Science Serving Maryland's Coasts

R/SV-3

Resilience of Vallisneria americana in the Chesapeake Bay

Principal Investigator: 

Katharina A. M. Engelhardt

Start/End Year: 

2016 to 2018

Institution: 

Appalachian Laboratory, University of Maryland Center for Environmental Science

Co-Principal investigator: 

Maile C. Neel, University of Maryland, College Park, Department of Plant Science and Landscape Architecture

Strategic focus area: 

Resilient ecosystem processes and responses

Description: 

Past catastrophic declines of submersed aquatic vegetation (SAV) in the Chesapeake Bay (CB) have reduced habitat extent and compromised the ability of SAV beds to resist environmental change or recover after a disturbance. As a result, many SAV beds are small and ephemeral with diminished capacity to function as sediment filters, shoreline buffers, and habitat for fish and shellfish. The objective of this study is to contribute to management solutions that enhance the resilience of SAV beds in the CB. We argue that quantifying connectivity among SAV beds is a research priority because if informs managers as to spatial structure needed for disturbed SAV beds to be recolonized or rescued by seeds, turions or plants dispersing from other SAV beds. We further argue that connectivity among SAV beds enhances genetic and phenotypic diversity, which provides the raw material for acclimation and adaptation. In support of these arguments we plan to test three hypotheses that determine whether 1. connectivity drives persistence and rate of recovery; 2. connected patches are higher in genotypic diversity; and 3. genotypes differ in functional traits and plasticity. We propose to work with Vallisneria americana, a SAV species that is abundant in fresh and oligohaline portions of the CB and is a target of restoration. Prior research funded by Sea Grant has shown us that V. americana in the CB is not one panmictic population, rather genetic substructures exist. Experiments provided evidence that populations differ in genotypic and phenotypic diversity. We propose to expand on this knowledge with an exciting interdisciplinary research program that integrates a) spatial and temporal analysis of SAV bed persistence and connectivity using digital annual coverages of SAV; b) genetic variation in ~700 V. americana genotypes sampled across 3 focus areas - Susquehanna Flats and Fishing Battery, Elk River, and Central Bay and c) in-depth greenhouse experiments with 100 genetically identified genotypes that evaluate functional diversity within populations and determines how this diversity affects resilience through flower and turion production. Results of the proposed project will inform strategies for selecting donor beds and provide the information necessary for prioritizing management areas to maximize connectivity among SAV beds and ensure resilience. We will communicate our conclusions to managers and policy makers within the Chesapeake Bay community (Maryland Department of Natural Resources, the Chesapeake Bay Foundation, and the Chesapeake Bay Program) through presentations, an outreach brochure, a podcast, and informal information exchange. We further propose to organize a SESYNC working group that will bring together scientists and economists to synthesize knowledge of SAV resilience across species and locations. This working group will include and reach out to managers, policy makers, students, and teachers to broaden perspectives and provide educational opportunities. 

Impact/Outcome: 

Relevance: Bay grasses provide habitat for crabs and benthic organisms, as well as hiding places for larger fish trying to evade predators. The grasses help clean the water by slowing flows enough for sediment to settle to the bottom. For many decades, grass beds were greatly reduced or even eliminated from much of their historic range in the Chesapeake Bay, primarily due to poor water quality. When populations are so drastically reduced for so long a time, genetic diversity can be lost. Without genetic diversity, the grasses have limited potential for acclimation and adaptation to novel conditions. Natural resources managers have expended great effort for many years to plant new beds. But some of those beds did not thrive because of lack of light penetration, and possibly because of sensitivity to climate change, higher temperatures, or other factors.

Response: Wetland ecologist Katharina Engelhardt and botanist Maile Neel worked with several students on a Maryland Sea Grant funded project to examine Vallisneria americana grass beds in the Chesapeake and see how diverse they are genetically, how that impacts their growth, how connected the grass beds are, and how to replicate growth successes. In addition, the researchers were curious to see how plant diversity is distributed within and among sea grass populations. Determining if wild celery had limited genetic diversity in Bay grass beds is paramount to understanding the potential for future resilience. They also sought to determine if plants from different parts of the Bay grew better under their “home” conditions or if they could be planted more broadly without negative consequences.

Results: The team now has numerous genetic clones of the Vallisneria americana from the Chesapeake and can subject the different genotypes to varying conditions, including less light and higher temperatures. As they continue to develop this information and map out which beds are successful where, they can help inform decisions on where public entities should plant grasses and expand the success of sea grasses in the Bay.