Causes and Consequences of Kelp Forest Foundation Species Loss

With increasing biodiversity loss occurring worldwide, there is a need to understand how these losses will affect ecosystem structure and function. Certain species have a greater impact on the structure and function of ecosystems (i.e. foundation species, keystone species, ecosystem engineers) and therefore their importance suggests a need for understanding their dynamics. I focused on foundation species, which are those that provide the primary habitat and define the communities and ecosystems they create (Dayton 1972, Graham et al. 2007). My dissertation explores different causes and the cascading consequences of kelp forest foundation species loss. In chapter 1, I focus on the consequences of kelp forest biodiversity loss. The loss of the structure and energy that kelps provide leads to changes in species interactions, specifically the trophic complexity of food webs, however how these changes manifest is undescribed (Graham 2004). Sampling the stable isotopes of producer and consumer communities when kelp and other macroalgae are present, versus absent, while comparing these to naturally occurring consumer communities with low biodiversity, has revealed how overall biodiversity loss affects the complexity of food webs. I determined that the reductions in the diversity of kelp forest consumer food resources leads to reductions in the diversity of consumer trophic levels. This comes about through the reduction in food diversity for omnivores and herbivores which propagates to consumers at higher trophic levels. These findings suggest that more intact and biodiverse communities support greater food diversity and trophic complexity.