Eelgrass restoration by seed maintains genetic diversity: case study from a coastal bay system (original) (raw)
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Eelgrass (Zostera marina) forms the foundation of an important shallow coastal community in protected estuaries and bays. Widespread population declines have stimulated restoration efforts, but these have often overlooked the importance of maintaining the evolutionary potential of restored populations by minimizing the reduction in genetic diversity that typically accompanies restoration. In an experiment simulating a small-scale restoration, we tested the effectiveness of a buoy-deployed seeding technique to maintain genetic diversity comparable to the seed source populations. Seeds from three extant source populations in San Francisco Bay were introduced into eighteen flow-through baywater mesocosms. Following seedling establishment, we used seven polymorphic microsatellite loci to compare genetic diversity indices from 128 shoots to those found in the source populations. Importantly, allelic richness and expected heterozygosity were not significantly reduced in the mesocosms, which also preserved the strong population differentiation present among source populations. However, the inbreeding coefficient F IS was elevated in two of the three sets of mesocosms when they were grouped according to their source population. This is probably a Wahlund effect from confining all half-siblings within each spathe to a single mesocosm, elevating F IS when the mesocosms were considered together. The conservation of most alleles and preservation of expected heterozygosity suggests that this seeding technique is an improvement over wholeshoot transplantation in the conservation of genetic diversity in eelgrass restoration efforts.
The population genetics of Morro Bay eelgrass (Zostera marina)
Seagrass populations are in decline worldwide. Zostera marina (eelgrass), one of California's native seagrasses, is no exception to this trend. In the last 8 years, Morro Bay, California has lost 95% of its eelgrass. Eelgrass is an ecosystem engineer, providing important ecosystem services such as sediment stabilization, nutrient cycling, and nursery habitats for fish. The failure of recent restoration efforts necessitates a better understanding of the causes of eelgrass decline in this estuary. Previous research on eelgrass in California has demonstrated a link between population genetic diversity and eelgrass bed health, ecosystem functioning, and resilience to disturbance and extreme climatic events. The genetic diversity and population structure of Morro Bay eelgrass populations has not been assessed until this study. Additionally, we compare Morro Bay eelgrass to Bodega Bay eelgrass in northern California. We conducted fragment length analysis of 9 microsatellite loci on 133 Morro Bay samples, and 20 Bodega Bay samples. We found no population differentiation within the bay, and no difference among samples growing at different tidal depths. Comparison with Bodega Bay in northern California revealed that Morro Bay eelgrass contains three first generation migrants from a northern eelgrass population, but remains considerably genetically differentiated. Despite the precipitous loss of eelgrass in Morro Bay between 2007 and 2017, genetic diversity remains comparable to other populations on the west coast.
Journal of …, 2012
The seagrass Zostera marina is widely distributed in coastal regions throughout much of the northern hemisphere, forms the foundation of an important ecological habitat, and is suffering population declines. Studies in the Atlantic and Pacific oceans indicate that the degree of population genetic differentiation is location dependent. San Francisco Bay, California, USA, is a high-current, high-wind environment where rafting of seed-bearing shoots has the potential to enhance genetic connectivity among Z. marina populations. We tested Z. marina from six locations, including one annual population, within the bay to assess population differentiation and to compare levels of within-population genetic diversity. Using 7 microsatellite loci, we found significant differentiation among all populations. The annual population had significantly higher clonal diversity than the others but showed no detectible differences in heterozygosity or allelic richness. There appears to be sufficient input of genetic variation through sexual reproduction or immigration into the perennial populations to prevent significant declines in the number and frequency of alleles. In additional depth comparisons, we found differentiation among deep and shallow portions in 1 of 3 beds evaluated. Genetic drift, sweepstakes recruitment, dispersal limitation, and possibly natural selection may have combined to produce genetic differentiation over a spatial scale of 3-30 km in Z. marina. This implies that the scale of genetic differentiation may be smaller than expected for seagrasses in other locations too. We suggest that populations in close proximity may not be interchangeable for use as restoration material.
Journal of Heredity, 2010
Zostera marina (eelgrass) can be found in the North Atlantic on the coast of Europe and on the east and west coasts of North America. Over the last 30 years, this once robust species has been reduced to sparse patchy populations due to disease and anthropogenic effects. In order to better understand the consequences of this devastation on the population genetics of the species, we have analyzed the population structure of western Atlantic Z. marina, employing microsatellite DNA polymorphisms. Although high fixation index values suggest moderate genetic differentiation among most of the Z. marina sites, population diversity was low. This lack of diversity was supported by a general dearth of observable heterozygotes in these sites; mean observed heterozygosity values (0.14-0.46) were lower than the mean expected heterozygosity values (0.57-0.81). Additionally, the mean F IS (coefficient of local inbreeding) values in these sites were positive, again indicating a surfeit of homozygotes. Allelic richness suggests that Chesapeake Bay has the greatest internal genetic diversity of the sites studied. Inbreeding seems prevalent in these American populations, suggesting possible reproductive fitness problems in the future. There is evidence of demographic bottlenecking and particularly low genetic diversity in Long Island. Northern Maine had the highest effective population size, suggesting a possible use in future restoration projects.
Estuaries and Coasts
Seagrass populations are in decline worldwide. Eelgrass (Zostera marina L.), one of California's native seagrasses, is no exception to this trend. In the last 8 years, the estuary in Morro Bay, California, has lost 95% of its eelgrass. Population bottlenecks like this one often result in severe reductions in genetic diversity; however, this is not always the case. The decline of eelgrass in Morro Bay provides an opportunity to better understand the effects of population decline on population genetics. Furthermore, the failure of recent restoration efforts necessitates a better understanding of the genetic underpinnings of the population. Previous research on eelgrass in California has demonstrated a link between population genetic diversity and eelgrass bed health, ecosystem functioning, and resilience to disturbance and extreme climatic events. The genetic diversity and population structure of Morro Bay eelgrass have not been assessed until this study. We also compare Morro Bay eelgrass to Bodega Bay eelgrass in Northern California. We conducted fragment length analysis of nine microsatellite loci on 133 Morro Bay samples, and 20 Bodega Bay samples. We found no population differentiation between the remaining beds in Morro Bay and no difference among samples growing at different tidal depths. Comparisons with Bodega Bay revealed that Morro Bay eelgrass contains three first-generation migrants from the north, but Morro Bay remains considerably genetically differentiated from Bodega Bay. Despite the precipitous loss of eelgrass in Morro Bay between 2008 and 2017, genetic diversity remains relatively high and comparable to other populations on the west coast.
Population Ecology, 2013
Within Barnegat Bay, New Jersey, eelgrass (Zostera marina) populations have declined by 62 % over the last 20 years. To better understand the consequences of this devastation, we have previously employed microsatellite DNA polymorphisms to analyze the population structure of Z. marina within Barnegat Bay, as well as along the eastern United States seaboard. We have restored populations of Z. marina in Barnegat Bay over the last 10 years to help assess the best planting conditions and ecotypes that might be used in long-term restoration strategies. In this study, we examined the genetic health of the restored populations compared to that of the donor eelgrass populations within the bay. Using microsatellites, we can identify which parental founding ecotypes survived the restoration process over multiple generations. The frequency of observed heterozygotes, although higher than in the natural populations, still indicates reduced levels of diversity and connectivity. The inbreeding frequency is high in the restored populations, but lower than what is seen in the native populations. All restored populations have effective population values [50, suggesting a high probability of survival in the short term.
Marine Biology, 2011
Massive losses of eelgrass Zostera marina beds in Japan have occurred over the past 100 years. Toward their restoration, transplantation of eelgrass has been attempted in some areas, including Tokyo Bay. This study examined population genetic structures and gene flow in eelgrass in Tokyo Bay to establish guidelines for conducting restoration. Genotypes of a total of 360 individuals from 12 beds were determined using five microsatellite markers. The eelgrass beds in inner bay had above-average genetic diversity. A neighbor-joining tree based on F ST values among beds revealed that a strong gene flow had occurred among six beds in the inner bay. Genetic assignment testing of drifting shoots indicated that those with seeds migrate in both directions between the inner and outer bay. We suggested that the restoration of eelgrass in the innermost part of Tokyo Bay, where natural habitats have been lost, should be conducted using the inner bay beds.
Estuaries, 1998
The objective of this studywas to gain baseline population data on the genetic diversity and differentiation of eelgrass (Zostera mar/na L.) populations in the Chesapeake and Chincoteague bays. Natural and transplanted eelgrass beds were compared using starch gel electrophoresis of allozymes. Transplanted eelgrass beds were not reduced in genetic diversity compared with natural beds. Inbreeding coefficients (Fis) indicated that transplanted eelgrass beds had theoretically higher levels of outcrossing than natural beds, suggesting the significance of use of seeds as donor material and of seedling recruitment following transplantation diebacks. Natural populations exhibited very great genetic structure (FsT = 0.335), but transplanted beds were genetically similar to the donor bed and each other. Genetic diversity was lowest in Chincoteague Bay, reflecting recent restoration history since the 1930s wasting disease and geographical isolation from other east coast populations. These data provide a basis for developing a management plan for conserving eelgrass genetic diversity in the Chesapeake Bay and for guiding estuary-wide restoration efforts. It will be important to recognize that the natural genetic diversity of eelgrass in the estuary is distributed among various populations and is not well represented by single populations. 9 1998 Estuadne Research Federation
Fine-scale genetic structure and relatedness in the eelgrass Zostera marina
The genetic composition of groups of individuals can significantly influence the productivity, resilience, and functioning of communities and ecosystems. For example, the relatedness of individuals within a group often dictates whether their interactions are competitive or cooperative. It is therefore necessary to characterize the genetic structure of populations at spatial scales relevant to these interactions and to determine the distribution of genetic diversity at those scales. Using microsatellite data, we assessed fine-scale population structure of Zostera marina, an important habitat-forming seagrass, within and between Bodega Harbor and Tomales Bay in northern California, USA. Despite the potential for long-range dispersal, we found significant population structure at all hierarchical scales (among bays, among sites, among tidal heights), corresponding to distances ranging from meters to tens of kilometers. The pattern of genetic differentiation that emerged at local scales differed between bays, with Tomales Bay being more structured even though the Euclidean distances among sites were similar in each bay. The relatedness of genets within a tidal height also differed among bays: in Bodega Harbor most genets occurred in proximity to unrelated individuals, whereas in Tomales Bay, genets were mixed with their close relatives, likely due to decreased dispersal. These contrasting kin structures, coupled with highly variable levels of clonal diversity, underscore the importance of examining variation at multiple scales, as this reveals genetic factors which might play an important role in many ecological processes.
Genetic structure of eelgrass Zostera marina meadows in an embayment with restricted water flow
2006
ABSTRACT: Genetic structure of the seagrass Zostera marina in a coastal lagoon with restricted water flow, and with heterogeneous water residence times and oceanographic characteristics, was assessed using 8 polymorphic microsatellite loci. Analyses of genetic differentiation (θ) and Bayesian clustering suggested that the Z. marina population in San Quintin Bay (SQB) is genetically substructured, with at least 4 genetically different groups:(1) West Head,(2) Mouth,(3) East Arm, and (4) East Head.