Abstract
The giant kelp (Macrocystis pyrifera) is an ecosystem engineer that creates complex three-dimensional habitats and is a major source of primary productivity for coastal ecosystems. Macrocystis pyrifera kelp forests globally are in decline. This is occurring at rates four times faster than tropical terrestrial forests and has resulted in losses of ecological, economic and cultural values provided by Macrocystis pyrifera forests. Efforts to restore kelp forests both passively, by ameliorating stressors or modifying substrata, and actively, with cultivation and transplantation techniques have been developed in recent years. By examining changes in distribution, exploring environmental factors in existing and extinct kelp forest sites, and evaluating the effectiveness of different restoration techniques, this thesis investigated the environmental conditions affecting Macrocystis pyrifera populations and their implications for restoration efforts in Aotearoa, New Zealand.
It was found that Macrocystis pyrifera has continued to decline overdeclined from the west in the Marlborough Sounds region. This continues a trend observed from previous studies between the 1940’s to 1988 and Macrocystis pyrifera has been lost from 54km of the coast compared to the 1940s and a further 13km decline compared to 1980s surveys. This trend was also discovered to be occurring in the Stewart Island region. This eastward retreat is associated with elevated sea surface temperature in the Tasman Sea. Environmental monitoring that compared light, temperature, and salinity, at an existing and extinct kelp forest in Otago, New Zealand, found similar abiotic conditions suspecting other factors such as periodic disturbance leading to, changes in substratae, and competition with turf dominated communities, are likely attributable toresponsible for historic losses of kelp and prevention of reestablishment.
Experiments comparing different substratae materials for kelp cultivation found that materials influence the settlement density and early development of Macrocystis pyrifera. The physical and chemical properties of these substrataes are likely responsible for these differences but site-specific conditions appear most important for survival post outplanting. The restoration trials, as the first of their kind in southern New Zealand, provide a baseline for future efforts and highlight the adaptability required to tailor restoration methods to local environmental conditions. While restoration methods may be effective given the right conditions, profound changes in sedimentation in coastal waters of New Zealand is likely necessary for long term success. Ultimately, this work advances our understanding of M. pyrifera and offers valuable knowledge to inform more effective kelp forest management strategies in a changing environment.