Interspecific competition, recruitment inhibition, and potential kelp-kelp phase shifts – implications for conservation and function in a climate change hotspotResistance, Resilience and Phase Shifts

Cayne Layton¹, Scott Bennett¹, Hunter Forbes¹, Craig Johnson¹, Scott Ling¹, Elisabeth Strain¹, Jeffrey Wright¹

¹University of Tasmania, Australia

Tasmania’s marine environments and reef systems are experiencing a period of unprecedented climate-driven change. Floating canopies of giant kelp (Macrocystis pyrifera) were once a ubiquitous feature of the Tasmanian coastline but have declined by >95% since the 1960s. In response, there is a growing effort to conserve these iconic ecosystems and the biodiversity they support. Also native to Tasmania is the common kelp (Ecklonia radiata), which is more thermally tolerant than giant kelp and has increased in cover in Tasmania over the past several decades, presumably filling space left behind by the declining giant kelp. Yet, it seems that these changing interspecific dynamics may not only be a response to giant kelp loss but also be a mechanism through which the dramatic declines of giant kelp are realised and/or reinforced. Here, we share results from several field studies – including ‘forest-scale’ restoration trials and Macrocystis and Ecklonia recruitment experiments – and discuss how interspecific competition and recruitment inhibition may be facilitating a potential kelp-kelp phase shift, whereby ocean warming, seasonal pulse disturbances to Macrocystis, and Ecklonia stability and demography, may be altering kelp dynamics and function in the region. This changing environment also generates a suite of intriguing socioecological questions regarding species of preference, the setting of conservation priorities, and the future proofing of restoration activities. Ultimately, it has never been more critical to understand the shifting dynamics of this system whilst also looking forward at the ongoing and forecast changes and stressors in the region.