Abstract
Macrocystis pyrifera (M. pyrifera) is an ecosystem engineer. It modifies the environment providing the foundation, food, resources, and habitat provisions for many other organisms. Globally, kelp forests have been declining due to multiple-stressor impacts. Anecdotally, M. pyrifera has declined in Otago, New Zealand however no research has yet assessed this. The aim of this study was to determine changes in extent of M. pyrifera along coastal Otago to understand if there has been a change in living memory of local knowledge holders. The research then aimed to validate evidence given by interviewees and investigate what habitat remains for the potential of future regeneration of the kelp forests in this area. During 19 semi-structured interviews, local knowledge holders reported a complete loss of M. pyrifera forests along the southern coastline north of Taieri Island that occurred between approximately 1970’s – 1980’s. This stretch of coastline is still referred to as “The Kelp”, even by interviewees who never observed M. pyrifera here. The area indicated by interviewees at the entrance of the Taieri River was investigated further. A multibeam survey located the presence of two reef structures (0.2 km2 and 0.9 km2) in the location indicated by interviewees. The two reef structures appeared to have hard substrate in a depth range (9 – 21 m) that could support M. pyrifera, if other environmental conditions were congruent. A drop camera survey of the two reef structures was done to investigate the substrate and biological compositions of the reef structures. This was compared to a previous survey that had been completed in the East Otago Taiāpure where it is known that there is still M. pyrifera. The camera analysis supported the multibeam survey, that there was sufficient hard substrate to support M. pyrifera. Assessment of the algal composition showed a homogenous mix of coralline, C. brownii and mixed red algae when compared to the heterogeneous canopy and understory composition of the East Otago Taiāpure. Along both the northern and southern coastlines there was an agreement amongst interviewees that runoff from the land, in particular sedimentation, was a key driver behind the changes observed. This fits both with the increases in fine sediment from land use observed around Otago as well as the presence of sediment resilient species of algae. To further understand the implications of the loss of kelp forests along this coastline it would be essential to quantify the stressors that have caused the loss of kelp along this coastline and if these stressors are still present in this environment. In a changing global environment, it is important to understand the changes that have, and will continue to occur in order to do valuable ecosystem-based management.