Human-induced changes in the world’s natural ecosystems have caused unprecedented declines in species and genetic diversity, leading to declines in ecosystem health, including their capacity to cope with environmental fluctuations. Such declines are especially common in estuaries such as the Chesapeake Bay, where reductions of submersed aquatic vegetation (SAV) abundance have both been caused by and led to declines in water quality and associated fisheries. Coverage of SAV is believed to have been above 80,000 hectares before Hurricane Agnes in 1972. In recent years, SAV in the Bay has fluctuated between 25,000 and 40,000 hectares.
The far-reaching consequences of SAV decline have focused attention on effective ways of restoring the Bay’s living resources. Resulting restoration efforts of SAV in the Chesapeake Bay have been impressive; however, success has been undeniably mixed and is leading us to ask what role genetic diversity and sources of restoration stock may have in enhancing restoration success and long-term health of the Bay’s resources.
When degraded areas are restored, they need to contain an adequate species complement to withstand environmental fluctuations. All available evidence indicates that it is equally important to preserve genetic diversity within species in conservation and restoration efforts. Our project explores three levels of genetic diversity that may be important in conferring a greater chance that a restoration effort will be successful: levels of inbreeding within individuals, levels of diversity among individuals (e.g., numbers of alleles, genotypes, and phenotypes), and the adaptation of individuals to local environment.
We focus on Vallisneria americana because it was once a dominant species in the Chesapeake Bay, it is considered an important food resource for wildfowl, it does not interfere with recreational uses of waterways, and it is used in restoring freshwater portions of the Bay by a variety of groups. As with many aquatic species, V. americana is a dioecious submersed aquatic macrophyte that is capable of both clonal growth and sexual reproduction with vegetative expansion often being the dominant form of propagation. It is not known how past population bottlenecks and restoration activities may have affected the natural genetic diversity of freshwater SAV growing in the Chesapeake Bay. However, this information is needed to effectively monitor the health of this important living resource which is not stable from year to year and can conceivably re-enter a period of decline if environmental conditions worsen due to unforeseen weather events. The amount and structure of genetic diversity within and among populations of V. americana in the Chesapeake Bay will depend on a combination of relative amounts of vegetative versus sexual reproduction, patterns of seed dispersal, nature of a seed bank, and population history.
We have collected over 550 individuals from 22 populations (14 natural color coded blue, 6 restored color coded red, 3 cultured) throughout the Chesapeake Bay region. Some natural and restored populations are paired to allow comparisons of genetic diversity while controlling for differences in environmental conditions as much as possible. Collection sites represent much of the geographic extent of V. americana in the Bay to encompass a number of environmental gradients, such as salinity, temperature, nutrient regime, and depth.
Shoot tissue for genetic analysis was removed from each ramet and transported to College Park for further processing. We purchased a microsatellite library for V. americana from the company Genetic Services Incorporated. Lab work focuses on screening 54 potential repeat loci to determine 1) if they can be amplified with high specificity and repeatability, 2) if the amplified fragment actually contains the desired repeat, and 3) if they are polymorphic across individuals and sites. We test for polymorphism using a set of eight individuals from four locations. We currently have four loci we have successfully taken through all these steps.
Whole plants were transported to the Appalachian Laboratory’s greenhouse where they were planted in individual 2.5 quart plastic containers containing a generic brand topsoil topped with silica sand. Water was added slowly in the form of a fine mist. The growing conditions within the greenhouse are kept at moderate levels, with no temperature extremes. A light filtering shade is drawn over the samples to prevent chlorophyll bleaching. The greenhouse is watered by an automated misting system to ensure that each pot is filled to capacity.
We are also micropropagating V. americana in the laboratory using a variety of micropropagation techniques. We have the capacity to propagate 400 individuals in 50mm test tubes and 250 individuals in mason jars.