Patterns and consequences of changing biodiversity in coastal marine food webs
The growing realization that man is driving species extinct across the globe has brought about a renaissance in the study of how biodiversity influences the functioning of ecosystems. Much of this work has centered on terrestrial plants, and may or may not be reflective of changes in the marine realm. Within the oceans, marine ecosystems are being altered by overfishing, urbanization, habitat degradation, climate change, and more. At the same time, at local spatial scales, species invasions due to increased global commerce and aquaculture have often outpaced extinctions. Here, I ask, how are the dual processes of extinction and invasion altering the diversity and structure of food webs in the oceans, and what are the consequences?
Using published species lists, I find that most marine species going extinct either locally or globally either top and secondary predators, while most exotic species are primary consumers towards the base of food webs (Chapter 1). To examine the consequences of these changes in trophic skew, I first look at how trophic cascades in California kelp forests are altered by losses in predator diversity (Chapter 2). I find that, around the California Channel Islands, sites with higher predator diversity have fewer herbivores and more kelp. In experiments with kelp forest mesocosms, I show a positive correlation between predator diversity and reduction in kelp consumption, in part due to different predators altering the behavior of different prey to reduce their consumption of kelp. Similarly, I show that top down control of sessile filter feeders in docks and marinas is decreased when predator diversity is lost (Chapter 3). Using a combination additive-replacement design and accompanying it with a meta-analysis of other combination experiments, I show that low predator diversity tends to be associated with stronger intraspecific interactions, a higher probability of having a resistant prey item, and a lower probability of including a strong consuming species, all potentially decreasing top down control of prey. Lastly, I show that increases in exotic sessile filter feeder diversity on docks can alter water filtration and nutrient production over long, but not short, temporal scales (Chapter 4).
0792: Aquatic sciences