About this dataset

Context

The dataset tabulates the San Francisco population over the last 20 plus years. It lists the population for each year, along with the year on year change in population, as well as the change in percentage terms for each year. The dataset can be utilized to understand the population change of San Francisco across the last two decades. For example, using this dataset, we can identify if the population is declining or increasing. If there is a change, when the population peaked, or if it is still growing and has not reached its peak. We can also compare the trend with the overall trend of United States population over the same period of time.

Key observations

In 2023, the population of San Francisco was 808,988, a 0.15% increase year-by-year from 2022. Previously, in 2022, San Francisco population was 807,774, a decline of 0.51% compared to a population of 811,935 in 2021. Over the last 20 plus years, between 2000 and 2023, population of San Francisco increased by 31,648. In this period, the peak population was 879,676 in the year 2018. The numbers suggest that the population has already reached its peak and is showing a trend of decline. Source: U.S. Census Bureau Population Estimates Program (PEP).

Content

When available, the data consists of estimates from the U.S. Census Bureau Population Estimates Program (PEP).

Data Coverage:

• From 2000 to 2023

Variables / Data Columns

• Year: This column displays the data year (Measured annually and for years 2000 to 2023)
• Population: The population for the specific year for the San Francisco is shown in this column.
• Year on Year Change: This column displays the change in San Francisco population for each year compared to the previous year.
• Change in Percent: This column displays the year on year change as a percentage. Please note that the sum of all percentages may not equal one due to rounding of values.

Good to know

Margin of Error

Data in the dataset are based on the estimates and are subject to sampling variability and thus a margin of error. Neilsberg Research recommends using caution when presening these estimates in your research.

Custom data

If you do need custom data for any of your research project, report or presentation, you can contact our research staff at research@neilsberg.com for a feasibility of a custom tabulation on a fee-for-service basis.

Inspiration

Neilsberg Research Team curates, analyze and publishes demographics and economic data from a variety of public and proprietary sources, each of which often includes multiple surveys and programs. The large majority of Neilsberg Research aggregated datasets and insights is made available for free download at https://www.neilsberg.com/research/.

Recommended for further research

This dataset is a part of the main dataset for San Francisco Population by Year. You can refer the same here

Population growth drives increasing demand for housing, jobs, food, education, transportation and many services. Population decline is the flip side of that dynamic, creating its own pressures on local business, government, housing and people.This map shows which areas are under significant pressure from population growth or decline. As the population of the U.S. continues to grow, the cities and the suburbs are experiencing changes in their population density. This map shows areas of declining density in brown, and high growth in dark green.Red areas will lose population by 2015, while green areas will grow. Darker green areas will grow more than 1.25% per year. Click on the map for details about an area. Use this map as a backdrop for your organization's locations, services areas, or other subjects. There is also a simple app showing this web map.You candownload the data from this map package.

Chart and table of population level and growth rate for the San Francisco metro area from 1950 to 2025.

About this dataset

Context

The dataset tabulates the South San Francisco population over the last 20 plus years. It lists the population for each year, along with the year on year change in population, as well as the change in percentage terms for each year. The dataset can be utilized to understand the population change of South San Francisco across the last two decades. For example, using this dataset, we can identify if the population is declining or increasing. If there is a change, when the population peaked, or if it is still growing and has not reached its peak. We can also compare the trend with the overall trend of United States population over the same period of time.

Key observations

In 2022, the population of South San Francisco was 63,484, a 1.36% decrease year-by-year from 2021. Previously, in 2021, South San Francisco population was 64,361, a decline of 2.67% compared to a population of 66,124 in 2020. Over the last 20 plus years, between 2000 and 2022, population of South San Francisco increased by 2,841. In this period, the peak population was 67,147 in the year 2016. The numbers suggest that the population has already reached its peak and is showing a trend of decline. Source: U.S. Census Bureau Population Estimates Program (PEP).

Content

When available, the data consists of estimates from the U.S. Census Bureau Population Estimates Program (PEP).

Data Coverage:

• From 2000 to 2022

Variables / Data Columns

• Year: This column displays the data year (Measured annually and for years 2000 to 2022)
• Population: The population for the specific year for the South San Francisco is shown in this column.
• Year on Year Change: This column displays the change in South San Francisco population for each year compared to the previous year.
• Change in Percent: This column displays the year on year change as a percentage. Please note that the sum of all percentages may not equal one due to rounding of values.

Good to know

Margin of Error

Data in the dataset are based on the estimates and are subject to sampling variability and thus a margin of error. Neilsberg Research recommends using caution when presening these estimates in your research.

Custom data

If you do need custom data for any of your research project, report or presentation, you can contact our research staff at research@neilsberg.com for a feasibility of a custom tabulation on a fee-for-service basis.

Inspiration

Neilsberg Research Team curates, analyze and publishes demographics and economic data from a variety of public and proprietary sources, each of which often includes multiple surveys and programs. The large majority of Neilsberg Research aggregated datasets and insights is made available for free download at https://www.neilsberg.com/research/.

Recommended for further research

This dataset is a part of the main dataset for South San Francisco Population by Year. You can refer the same here

This feature layer contains census tracts for the San Francisco Bay Region for Census 2020. The features were extracted from a statewide data set downloaded from the United States Census Bureau by Metropolitan Transportation Commission staff.The purpose of this feature layer is for the production of feature sets for public access and download to avoid licensing issues related to the agency's base data.Source data downloaded from https://www.census.gov/geographies/mapping-files/time-series/geo/tiger-line-file.html_The TIGER/Line Files are shapefiles and related database files (.dbf) that are an extract of selected geographic and cartographic information from the United States Census Bureau's Master Address File/Topologically Integrated Geographic Encoding and Referencing (MAF/TIGER) Database (MTDB). The MTDB represents a seamless national file with no overlaps or gaps between parts, however, each TIGER/Line File is designed to stand alone as an independent data set, or they can be combined to cover the entire nation.Census tracts are small, relatively permanent statistical subdivisions of a county or equivalent entity, and were defined by local participants as part of the Census 2020 Participant Statistical Areas Program (PSAP). The Census Bureau delineated the census tracts in situations where no local participant existed or where all the potential participants declined to participate. The primary purpose of census tracts is to provide a stable set of geographic units for the presentation of census data and comparison back to previous decennial censuses. Census tracts generally have a population size between 1,500 and 8,000 people, with an optimum size of 4,000 people.When first delineated, census tracts were designed to be homogeneous with respect to population characteristics, economic status, and living conditions. The spatial size of census tracts varies widely depending on the density of settlement. Physical changes in street patterns caused by highway construction, new development, etc. may require boundary revisions before a census. In addition, census tracts occasionally are split due to population growth, or combined as a result of substantial population decline. Census tract boundaries generally follow visible and identifiable features. They may follow legal boundaries such as minor civil division (MCD) or incorporated place boundaries in some States and situations to allow for census tract-to-governmental unit relationships where the governmental boundaries tend to remain unchanged between censuses. State and county boundaries are always census tract boundaries in the standard census geographic hierarchy. In a few rare instances, a census tract may consist of noncontiguous areas. These noncontiguous areas may occur where the census tracts are coextensive with all or parts of legal entities that are themselves noncontiguous.

2020 Census tracts for the San Francisco Bay Region. Features were extracted from California 2021 TIGER/Line shapefile by the Metropolitan Transportation Commission.Census tracts are small, relatively permanent statistical subdivisions of a county or equivalent entity, and were defined by local participants as part of the 2020 Census Participant Statistical Areas Program. The Census Bureau delineated the census tracts in situations where no local participant existed or where all the potential participants declined to participate. The primary purpose of census tracts is to provide a stable set of geographic units for the presentation of census data and comparison back to previous decennial censuses.Census tracts generally have a population size between 1,200 and 8,000 people, with an optimum size of 4,000 people. When first delineated, census tracts were designed to be homogeneous with respect to population characteristics, economic status, and living conditions. The spatial size of census tracts varies widely depending on the density of settlement. Physical changes in street patterns caused by highway construction, new development, and so forth, may require boundary revisions. In addition, census tracts occasionally are split due to population growth, or combined as a result of substantial population decline.Census tract boundaries generally follow visible and identifiable features. They may follow legal boundaries such as minor civil division (MCD) or incorporated place boundaries in some States and situations to allow for census tract-to-governmental unit relationships where the governmental boundaries tend to remain unchanged between censuses. State and county boundaries always are census tract boundaries in the standard census geographic hierarchy.In a few rare instances, a census tract may consist of noncontiguous areas. These noncontiguous areas may occur where the census tracts are coextensive with all or parts of legal entities that are themselves noncontiguous.For the 2010 Census and beyond, the census tract code range of 9400 through 9499 was enforced for census tracts that include a majority American Indian population according to Census 2000 data and/or their area was primarily covered by federally recognized American Indian reservations and/or off-reservation trust lands; the code range 9800 through 9899 was enforced for those census tracts that contained little or no population and represented a relatively large special land use area such as a National Park, military installation, or a business/industrial park; and the code range 9900 through 9998 was enforced for those census tracts that contained only water area, no land area.The Census Bureau uses suffixes to help identify census tract changes for comparison purposes. Local participants have an opportunity to review the existing census tracts before each census. If local participants split a census tract, the split parts usually retain the basic number, but receive different suffixes. In a few counties, local participants request major changes to, and renumbering of, the census tracts. Changes to individual census tract boundaries usually do not result in census tract numbering changes.Relationship to Other Geographic Entities—Within the standard census geographic hierarchy, census tracts never cross state or county boundaries, but may cross the boundaries of county subdivisions, places, urban areas, voting districts, congressional districts, and American Indian, Alaska Native, and Native Hawaiian areas.

description: The federal and state endangered California clapper rail, Rallus longirostris obsoletus. is a species that, until very recently, was on the verge of extinction. This secretive marsh bird's decline began over 100 years ago in the pristine marshes of San Francisco Bay (Bay) and the California coast (Fig. 1). In the earlier part of this century, the rail was found as far north as Humboldt Bay pd as far south as Morro Bay (Gill 1979) (Fig. 2). In the early 80s, the last known pair of rails outside of the Bay was seen at Elkhorn Slough in Monterey County. During the first half of this century, exploitation of the Bay's natural resources, including unrestricted filling and diking of the tidal marshes, began shrinking the rail's habitat in San Pablo Bay, Central and South San Francisco Bay from over 51,000 hectares to less than 9,000 hectares that now remain today (Dedrick 1993). The cumulative effects from this continued loss of critical habitat, combined with recent threats from increased predation, probable contamination, and other stresses associated with expanding urban growth, has created a crisis for our bay's indigenous rail. After the rail was listed as Endangered under the authority of the Endangered Species Act by the U.S. Fish and Wildlife Service (Service) in 1970, censuses of the population in the Bay were initiated. In the early 1970s, Gill estimated the total California clapper rail population at 4200 to 6000 individuals (1979). Surveys for the rail continued into the 80s (Moss 1980), with Harvey providing an estimate of 1200-1500 rails in 1981. The survey by Harvey was more accurate than the Gill estimate because an actual count was made, as compared to an average density which Gill applied to all suitable habitat. Subsequent censuses were sporadic and incomplete (Harvey 1987) until the Service, led by the San Francisco Bay National Wildlife Refuge (Refuge) began winter high tide surveys of South San Francisco Bay (South Bay) in 1988 (Foerster 1989). The Service began to suspect that the rail was in serious decline after the Refuge conducted a thorough survey of major South Bay marshes in the winter of 1988-89 and estimated a total population of only 700 rails. It was discovered that populations of rails in marshes on the east side of the bay were suffering the greatest declines and that predation by non-native predators was implicated as a primary factor (Foerster 1989). This hypothesis was confirmed by data collected by the Refuge and subsequently an Environmental Assessment and Predator Management Plan was implemented in March 1991 (Foerster and Takekawa 1991). Since 1988, the Refuge has continued to conduct annual winter high tide surveys of South Bay rail populations and some San Pablo Bay (North Bay) subpopulations (Figs. 2 and 3), with the assistance of the California Department of Fish and Game (CDFG) and other local organizations such as the San Francisco Bay Bird Observatory. This report summarizes data collected between November 1989 and January 1993, encompassing four annual winter surveys. During the last two years, the Refuge also initiated research into several factors which were implicated in rail population decline. The factors which were identified as significantly affecting rail survival included predation by non-native predators (Foerster and Takekawa 1991), and high levels of heavy metals in prey species (Lonzarich, et al. 1992). Continued analysis of these factors by the Service will culminate in a several reports to be released in late 1994.; abstract: The federal and state endangered California clapper rail, Rallus longirostris obsoletus. is a species that, until very recently, was on the verge of extinction. This secretive marsh bird's decline began over 100 years ago in the pristine marshes of San Francisco Bay (Bay) and the California coast (Fig. 1). In the earlier part of this century, the rail was found as far north as Humboldt Bay pd as far south as Morro Bay (Gill 1979) (Fig. 2). In the early 80s, the last known pair of rails outside of the Bay was seen at Elkhorn Slough in Monterey County. During the first half of this century, exploitation of the Bay's natural resources, including unrestricted filling and diking of the tidal marshes, began shrinking the rail's habitat in San Pablo Bay, Central and South San Francisco Bay from over 51,000 hectares to less than 9,000 hectares that now remain today (Dedrick 1993). The cumulative effects from this continued loss of critical habitat, combined with recent threats from increased predation, probable contamination, and other stresses associated with expanding urban growth, has created a crisis for our bay's indigenous rail. After the rail was listed as Endangered under the authority of the Endangered Species Act by the U.S. Fish and Wildlife Service (Service) in 1970, censuses of the population in the Bay were initiated. In the early 1970s, Gill estimated the total California clapper rail population at 4200 to 6000 individuals (1979). Surveys for the rail continued into the 80s (Moss 1980), with Harvey providing an estimate of 1200-1500 rails in 1981. The survey by Harvey was more accurate than the Gill estimate because an actual count was made, as compared to an average density which Gill applied to all suitable habitat. Subsequent censuses were sporadic and incomplete (Harvey 1987) until the Service, led by the San Francisco Bay National Wildlife Refuge (Refuge) began winter high tide surveys of South San Francisco Bay (South Bay) in 1988 (Foerster 1989). The Service began to suspect that the rail was in serious decline after the Refuge conducted a thorough survey of major South Bay marshes in the winter of 1988-89 and estimated a total population of only 700 rails. It was discovered that populations of rails in marshes on the east side of the bay were suffering the greatest declines and that predation by non-native predators was implicated as a primary factor (Foerster 1989). This hypothesis was confirmed by data collected by the Refuge and subsequently an Environmental Assessment and Predator Management Plan was implemented in March 1991 (Foerster and Takekawa 1991). Since 1988, the Refuge has continued to conduct annual winter high tide surveys of South Bay rail populations and some San Pablo Bay (North Bay) subpopulations (Figs. 2 and 3), with the assistance of the California Department of Fish and Game (CDFG) and other local organizations such as the San Francisco Bay Bird Observatory. This report summarizes data collected between November 1989 and January 1993, encompassing four annual winter surveys. During the last two years, the Refuge also initiated research into several factors which were implicated in rail population decline. The factors which were identified as significantly affecting rail survival included predation by non-native predators (Foerster and Takekawa 1991), and high levels of heavy metals in prey species (Lonzarich, et al. 1992). Continued analysis of these factors by the Service will culminate in a several reports to be released in late 1994.

About this dataset

Context

The dataset tabulates the San Francisco township population over the last 20 plus years. It lists the population for each year, along with the year on year change in population, as well as the change in percentage terms for each year. The dataset can be utilized to understand the population change of San Francisco township across the last two decades. For example, using this dataset, we can identify if the population is declining or increasing. If there is a change, when the population peaked, or if it is still growing and has not reached its peak. We can also compare the trend with the overall trend of United States population over the same period of time.

Key observations

In 2023, the population of San Francisco township was 862, a 0.69% decrease year-by-year from 2022. Previously, in 2022, San Francisco township population was 868, a decline of 0.69% compared to a population of 874 in 2021. Over the last 20 plus years, between 2000 and 2023, population of San Francisco township decreased by 36. In this period, the peak population was 923 in the year 2009. The numbers suggest that the population has already reached its peak and is showing a trend of decline. Source: U.S. Census Bureau Population Estimates Program (PEP).

Content

When available, the data consists of estimates from the U.S. Census Bureau Population Estimates Program (PEP).

Data Coverage:

• From 2000 to 2023

Variables / Data Columns

• Year: This column displays the data year (Measured annually and for years 2000 to 2023)
• Population: The population for the specific year for the San Francisco township is shown in this column.
• Year on Year Change: This column displays the change in San Francisco township population for each year compared to the previous year.
• Change in Percent: This column displays the year on year change as a percentage. Please note that the sum of all percentages may not equal one due to rounding of values.

Good to know

Margin of Error

Data in the dataset are based on the estimates and are subject to sampling variability and thus a margin of error. Neilsberg Research recommends using caution when presening these estimates in your research.

Custom data

If you do need custom data for any of your research project, report or presentation, you can contact our research staff at research@neilsberg.com for a feasibility of a custom tabulation on a fee-for-service basis.

Inspiration

Neilsberg Research Team curates, analyze and publishes demographics and economic data from a variety of public and proprietary sources, each of which often includes multiple surveys and programs. The large majority of Neilsberg Research aggregated datasets and insights is made available for free download at https://www.neilsberg.com/research/.

Recommended for further research

This dataset is a part of the main dataset for San Francisco township Population by Year. You can refer the same here

Tracts; January 1, 2019 vintage; Generalized

Features provide a view of 2020 Census tracts for the San Francisco Bay Region. Features are a subset of the Census Tracts 500k service at https://data.bayareametro.gov/dataset/Census-Tracts-500K/dg5p-pxcu.

Census tracts are small, relatively permanent statistical subdivisions of a county or equivalent entity, and were defined by local participants as part of the 2020 Census Participant Statistical Areas Program. The Census Bureau delineated the census tracts in situations where no local participant existed or where all the potential participants declined to participate. The primary purpose of census tracts is to provide a stable set of geographic units for the presentation of census data and comparison back to previous decennial censuses.

Census tracts generally have a population size between 1,200 and 8,000 people, with an optimum size of 4,000 people. When first delineated, census tracts were designed to be homogeneous with respect to population characteristics, economic status, and living conditions. The spatial size of census tracts varies widely depending on the density of settlement. Physical changes in street patterns caused by highway construction, new development, and so forth, may require boundary revisions. In addition, census tracts occasionally are split due to population growth, or combined as a result of substantial population decline.

Census tract boundaries generally follow visible and identifiable features. They may follow legal boundaries such as minor civil division or incorporated place boundaries in some States and situations to allow for census tract-to-governmental unit relationships where the governmental boundaries tend to remain unchanged between censuses. State and county boundaries always are census tract boundaries in the standard census geographic hierarchy.

In a few rare instances, a census tract may consist of noncontiguous areas. These noncontiguous areas may occur where the census tracts are coextensive with all or parts of legal entities that are themselves noncontiguous.

For the 2010 Census and beyond, the census tract code range of 9400 through 9499 was enforced for census tracts that include a majority American Indian population according to Census 2000 data and/or their area was primarily covered by federally recognized American Indian reservations and/or off-reservation trust lands; the code range 9800 through 9899 was enforced for those census tracts that contained little or no population and represented a relatively large special land use area such as a National Park, military installation, or a business/industrial park; and the code range 9900 through 9998 was enforced for those census tracts that contained only water area, no land area.

The Census Bureau uses suffixes to help identify census tract changes for comparison purposes. Local participants have an opportunity to review the existing census tracts before each census. If local participants split a census tract, the split parts usually retain the basic number, but receive different suffixes. In a few counties, local participants request major changes to, and renumbering of, the census tracts. Changes to individual census tract boundaries usually do not result in census tract numbering changes.

Relationship to Other Geographic Entities—Within the standard census geographic hierarchy, census tracts never cross state or county boundaries, but may cross the boundaries of county subdivisions, places, urban areas, voting districts, congressional districts, and American Indian, Alaska Native, and Native Hawaiian areas.

Cartographic Census Tracts for the San Francisco Bay Region. Tracts are of the 2010-2019 vintage (Census 2010). Water areas, such as the ocean and bays are removed.

Census tracts are small, relatively permanent statistical subdivisions of a county or equivalent entity, and were defined by local participants as part of the 2010 Census Participant Statistical Areas Program. The Census Bureau delineated the census tracts in situations where no local participant existed or where all the potential participants declined to participate. The primary purpose of census tracts is to provide a stable set of geographic units for the presentation of census data and comparison back to previous decennial censuses.

Census tracts generally have a population size between 1,200 and 8,000 people, with an optimum size of 4,000 people. When first delineated, census tracts were designed to be homogeneous with respect to population characteristics, economic status, and living conditions. The spatial size of census tracts varies widely depending on the density of settlement. Physical changes in street patterns caused by highway construction, new development, and so forth, may require boundary revisions. In addition, census tracts occasionally are split due to population growth, or combined as a result of substantial population decline.

Census tract boundaries generally follow visible and identifiable features. They may follow legal boundaries such as minor civil division or incorporated place boundaries in some States and situations to allow for census tract-to-governmental unit relationships where the governmental boundaries tend to remain unchanged between censuses. State and county boundaries always are census tract boundaries in the standard census geographic hierarchy.

description: Fragmentation and loss of natural habitat have important consequences for wild populations and can negatively affect long-term viability and resilience to environmental change. Salt marsh obligate species, such as those that occupy the San Francisco Bay Estuary in western North America, occupy already impaired habitats as result of human development and modifications and are highly susceptible to increased habitat loss and fragmentation due to global climate change. We examined the genetic variation of the California Ridgway s rail ( Rallus obsoletus obsoletus), a state and federally endangered species that occurs within the fragmented salt marsh of the San Francisco Bay Estuary. We genotyped 107 rails across 11 microsatellite loci and a single mitochondrial gene to estimate genetic diversity and population structure among seven salt marsh fragments and assessed demographic connectivity by inferring patterns of gene flow and migration rates. We found pronounced genetic structuring among four geographically separate genetic clusters across the San Francisco Bay. Gene flow analyses supported a stepping stone model of gene flow from south-to-north. However, contemporary gene flow among the regional embayments was low. Genetic diversity among occupied salt marshes and genetic clusters were not significantly different. However, we detected low effective population sizes and significantly high relatedness among individuals within salt marshes. Preserving genetic diversity and connectivity throughout the San Francisco Bay may require attention to salt marsh restoration in the Central Bay where habitat is both most limited and most fragmented. Incorporating periodic genetic sampling in to the management regime may help evaluate population trends and guide long-term management priorities. These data support the following in-press publication: Wood, D.A., Bui, T.D., Overton, C.T., Vandergast, A.G., Casazza, M.L., Hull, J.M., and Takekawa, J.Y. Conservation Genetics (2016). doi:10.1007/s10592-016-0888-4.; abstract: Fragmentation and loss of natural habitat have important consequences for wild populations and can negatively affect long-term viability and resilience to environmental change. Salt marsh obligate species, such as those that occupy the San Francisco Bay Estuary in western North America, occupy already impaired habitats as result of human development and modifications and are highly susceptible to increased habitat loss and fragmentation due to global climate change. We examined the genetic variation of the California Ridgway s rail ( Rallus obsoletus obsoletus), a state and federally endangered species that occurs within the fragmented salt marsh of the San Francisco Bay Estuary. We genotyped 107 rails across 11 microsatellite loci and a single mitochondrial gene to estimate genetic diversity and population structure among seven salt marsh fragments and assessed demographic connectivity by inferring patterns of gene flow and migration rates. We found pronounced genetic structuring among four geographically separate genetic clusters across the San Francisco Bay. Gene flow analyses supported a stepping stone model of gene flow from south-to-north. However, contemporary gene flow among the regional embayments was low. Genetic diversity among occupied salt marshes and genetic clusters were not significantly different. However, we detected low effective population sizes and significantly high relatedness among individuals within salt marshes. Preserving genetic diversity and connectivity throughout the San Francisco Bay may require attention to salt marsh restoration in the Central Bay where habitat is both most limited and most fragmented. Incorporating periodic genetic sampling in to the management regime may help evaluate population trends and guide long-term management priorities. These data support the following in-press publication: Wood, D.A., Bui, T.D., Overton, C.T., Vandergast, A.G., Casazza, M.L., Hull, J.M., and Takekawa, J.Y. Conservation Genetics (2016). doi:10.1007/s10592-016-0888-4.

Since the turn of the century, the United States has undergone a redistribution of population from rural and rust belt counties to urban counties; particularly those along the Northern and Southern Atlantic Seaboard, the Pacific Coast and parts of the Southwest region. 41 percent or 1,295 counties had population declines from 2000 to 2016, with 15 counties experiencing declines of more than 25,000 people or 2.4 percent of the total population.Over the same period, total population for the nation grew by 42 million, 8 percent of which has migrated from declining rural and rust belt counties to growing urban counties along the East and West Coast, and in the Southwest, resulting in a 23 percent increase in population occurring in 60 percent of counties in the United States. The data indicates that the majority of this growth is occurring in just 12 percent of counties, including the San Francisco Bay Region which has experienced a 2.4 percent increase in population.

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 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 seven 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 one of three 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 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.