Mass mortality events of echinoderms: Global patterns and local consequences

Wildlife mass mortality events can have profound ecological consequences and may be becoming more frequent or severe due to climate change, anthropogenic factors or other stressors. Mortality events involving echinoderms are of particular concern because of the important role echinoderms play in structuring marine ecosystems. In this thesis I explore the local consequences of a widespread sea star mortality event, and investigate the global trends in echinoderm mass mortality events. I found that the mass mortality of the sunflower sea star Pycnopodia helianthoides, which began in the summer of 2013 as a result of a wasting syndrome, resulted in a trophic cascade involving urchins and kelp at the local scale (i.e., Howe Sound, BC). A global review of reports of echinoderm die-offs revealed that these events have not become more frequent or extensive since 1897. However, disease and climate change may be playing an increasing role. This study provides some of the first evidence of subtidal community shifts following sea star wasting syndrome, and highlights the need for consistent and comprehensive documentation of echinoderm population trends in the literature to increase our understanding of mass mortality events.