Dissertation Abstract

Population and community impacts of extreme events in coastal marine ecosystems

Jurgens, Laura J  2015  

Evolution and Ecology, University of California at Davis (United States), 148 pp.

A worldwide upsurge in extreme events, including heat waves, storms and harmful algal blooms (“red tides”) linked to anthropogenic global change, poses escalating threats to species and ecosystems. Climate change scientists increasingly recognize that such rapid, severe perturbations may have even more severe ecological consequences than gradual shifts in stressors such as temperature and ocean chemistry. Using an approach that integrates ecomechanics, community ecology and animal physiology, I explore how the physical structure of habitat-forming species influences population risk from extreme climatic events. I also examine spatial patterns in the severity of a mass mortality event across multiple invertebrate taxa to establish baselines for investigating factors affecting recovery trajectories after acute disturbances.

I approach these questions in high-biodiversity rocky shore ecosystems that regularly experience environmental extremes as they oscillate between terrestrial and marine conditions with the tides. Through three linked studies that span centimeter to latitudinal spatial scales, I examine how physical effects of widespread habitat-forming species influence organism-scale climate and population risk from extreme heat and desiccation during low tide. I find that the intensity of thermal stresses is dramatically modified by mussel bed and seaweed microhabitats only a few centimeters deep. Without thermal buffering inside the mussel bed, small size classes of juvenile mussels would not survive current climate variation in the areas they inhabit, but mussel beds can also exacerbate thermal stress for organisms living at their surfaces (Chapter 1). I then compare the thermal effects of mussel bed and seaweed turf habitats to those of shore elevation and latitude — typically considered the factors that most influence mortality risk from heat on rocky shores. I find that buffering effects of biogenic habitats influence thermal stress exposure more than shore elevation or climatic shifts over 14° of latitude (Chapter 2). Mussel bed habitats also provide critical refuge from lethal desiccation for resident invertebrates by increasing water vapor pressure relative to exposed bedrock habitats during low tide, and I find that desiccation can be a more proximate cause of mortality from high temperature exposure than strict thermal effects alone (Chapter 3). In Chapter 4, I explore the spatial scale and severity of mortality in marine invertebrates following an exceptional disturbance event associated with a harmful algal bloom. I find that the combination of unusually severe mortality and large spatial scale, coupled with divergent life histories among affected species, are likely to drive strong differences in recovery trajectories.