My research interests primarily focus on the ecology of marine systems, particularly the population and community dynamics of marine and coastal organisms in response to environmental stress and disturbance. Currently, I am studying the trophic and non-trophic impacts of habitat modifiers on foundational plant species within California salt marshes. My research seeks to improve ecological understanding of the drivers of salt marsh community structure, and how these may change across latitudinal gradients.
Animals influence community structure and ecosystem function via trophic interactions, however animals can also impact communities through non-trophic pathways, such as ecosystem engineering via burrowing. In salt marshes, for example, crabs can burrow into soils surrounding marsh vegetation and thereby alleviate hypoxic stress for plants. The activities of such organisms may mitigate the impacts of climate change by reducing environmental stress that would otherwise change plant communities. Importantly, such stress reductions could shift plant-plant interactions towards more negative, competitive interactions. The central goal of this research is to address how animals can influence community dynamics by modifying plant interactions via non-feeding pathways in Pacific coast salt marshes. I am conducting multi-factorial, manipulative caging experiments at four salt marshes - two southern California sites and two northern California sites – in order to examine how burrowing crabs impact the community composition of two dominant salt marsh plants, Spartina foliosa (Pacific cordgrass) and Sarcocornia pacifica (pickleweed). Identifying factors that mitigate stress will enhance our appreciation for the resilience of these ecosystems in the face of climate change. These results will also increase our understanding of the non-trophic effects of animals on community dynamics across varying abiotic conditions.
Crab Herbivory and Plant Palatability
In coastal salt marshes, crab herbivory can play a major role in influencing plant productivity and plant species zonation. Herbivore feeding preferences can depend on the palatability of plants and plant traits, where latitudinal variation can exist, with more intense herbivory and better developed prey defenses often occurring at low latitudes compared to high latitudes. Herbivore feeding preferences and plant palatability may vary along the California coast due to an abiotic stress gradient. The central goal of this research is to identify feeding preferences of herbivorous crabs in northern and southern California salt marshes in order to better understand patterns of local and regional community structure. Using feeding experiments, we will determine 1) the feeding preferences of the lined-shore crab, Pachygrapsus crassipes, along the California coast, and 2) plant palatability between regions. Identifying geographic variation in herbivore pressure will help our predictions for the resilience of these ecosystems in the face of climate change, as increased drought and salinity may intensify herbivory.
Although plant-plant interactions have been well-defined in Atlantic coast and Gulf coast salt marshes, we know considerably less about interactions between the dominant plant species in southern California. Additionally, the interactions between these dominant species (i.e. Spartina foliosa and Sarcocornia pacifica) are likely impacted by changes in soil salinity and precipitation regimes associated with El Niño. Here, we have designed a multi-year study to assess the interactions between S. foliosa and S. pacifica at two sites within San Diego, and how these interactions may be mediated by soil properties. This is a collaborative project with Jeremy Long, David Lipson, and Shelby Rinehart at San Diego State University.
Genetic Diversity and Spatial Structure of Cordgrass
Spartina alterniflora, salt marsh cordgrass, is the dominant plant in coastal wetlands along the North American Atlantic coast. Ecological disturbances in salt marshes, such as coverage by wrack, disease, and eat-outs, affects Spartina marshes from the Gulf of Mexico to New England and may reduce the diversity of S. alterniflora clones within a population or alter other genetic characteristics of a population by eliminating some genotypes. Nine polymorphic microsatellite loci were used to quantify the genetic characteristics (e.g., allelic richness, diversity, polyploidy, fixation index) of S. alterniflora populations at five salt marshes, as well as, to measure the spatial structure (size and shape of clones) of a single population in Upper Phillips Creek marsh (UPC). Over 250 individual plant samples were collected at three spatial scales. At UPC marsh, over 53 unique genotypes were found corresponding to a high clonal diversity index of 0.944, even when there is little evident phenotypic diversity. Although spatially separated by as much as 1, 15, 20, and 35 km, the five marshes were genetically connected as indicated by percent similarity calculations based on genetic similarity and geographic location. High clonal diversity indices and the abundance of genotypes indicate that sexual reproduction is important in the growth and expansion of S. alterniflora in these salt marshes. We hypothesize that disturbance may create ‘windows of opportunity,’ which favor seedling development and highly intermingled spatial arrangement of clones. The high clonal diversity found and the large number of multilocus genotypes indicated that sexual reproduction and seedling recruitment are underappreciated processes that may contribute to marsh resilience and resistance to disturbance and climate change.