Research
Salt marshes in the southeastern US are dominated in the low and mid intertidal by the clonal foundation plant, Spartina alterniflora. From first glance a marsh appears as a single clonal stand of grass; yet, Spartina exhibits high levels of genetic and phenotypic variation across small spatial scales within natural marshes. I am interested in understanding the evolutionary underpinning and ecological consequences of Spartina intraspecific (within-species) variation within marsh communities. My current research focuses on:
Causes & Consequences of Intraspecific Variation
Adaptation in Spartina across tidal elevation:
Salt marshes form across a natural stress gradient in salinity and inundation along tidal elevation. Spartina is typically characterized by two distinct phenotypes: tall-form (1-2m) plants at lower tidal elevations and short-form (<0.5m) plants at higher tidal elevations along the US Atlantic coast; yet whether this trait variation reflected plastic and/or genetically differentiated responses to these environmental conditions remained unclear. Combining common garden and reciprocal transplant experiments, with genomic analyses of natural populations, we showed repeated genetic differentiation between tall- and short-form Spartina across their geographic distribution, as well as adaptation in two ecologically-important traits (stem height and biomass allocation) across tidal elevation. This observed genetic differentiation in Spartina likely underpins marsh health and functioning, and provides an under appreciated mechanism that might increase capacity of marshes to adapt to rising sea levels (Zerebecki et al. 2021).
Influence of within-species variation on species interactions:
Competition and herbivory are two processes that shape distribution and production of Spartina. To examine how these species interactions varied with Spartina genotype, we manipulated Spartina genotypic identity, neighbour identity (needlerush, Juncus roemerianus), and consumer pressure (periwinkle snail, Littoraria irrorata) in a year long field experiment. We found independent effects of all 3 factors on this plant-plant-herbivore interaction. Further, using a common garden experiment, we were able to show that Spartina genotypes vary in morphological, phenological and palatability traits and then test whether these genotypic-specific trait differences were related to variation in field performance. We found that Spartina genotypes that had higher reproductive output were more negatively affected by snails, and moreover, Spartina genotype-specific traits influenced both snail behaviour and plant neighbour height (Zerebecki et al. 2017).
As mangroves encroach into Spartina-dominated marshes, we are currently investigating the role of size-variation within the black mangrove (Avicennia germinans) on this plant-plant-herbivore interaction using a combination of surveys, tethering and exclusion field experiments.
Ecological Effects of Diversity
Biodiversity (including genes, functional traits, and species) can influence the structure and function of ecosystems. My research explores the ecological effect of genetic and taxonomic diversity on coastal marine ecosystems.
Diversity effects across environmental gradients
Previous studies have illustrated that plant genetic diversity can positively affect plant production and the community of associated species; yet there is limited understanding of how these effects may vary across different environmental conditions. Using a multiple year experiment, we manipulated Spartina diversity and nutrient availability across tidal elevation to examine how diversity impacts plant production and the associated invertebrate community and whether this diversity effect changes across environments. We found that under most environments tested, Spartina genotypic diversity had a positive effect on population and community responses (Zerebecki & Hughes Journal of Ecology in press).
Diversity-stability in coastal ecosystems
Biodiversity can also enhance the resilience of ecosystems to disturbance. As a graduate student and post-doctoral scholar, I was part of the Alabama Center for Ecological Resilience (ACER) consortium based at Dauphin Island Sea Lab that examined the influence of biodiversity on the response of coastal ecosystems to the Deepwater Horizon oil spill. Within coastal wetlands, we assessed whether taxonomic and genetic diversity could increase plant resilience in response to oil disturbance using both lab experiments and field surveys (Hughes et al. 2018, Zerebecki et al. 2021). Further, I am lead a synthesis of ACER mesocosm experiments across coastal ecosystems and found that diversity can reduce the negative impacts of oiling, but the magnitude depends on both the response measured (i.e., evident for within-in trophic level responses) and type of diversity present (i.e., greater for taxonomic than genetic; Zerebecki et al. 2022).
Environmental Impacts on Coastal Ecosystems
Given that global climate change is one of the major threats to biodiversity, understanding how environmental changes may impact coastal ecosystems is embedded in much of my research.
Sea-level rise in Marshes
Restoration and resilience of marshes to sea-level rise requires a better understanding of how adapted plants are to their current conditions. Spartina structural traits such as stem height and biomass allocation are key drivers of marsh sediment accumulation rates and thus predicted to influence the maintenance of the marsh platform. However, as our findings of local adaptation between tall- and short-form Spartina (see above) suggest, it may be critically important to understand how genetic- and environmentally-mediated trait variation may influence the response of marshes to sea level rise.
Tropicalization of Temperate Marshes
Warmer winter temperatures in the Gulf of Mexico have facilitated the expansion of the black mangrove (Avicennia germinans) into marshes typically dominated by Spartina. We are conducting field surveys and experiments to understand the impact that this change in plant composition will have on the plant and associated animal community (e.g., Zerebecki et al. 2021).
Disturbance
Disturbance can shape local species composition and abundance and thus, understanding the impact of both human-induced and natural disturbances on wetlands is critically important.
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Oil Exposure: As part of the ACER consortium, I have been investigating the impacts of the Deepwater Horizon oil spill on nearshore marine ecosystems.
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Wrack: Naturally, seagrass sloughs off its leaves and they are carried by tides and deposited into the marsh as wrack. I am exploring how this physical disturbance influences plant interactions in the marsh.
Increased Temperature impacts on Marine Communities
Climate-change associated temperature increase can have wide-ranging impact on species abundances, distributions and interactions. For my Master's thesis, I examined lethal temperature tolerance (LT50) and heat shock protein expression of native and invasive fouling community species (i.e. tunicates and bryozoans) in California. Invasive species had higher temperature tolerances than native species and thus, more likely to be favored under climate change predictions which may have ecological impacts (e.g., species composition shifts) in these communities (Sorte, Williams & Zerebecki 2010, Zerebecki & Sorte 2011). Since then, I have collaborated on a meta-analysis to examine intrinsic and extrinsic factors that may predict the thermal sensitivity of marine populations to temperature increases (Hughes et al. 2019).
