The Chesapeake Bay Introduced Species Database Project Has Ended

The Chesapeake Bay Database project ended in 2020. This site will remain available for historical reference, but the database has not been updated since 2020 and will not receive any further updates. For up to date information on introduced marine and estuarine invertebrates and algae in Chesapeake Bay, please visit the NEMESIS North American database.

Experienced users of the Chesapeake Bay database should carefully read the next section to learn what to expect when consulting the NEMESIS North American database.

Migrating to the NEMESIS North American database

Users migrating from the Chesapeake Bay database should be aware that there are a few key differences in the scope of information included in the NEMESIS North American database.

Taxonomic Scope and Habitat Coverage

The North American database focuses on introduced marine and estuarine invertebrates and algae. The Chesapeake Bay database included species from nearly all taxonomic groups and included some terrestrial species and vascular plants.

For a small number of critically important species that fall outside of the North American database’s usual taxonomic scope, we plan to migrate information from the Chesapeake Bay database into the North American database. However, users should be aware that the following groups are not generally included in the North American database:

  • terrestrial species
  • estuarine and marine birds, fishes, mammals, or reptiles
  • vascular plants

To learn more about our data migration plans, please contact:

Population Status

The Chesapeake Bay database included species that are established, failed, extinct, and cryptogenic (meaning the native/introduced status is unclear) within Chesapeake Bay. The North American database includes introduced species with established populations within the United States’ North American territorial boundaries. Cryptogenic species, failed introductions, and extinct introduced species are not included.

Chesapeake-specific Details

The Chesapeake Bay database included structured information on residency (the time a species spends in the Bay system). Within the North American database’s species profiles, details on Chesapeake Bay residency is not an explicit focus and may be included only in narrative comments or not at all.

About the Chesapeake Bay Database

The Chesapeake Bay Introduced Species Database project began in YEAR and was intended to provide a comprehensive source of information on species introduced to Chesapeake Bay and adjacent Atlantic waters and coastal bays. It was developed by the Marine Invasions Research Lab of the Smithsonian Environmental Research Center. The Chesapeake Bay database also acted as a first installment and proof-of-concept for the National Estuarine Marine and Exotic Species Information System (NEMESIS), launched in YEAR. NEMESIS has since grown to encompass a database covering all of North America (including Chesapeake Bay), plus databases developed in collaboration with research partners to focus on other geographic regions of interest.

The Chesapeake Bay database project ended in 2020. NEMESIS now contains the newest and most up to date information on marine and estuarine invertebrates and algae introduced to Chesapeake Bay. This site remains available for historical reference, but it has not received updates since the project ended and will not receive further updates.

The Chesapeake Bay database includes species from nearly all taxonomic groups (protozoans, algae, plants, invertebrates, fish, birds and mammals) from diverse habitats. The coverage area includes Chesapeake Bay and its tributaries up to the head of tidewater, tidal wetlands up to the monthly mean high-tide line, and adjacent Atlantic waters and coastal bays. Species are included if they have been verified as occurring within the tidal waters and wetlands of the Chesapeake Bay region, as well as some potential invaders such as the Zebra Mussel (Dreissena polymorpha). Terrestrial species are generally excluded, but there are some exceptions. For example, some terrestrial species such as Garden Asparagus (Asparagus officinalis) and House Mouse (Mus musculus) are included because they occur in tidal marshes.

As of September 2008 the database included 321 species that have been reported in the tidal waters and wetlands of the Chesapeake Bay. Of these 321 species, 176 are introduced with established populations in region. These include species regularly occurring in tidal waters (regular residents, 125 species), and species that occur largely outside the estuary (boundary residents, 51 species). In addition, the database lists species unsuccessfully introduced to the region (failed, 25 species, or extinct, 5 species), species of uncertain establishment (unknown, 37 species), some potential invaders, known from the watershed, but unconfirmed in tidal waters (21 species), and prominent cryptogenic species (possibly native, possibly introduced, 54 species). Information on invasion status and establishment of each species is given on its invasion history.

Citing the Chesapeake Bay Database

We ask that people who are planning extensive analyzes of this database please contact for permission and to discuss interpretations of the data.

This database should be cited as:

Fofonoff PW, Ruiz GM, Steves B, Hines AH, Carlton JT. 2020. National Exotic Marine and Estuarine Species Information System: Chesapeake Bay Introduced Species Database. [accessed ].

Browsing & Searching

Use the "Summaries" navigation menu to browse the database. Of particular note, the All Taxa page contains a list of all species in the database, while the Groups page allows the user to browse by major taxonomic group.

The database can also be searched using the search box in the menu bar, which matches the text entered against both the scientific and common names defined for each species in the database. You can search using fragmentary search terms: entering nem will bring up Nematostella vectensis and Bonnemaisonia hamifera, but also Diadumene lineata (common name: Striped Sea Anemone) and Anguillicoloides crassus (common name: Nematode).

IMPORTANT! There is no way to limit the search to only species that are introduced with established populations in the Chesapeake Bay region. In order to compile such a list, you will need to review each species’ profile, where its status is listed under the invasion history section. Additionally, there is no way to automatically generate a list of species introduced to a certain region of the watershed or coastal bays, although there is information regarding a species’ range under the invasion history and ecology sections of its profile.

Invasion History/Status Fields

The Invasion History section for each species contains information about its status. We know the introduced or native status of species with varying degrees of certainty. In some cases, deliberate introductions or accidental escapes are well-documented. In other cases, a variety of criteria including human transport, relation to the previously known range, fossil distribution, rapid range expansions, etc., can be used to determine the status of a species. For most species, except for a few potential invaders, there is a date of first record. This could be the date of first collection, sighting, or documented deliberate release or the date of writing or publication. However, for many organisms the question of native versus introduced origin cannot be resolved, in these cases the word “cryptogenic” is used.

Invasion Status


Species are considered introduced if the introduction is historically documented, or else is strongly supported by a wide range of biogeographic, ecological, and/or genetic criteria.

We have included freshwater fishes and a turtle that are native or cryptogenic in a small part of the Chesapeake Bay watershed (usually the James River and Dismal Swamp drainages), but have been introduced in much larger portions of the basin and its tidal tributaries. We have also included two species of waterfowl the Canada Goose (Branta canadensis) and Mallard Duck (Anas platyrhynchos), whose wintering populations are native, but whose resident breeding populations consist largely of introduced birds of different genetic stock.

Native & Introduced
Some species that are native to large portions of the Chesapeake Bay watershed or the adjacent Atlantic but have been introduced to small areas of tidal waters and wetlands outside their normal Chesapeake Bay range. Examples include Bald Cypress (Taxodium distichum) and Bowfin (Amia calva), which have extensive ranges on the southern Coastal Plain of the Chesapeake watershed but have been introduced in scattered locations in northern parts of the Bay and its watershed.

Introduced status is suspected, but evidence is insufficient to confirm it. For some taxa experts have conflicting opinions about their introduced/native status in North America or the Chesapeake Bay region.

The cryptogenic species in our database are selected because they are high-profile with multiple features suggesting, but not confirming, introduced status. Examples: Water-Pepper (Polygonum hydropiper); Dermo (Perkinsus marinu, disease of oysters); Sea Grapes (Molgula manhattensis, a tunicate); Bluntnose Minnow (Pimephales notatus).

Population Status

These species have been repeatedly collected and there is evidence of successful reproduction in the Chesapeake Bay region and/or the immediately adjacent watershed. Our minimum criterion to determine establishment of some poorly studied organisms, such as some marine invertebrates and algae, was that a species be found either in two separate locations or in two collections in separate years in the same location. For better-known organisms, such as shelled mollusks, fishes and flowering plants, we used stricter criteria.

These species have been found in only one location or collection within the past 50 years, and/or have uncertain reproductive capacity.

For most species in this category, collecting and/or taxonomic information has been insufficient to determine whether reproducing populations exist; examples include Lesser Pond-Sedge (Carex acutissima), solitary tunicate (Ascidiella aspersa), and littoral woodlouse (Halophiloscia couchii). In other cases, the organism’s reproductive ability is uncertain, such as with artificially produced hybrids (Palmetto Bass, Hybrid Striped Bass, Morone saxatilis X M. chrysops) and triploid individuals (Suminoe Oyster, Crassostrea ariakensis), or reproduction is unlikely because of environmental mismatches (Northern Pike, Esox lucius).

Reproducing populations appear to have existed in the Chesapeake Bay region but have apparently died out. Examples include: Cyperus fuscus (Brown Flatsedge); Tinca tinca (Tench, a fish); Rattus rattus (Black Rat).
These species were introduced to the region, but there is no evidence of prolonged survival or reproduction. In many cases, failure was inferred from a mismatch between the species' environmental tolerances and Chesapeake Bay conditions. Examples include: Oncorhynchus tshawytscha (Chinook Salmon) Caiman crocodilus (Common Caiman).


This field separates species according to the degree to which they maintain populations in Chesapeake Bay region. We separated species into three categories based on their frequency of occurrence or residency:

Regular Residents
Maintain substantial populations year-round or require tidal waters and wetlands to complete their life cycle. Examples: Hydrilla (Hydrilla verticillata); Asian Shore crab (Hemigrapsus sanguineus); Common Carp (Cyprinus carpio); Nutria (Myocastor coypus).
Boundary Residents
Maintain the bulk of their populations in nontidal freshwater habitats or in terrestrial environments but occur in tidal waters and wetlands. Examples: Asparagus (Asparagus officinalis); Stable fly (Stomoxys calcitrans); Brown trout (Salmo trutta); Sika deer (Cervus nippon).
Unconfirmed residents
Are established in the watershed, and are suspected of either occurring in tidal waters and wetlands, or of invading tidal regions in the future. However, we have not found sufficient data to confirm the existence of populations of these organisms in tidal waters. We expect that future studies will confirm the presence of some of these species in tidal waters and wetlands. Examples: Water-starwort (Callitriche stagnalis); Zebra mussel (Dreissena polymorpha).

Native and Source Region

For species of estuarine-marine origin, we used ocean regions as categories for native regions and source regions. For species that are predominantly terrestrial and freshwater, we used continental categories. In most cases, these categories are distinct and straightforward. However, some organisms cross salinity and habitat boundaries, and so require somewhat arbitrary choices.

Native Region
The native region of a species is its assumed original range before its transport by humans. In many cases, a species has been so widely spread by human activities that its original range is unknown. In a few cases, we are unsure of the taxonomic identity of a species (e.g., Favorinus sp., Gitanopsis sp.), though we consider the species an introduction in the Chesapeake Bay region because of its absence in previous surveys. In these cases, resolving the species’ identity may clarify its native region.
Source Region

The source region represents the likely source of the introduced population. If the first documented record of a species outside its native range is in Chesapeake Bay, then we choose the native region as the source region.

When a species’ native range covers many geographical regions, historical, morphological, or genetic evidence permits us to select one particular region as the source. For example, many vascular plants introduced to Chesapeake Bay have broad distributions including Europe, Asia, North Africa, and Australia. However, shipping and trade patterns suggest Europe as the source region of most of these species. Many invasions result from several successive events, which future genetic and molecular studies may help to resolve.

Vector(s) of Introduction

Most of the species in our database had possible alternative modes of introduction and a few cases had multiple introductions by different mechanisms (e.g., a fish introduced both by stocking and hatchery escapes). In these cases of multiple introductions, we chose the mechanism responsible for the first introduction.