components for up to 7 days. Ammonium, elevated to levels that occur in the vicinity of the outfall, and fresh water, which reduces seawa ter salinity, were the most damaging of the effluent components tested. Osm otically stressed embryos commonly showed swollen chloroplasts, loss of cel l contents, vesiculate cytoplasm, and stunted rhizoid development. Exposure to elevated levels of ammonium retarded embryo development and growth unti l day 7, when cellular damage became evident. The number of damaged embryos was significantly greater when exposed to elevated levels of ammonium adde d to artificial seawater medium diluted to 20 parts per thousand S, The adv erse effects caused by elevated levels of ammonium and reduced seawater sal inity on H. banksii em bryo development could have contributed to the disap pearance of this species from Boags Rocks.