The Vallisneria Genetics Project
Effects of Genetic  Diversity on Restoration Success

Project Description

Our Team

Funders & Collaborators

Progress & Discoveries

Publications & Presentations

Management Workshop

Engelhardt Home

Project Description:

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 prevalent 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. SAV cover has increased substantially in recent years but is still only a fraction of the 80,000 hectares that are estimated to have existed before Hurricane Agnes in 1972 (see right; data from Virginia Institute of Marine Science). 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.

Background:

When degraded areas are restored, they should 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.  Recent modeling efforts indicate that genotypic diversity within species allows individuals to occupy different niches and promotes species coexistence and thus community diversity (Vellend 2006).  These modeling results are supported by empirical evidence that genotypes of Zostera marina showed differential resistance to herbivory by geese (Hughes & Stachowicz 2004) and V. americana genotypes have differential tolerance of pollutants (Biernacki & Lovett-Doust 1997). 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 environments.

We focus on V. 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.

Predictions:

Without considering genetic diversity when selecting restoration stock, a nursery may mass-produce one or a few clones from one site that are then used to restore areas throughout the Bay. This may cause restoration efforts to fail if that clone is not adapted to grow at many of the planting sites.  Even if restoration is successful in the short-term, environmental fluctuations or directional change may cause all restored populations to catastrophically fail if populations cannot adapt to the new conditions. Taking these issues into consideration, we predict that genetic diversity plays a role in the chances of restoration success. Specifically we predict that 1) individuals with higher levels of heterozygosity will have higher rates of survival and growth than highly homozygous individuals;  2) genotypically diverse plantings will have higher survival and growth rates than monotypic stands; and 3) propagules that are collected close to the planting sites will have higher survival and growth rates than propagules collected from more distant locations.  Testing these predictions will allow us to make recommendations to restoration agencies managing natural resources in the Chesapeake Bay, and in coastal ecosystems in general, how and when it is important to consider to genetic diversity when restoring SAV beds.

Biernacki, M., and J. Lovett-Doust. 1997. Vallisneria americana (Hydrocharitaceae) as a biomonitor of aquatic ecosystems: Comparison of cloned genotypes. American Journal of Botany 84:1743-1751.

Hughes, A. R., and J. J. Stachowicz. 2004. Genetic diversity enhances the resistance of a seagrass ecosystem to disturbance. Proceedings of the National Academy of Sciences of the United States of America 101:8998-9002.

Vellend, M. 2006. The consequences of genetic diversity in competitive communities. Ecology 87:304-311.