Ecophysiology of Ectothermic Ecosystem Engineers: Bioenergetic Effects of Climate and Food on Dominant Consumers and Their Consequences for Coastal Ecosystems

Abstract

This body of work explores dynamics of temperate marine grazers that are sensitive to food availability and inhabit regions with dramatic contemporary variation in abiotic conditions due to nearshore upwelling. Climate change projections indicate that such environmental fluctuation in these systems will increase in both intensity and variability in the coming decades. Chapter 1 focuses on the temperate red sea urchin Mesocentrotus franciscanus, which can denude highly productive kelp forests through their voracious grazing, often re- sulting in the formation of barren habitats which can persist for decades. In this chapter I first used respirometry to demonstrate how red sea urchins from wild populations depress their metabolism in barrens relative to kelp forests in the Pacific North West (PNW) [205]. Then I conducted a laboratory feeding experiment which provided evidence that metabolic depression and gonadal biomass reduction in red sea urchins are coupled with food deprivation, but that this response is highly plastic and reversible over 33 days and was not accompanied by differences in feeding rate or assimilation e fficiency. Additionally, Chapter 1 provides empirical validation for the use of fatty acid based dietary tracers for inferring algal diets in M. franciscanus. Chapter 2 builds upon these insights by applying the use of gonadal and fatty acid biomarkers in situ to trace the transfer of newly available algal food resources to key forest consumers, M. franciscanus and the endangered northern abalone, Haliotis kamtschatkana in the context of a collaborative ecological restoration project in Haida Gwaii, British Columbia, Canada. This chapter also includes the development of a granular library of kelp forest dietary resources based on multivariate fatty acid biomarker profiles. Chapter 3 investigates the impacts of contemporary ocean acidification and marine heatwaves on rates of herbivory and energetics in the dominant ecosystem engineer, Strongy-locentrotus purpuratus using a manipulative mesocosm experiment. Ecological consequences of food and climatic impacts on individual herbivory and energetics are discussed.