Echinoderms in decline: modeling trends, assessing consequences, and reversing course

Humans are having myriad direct and indirect effects on marine species. Echinoderms appear particularly prone to dramatic population declines and extirpations driven by both disease and anthropogenic stressors like fishing. Here, I examine how we estimate the magnitudes of these declines, their ecological impacts, and processes by which we can begin to reverse them. In Chapter 2, I assess the magnitude of decline of the Sunflower Sea Star (Pycnopodia helianthoides) in Canada by jointly analyzing quantitative data from formal scientific surveys with semi-quantitative observations from community-sourced data. I found that Sunflower Sea Star abundance has been reduced by 82.1% (95% credible interval: 76.0% : 87.2%) following the onset of sea star wasting disease in 2013. My approach provides a scaffolding for future at-risk species assessments that allows us to harness a greater diversity of data sources, and therefore reduce uncertainty in the conservation decision-making process. In Chapter 3, I move beyond identifying declines to examining their impacts. I use a large-scale field experiment to test whether the loss of sea cucumbers through simulated fishing affects seagrass productivity in a natural system. While I did not detect a change in overall patch-level seagrass productivity, I found that individual leaf extension rates were ~15% lower at sites where all sea cucumbers were removed. These findings demonstrate the importance of using multiple response metrics and scales in attempting to quantify consumer-mediated effects on primary productivity. In Chapter 4, I further explore the role of spatial scale in our understanding of population declines by assessing the state of the commercial sea cucumber fishery in British Columbia. By downscaling stock assessment analyses to spatial scales that better reflect those at which commercial harvesters interact with sea cucumbers, I found that data aggregation in stock assessment has masked substantial localized population declines. These findings reconcile disparate perceptions among harvesters and federal managers and provide managers the chance to redirect the course of the fishery before it is too late. Together, these chapters highlight the importance of drawing on multiple lines of evidence and considering the impacts of scale in addressing conservation challenges.