The early life stages of Hormosira banksii can be viewed as a series of distinct developmental events such as gamete release, fertilization, germination, adhesion, cell division, apical hair formation and growth. These developmental stages can be targeted for experimentation as well as used as a measure of health in bioassay tests. Three bioassays were devised and compared to determine which developmental events in H. banksii are most susceptible to effluent (40%) and/or reduced salinity (21‰ S). These treatments approximate conditions in the shore zone where H. banksii once occurred at Boags Rocks, Victoria, Australia. Reduced salinity and sewage effluent affected developing H. banksii differently. Damage caused by reduced salinity occurred within the first 48 h and affected fertilization and germination. Exposure to sewage effluent did not affect fertilization but reduced the number of healthy embryos that had formed a wall by 24 h, germinated by 48 h and divided by 72 h. Both sewage effluent (40%) and reduced salinity (21‰ S) significantly decreased the number of healthy developing embryos that had adhered by 24 and 48 h.

Phenolic compounds, packaged within vesicles known as physodes, are a major cytoplasmic constituent of eggs and zygotes of the Australasian fucoid Hormosira banksii. Physode movement in early life stages of Hormosira is described. We have used the cytoskeletal inhibitors cytochalasin B, latrunculin B and nocodazole added during different stages of development to investigate the role of the cytoskeleton in movement of these vesicles to regions of active wall formation in the growing rhizoid tip and the plane of cytokinesis prior to cell division. Actin inhibition prevented polarization, cross-wall formation and physode movement. When microtubules were disrupted polarization was still possible, but cross-wall formation and physode movement were prevented. Both actin microfilaments and microtubules are necessary to move physodes to regions of accumulation and active wall formation.