Intertidal fucoid algae can function as ecosystem engineers across temperate marine regions. In this investigation, we assessed the function of the alga dominating rocky reefs in temperate Australia and New Zealand, Hormosira banksii. Invertebrate and algal species assemblages were examined within areas of full H. banksii canopy, areas where it was naturally patchy or absent (within its potential range on the shore) and areas where the intact canopy was experimentally disturbed. Differences in species assemblages were detected between areas with natural variation in H. banksii cover (full, patchy, negligible), with defined species associated with areas of full cover. Differences were also detected between experimentally manipulated and naturally patchy areas of canopy cover. Species assemblages altered in response to canopy manipulations and did not recover even twelve months after initial sampling. Both light intensity and temperature were buffered by full canopies compared to patchy canopies and exposed rock. This study allows us to predict the consequences to the intertidal community due to the loss of canopy cover, which may result from a range of disturbances such as trampling, storm damage, sand burial and prolonged exposure to extreme temperature, and further allow for improved management of this key autogenic ecosystem engineer.

Controlling the invasive species Undaria pinnatifida remains a worldwide issue with very few successful eradications reported. Following the detection of U. pinnatifida within a Marine Protected Area in Victoria, Australia, in 2017, an ongoing management program was implemented, with monitoring occurring until 2022. Following a resource intensive effort in 2017 (estimated average of 330 in‐water hours), a suppression phase from 2018 implemented a reproductive sporophyll excision removal method, which aimed to reduce manual handling (estimated average of 280 in‐water hours from 2018 to 2022), U. pinnatifida reproductive output and spore spread. U. pinnatifida abundance and sporophyll size was monitored to identify optimal time of year to target removal efforts. Sessile species assemblage was also monitored to identify any changes that could be linked to U. pinnatifida abundance. Between late winter and late spring, U. pinnatifida abundance was generally highest, with senescence observed in summer. Less plants were observed in Autumn, with new cohorts generally emerging in winter. Reproductive sporophylls developed quickly, and were found in all seasons, with the largest most frequently in spring. This study found that the management should target removal efforts is in winter and spring, to reduce the number of future generation plants. U. pinnatifida had no identifiable impacts on native species assemblages, which remained similar through time. This study demonstrates the effectiveness of high effort removal of U. pinnatifida followed by sustained invasive species control at preserving natural values in a marine protected area.