Durvillaea antarctica (Chamisso) Hariot and D. willana Lindauer are massive brown algae of the lower littoral and upper sub-littoral respectively on the most exposed New Zealand coasts. Aspects of the reproductive biology of Durvillaea have been studied and these have been related to results of clearing experiments. Observations at two localities 600 km apart on the South Island east coast showed that gametes were released from May to October, and that young plants appeared over a much shorter period. On rocks cleared of D. antarctica in mid winter up to 7,000 recolonising plants per m2were counted, whereas on rocks cleared at other times there was little, if any regrowth of Durvillaea and a sequence of other algae occupied the cleared area. When all plants were removed and successful recolonisation followed, the upper limit was appreciably lower than before. The density of young plants was highest on sites where old holdfasts had been scraped off. Changes in density, size-structure and growth-rates of recolonising plants are described and briefly compared with measurements of natural populations and plants in areas where only large plants were removed, and smaller ones left. These field experiments have clear implications for proposed commercial harvesting. © 1979, Walter de Gruyter
