Research in our lab concerns the ecological causes of patterns of biodiversity, and the consequences of variation in diversity for populations, communities and ecosystems. The vast diversity of life forms in the marine environment (many of the animal phyla are exclusively marine, or nearly so) makes it a rewarding system for addressing these sorts of issues. We study organisms from all over the tree of life, including vascular plants, algae (seaweed), bacteria, and a range of invertebrate taxa including corals, hydroids, crabs, echinoderms, polychaetes, ascidians, bryozoans, and gastropods.
The main projects in the lab currently include:
- Maintenance and functional role of species diversity in rocky intertidal communities
- The ecological consequences of genetic vs phenotypic diversity
- Community assembly in marine invertebrates
- Biogeographic patterns of community organization (Zostera Experimental Network)
- Marine plant microbiomes
We also have a long standing interest in a number of other areas, including:
Much of our local field work occurs in the area of Bodega and Tomales Bays (below), but we work collaboratively elsewhere in California and around the world.
Effects of species diversity on communities and ecosystems
While the relationship between species diversity and community stability has long been a topic of theoretical interest to ecologists, recent concern about the loss of biodiversity has prompted renewed interested in what the consequences of diversity loss might really be. We have worked on three fronts in this research area: documenting patterns of change in biodiversity in real systems, performing experiments to demonstrate the mechanisms by which diversity does and does not affect communities and ecosystems, and collaborating with other ecologists, conservation biologists and economists to test links between the loss of biodiversity and the provision of goods and services to humans by natural ecosystems. Current experimental work in this area focuses on rocky shore seaweed and invertebrate communities, testing the relative influence of diversity vs. other drivers of community structure and function; the role of environmental heterogeneity in both promoting diversity and driving the effects of diversity, and the degree to which recovery of communities is stochastic vs deterministic.
Some communities, such as coral reefs, kelp forests, and seagrass beds are comprised of a single dominant species, and genetic diversity within these species may play an analogous role to species diversity in more speciose systems. Through manipulative field experiments and laboratory mesocosms, we have been examining the effects of genetic diversity in the eelgrass Zostera marina on community function and stability. Field experiments show that genetic diversity enhances community resistance to natural disturbances by grazing geese and algal bloom as well as experimentally imposed disturbances. These differences in disturbance response affect the abundance of epifaunal grazers such as amphipods and other small crustaceans on seagrasses. Our current efforts in this area examine whether relatedness among genotypes predicts their ecological differentiation, and whether traits or genetic differences better predict the outcome of intraspecific interactions, community productivity, and ecosystem functioning.
Community Assembly in Marine Invertebrates
The study of community assembly processes currently involves (a) long standing questions about the relative importance of environmental filtering vs. niche partitioning in a wide range of ecosystems, and (b) more recent questions about methodology. The basic problem arises when a number of apparently quite similar species co-occur in a single place over the long run leading to questions about what differences among the species prevent competitive exclusion. We have examined these questions both in sessile marine invertebrate (fouling) communities, dominated by solitary and colonial ascidians all of which compete for space as a limiting resource and more recently in amphipods and isopods living on seagrasses and associated seaweeds. Both of these systems have the advantage that both experimental and observational / comparative approaches can be used in complementary ways to address these questions. We use both traditional “trait based” approaches as well as phylogenetic methods and mathematical models to assess the importance of ecological and evolutionary differences (vs. stochastic processes) in determining the coexistence of species in communities.
Local scale studies of community structure conducted in different regions often conflict, leading to considerable debate about the major forces driving community structure. Differences in methodology among research groups are often confounded with these among-site differences, making generalization difficult. This is the case in seagrass beds, which are often in decline due to overgrowth by epiphytic and macro algae. The cause of this overgrowth is in dispute: there is evidence for both excess nutrients and reduced consumption by grazers as the primary causes. Other studies implicate the importance of biodiversity: both of the grazers and of the grass itself in determining seagrass bed health. Together with the labs of Emmett Duffy and Kevin Hovel, we have initiated a network of over 20 research groups worldwide (Zostera Experimental Network, ZEN) to examine the forces responsible for ecosystem structure and function in beds of the eelgrass, Zostera marina. These efforts included a global distributed experiment testing the relative importance of top down vs. bottom up forces, direct tests of the relative strength of predation on grazers, as well as in depth survey of the grazer community and genetic composition of the beds.
Time Lapse Video of ZEN Sampling at Sacramento Landing, Tomales Bay California, September 2014
We are interested in integrating the long interest in seagrass ecology and ecosystem science with more recent work in microbiology to produce a deeper, more mechanistic understanding of the ecology and evolution of seagrasses and the coastal ecosystems which depend on them. Much of this work is done in collaboration with Jonathan Eisen. The main thrusts of this work include both ecological and evolutionary questions: How have the microbial communities associated with seagrasses coevolved with their hosts and what roles, in the past and currently, do microbes play in adaptations of plants to the marine environment? What controls the community assembly of the microbiome of Zostera marina, a model seagrass species? What role does the microbial community play in the functional ecology of Zostera marina, especially with respect to sulfur and nitrogen metabolism?
The first phase of this project is focused on the collection of microbes associated with eelgrass, Zostera marina from throughout the geographic range of Zostera. In a recent paper, we found that that the leaf microbiome is quite variable and overall scarcely distinguishable from the microbes in the surrounding water, whereas root microbiomes are similar across geographic scales and quite distinct from sediment micro biomes. Specifically, roots appear to be enriched in microbes from groups associated with sulfur metabolism. In progress work also assesses how the micro biome is affected by (and affects) eelgrass response to heat waves, local adaptation of eelgrass to environmental conditions, and eelgrass wasting disease. A recently funded project specifically targets the response of the micro biome to wasting disease and the role that microbes might play in facilitating or impeding wasting disease and corresponding seagrass decline. We are currently searching for a postdoc to assist with this work.
Decorator crabs are a diverse group of brachyuran crabs within the superfamily Majoidea that have the unusual habit of “decorating” their carapace with bits of algae and invertebrates. They accomplish this by attaching these materials to specialized hooked setae on their carapace that hold decorations in place much in the same way that Velcro latches onto fabric. We study the fascinating natural history of these crabs and use phylogenetic methods to examine what these crabs can tell us about the ecology and evolution of antipredator behaviors in general. These crabs and our work on them was featured on the ABC evening news on Halloween in a piece on animals that “dress up for Halloween”. You can watch this video here
Ecological investigations have long focused on negative interactions (competition and predation) and how they affect population and community structure. Although positive interactions (interactions in which one at least one species benefits and neither is harmed were studied decades ago, there has been limited effort to factor them into our models or thinking about factors impacting populations and communities. Ongoing work in our lab tries to balance this by using experimental investigations of positive interactions to study the population biology of the participants and the effects of these interactions on communities as a whole. Our most recent work focuses on the role of multiple mutualists in the outcome of host-mutualist interactions.
Introduction of species to new biogeographic regions poses both challenges for conservation of native communities and opportunities for increasing our ecological understanding of the forces governing the assembly, structure and functioning of these communities. Work in our lab on invasions focuses on aspects of communities that either promote or retard the success of invasive species. Much of this work has involved either the effects of native diversity on invasion resistance or the effects of climate change on the relative success of native vs. exotic species. Recent work focuses on the processes promoting coexistence of natives and exotic species, and the relative role of native vs exotic suspension feeding invertebrates on water clarity through its effects on phytoplankton abundance and community composition.