Abstract
Climate change is impacting biodiversity globally threatening ecosystem functioning. Using in situ heated settlement panels in New Zealand, this research aimed to assess the response of benthic marine communities to warming without eliminating the impact of natural variation. Heated settlement panels allow for controlled manipulation of temperatures in situ and can be used to assess community response at the individual, species, and community-levels. The heated settlement panels were monitored using high-resolution photography for three-month periods, allowing for species to be traced through time. The results indicated that warming of 1°C led to widespread increases in growth rates, while growth responses under 2°C of warming were more variable (Chapter Two). Survival rates were highly species-specific, however total survival on the panels showed a moderate correlation with temperature. In situ warming indicated that competitive encounters can be expected to shift in future conditions (Chapter Three), alongside shifts in community assemblage and structure (Chapter Four). This thesis presents evidence of community reshuffling under warmed conditions (1°C and 2°C above ambient) occurring through shifts in alpha and beta diversity, reduced competitive complexity, and a shift in the dominant space-occupier between ambient and heated panels. Prime examples of this shift include the increased growth and coverage of the colonial ascidian Lissoclinum perforatum and the bryozoan Rhynchozoon zealandicum under conditions warmed by 1°C, both of which were influential species contributing to the dissimilarity between heated and ambient treatments. In contrast, Calloporina angustipora the spatially dominant species on the ambient panels, presented seasonally specific reduced growth and occurrence under heated treatments. Early dominance of colonial species can shift the mechanisms which maintain diversity, leading to long-term adjustments in the structure and assemblage of these communities. Chapter four further indicates an increased phylogenetic clustering under warmed treatments, suggesting environmental filtering towards warm affiliated species. Chapter Five presents evidence of seasonal acclimation in ascidian species in the region, but little evidence of treatment-based acclimation. As a whole this thesis suggested that marine encrusting communities in iv communities in the Otago region will experience assemblage-level adjustments under near future warming, further, highlighting the importance of considering climate change in an environmentally relevant context.