Climate change exerts a profound impact on marine ecosystems, with coastal environments uniquely affected by both oceanic and terrestrial influences. In coastal areas, oceanic drivers, such as rising temperatures and altered circulation patterns, combine with terrestrial inputs like changes in freshwater inflow to create unique environmental conditions. Beyond the gradual warming of ocean temperatures, the increasing occurrence of extreme temperature anomalies poses considerable threats to ecosystem stability, necessitating detailed investigations into their underlying mechanisms and ecological consequences. This thesis focuses on how climate change manifests in Doubtful Sound, a temperate fjord characterized by rocky subtidal benthic communities. First, using an 18-year high resolution dataset, I investigate the spatiotemporal trends in temperature and salinity throughout Doubtful Sound. I analyse the fjord’s temperature dynamics spatially, spanning from 0.5 m to 19 m and from the inner fjord to outer fjord. Linked with climate change, I identify increasing mean temperatures and increases in temperature anomalies. Furthermore, I report the occurrence of two marine heatwaves in Doubtful Sound. Lastly, I note a deepening of the low salinity layer, a key physical feature that drives the structure and stability of benthic communities in this fjord. Coupled with these oceanographic analyses, I explore spatial and temporal drivers of the benthic communities in Doubtful Sound. I document higher diversity and variability in the outer sites as compared to the inner sites. Additionally outer fjord communities show significant shifts in benthic community composition through time, while the inner fjord communities remain largely constant. Though a range of factors influence the abundance of benthic organisms including biotic interactions, salinity levels and physical disturbance, thermal profiles provide insights into the potential sensitivity of taxa to warming oceans. By linking benthic abundance with temperature trends, I identify potential thermal thresholds for several key taxa. In the shallow waters for example, barnacles and mussels peak in abundance at 15.5-16 °C and sharply decline in higher temperatures. Conversely, encrusting sponges increase dramatically in response to warming temperatures. Lastly, I investigate the role of the 2018 Tasman Sea marine heatwave in structuring the benthic community in Doubtful Sound. Minimal impacts on the benthic community after the heatwave were recorded, although notable increases in green algae and encrusting sponge were observed at two sites. The final chapter of this thesis investigates how environmental changes associated with climate change, specifically increased temperature and decreased salinity, influence the fitness of Coscinasterias muricata, a keystone predator in Fiordland’s subtidal ecosystems. I designed a laboratory experiment to identify the effects of temperature, salinity, and the interaction between the two on the fitness of C. muricata. Righting trials, a well-established proxy for fitness, were carried out to investigate the effects of altered physical conditions. Interestingly, only salinity had a significant effect on C. muricata fitness, highlighting the potential of low salinity events to affect benthic communities in estuarine environments. Overall, this thesis underscores the multifaceted impacts of climate change on fjord ecosystems, emphasizing the importance of physical anomalies beyond increases in mean temperature. These findings highlight how increasing anomalies and shifts in temperature and salinity regimes can profoundly influence the structure and dynamics of benthic communities. By integrating long term environmental data with experimental insights, this work advances our understanding of the complex interactions between climatic drivers and ecological responses, providing critical perspectives on the vulnerability and resilience of temperate fjord ecosystems under changing physical conditions.