About the Chesapeake Bay Database

This Chesapeake Bay Introduced Species Database is the first installment of the National Estuarine and Marine Exotic Species Information System (NEMESIS), developed by the Marine Invasions Research Laboratory, at the Smithsonian Environmental Research Center. This database is intended to provide a comprehensive source of information on species introduced to Chesapeake Bay and adjacent Atlantic waters and coastal bays. We are updating the database continually as new introductions are discovered in the region and as new information about existing invaders becomes available. Additional components of NEMESIS will be added, including a database summarizing a survey of fouling organisms in U.S. harbors, a database on marine/estuarine invasions literature, and a national database on marine/estuarine invasions.

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.

We ask that people who are planning extensive analyzes of this database, contact Paul Fofonoff (fofonoffp@si.edu) for permission and interpretations of the data.

This database should be cited as:

Fofonoff, P.W., Ruiz, G. M., Steves, B., Hines, A.H.; Carlton, J. T. . National Exotic Marine and Estuarine Species Information System: Chesapeake Bay Introduced Species Database: http://invasions.si.edu/nemesis/chesapeake.html Access Date:

Searching the Database

The database can be searched by (1) Taxonomic Group, with a pull-down menu, e.g. "Algae", "Plants", "Fishes", etc., or "all" for a list of all species; (2) Common Name (e.g., "Green Crab"), (3) Scientific Name (e.g., Carcinus maenas). For common and scientific names, typing a few letters is sufficient to narrow down the selection. Two or more categories can be searched at once to narrow the selection (e.g. "Plants" under Taxonomic Group and "grass" under Common Name, to get a list of plants with "grass" in their names. Clicking "Submit" will give you a species list of species that shows introduced species in red and cryptogenic species in green.

IMPORTANT! In this version of the databases, users cannot sort by invasion status. For example there is no way to limit the search to only species that are introduced with established populations in region. In order to generate such a list you will need to review the species status, which is listed under 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.

Invasion History/Status

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

Introduced - 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), Bowfin (Amia calva) that 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.

Cryptogenic - 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

Established - 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.

Unknown - 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), triploid individuals (Suminoe Oyster, Crassostrea ariakensis), or reproduction is unlikely because of environmental mismatches (Northern Pike, Esox lucius).

Extinct - 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).

Failed - 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 verticillata (Hydrilla); Hemigrapsus sanguineus (Asian Shore Crab), Cyprinus carpio (Common Carp); Myocastor coypus (Nutria).

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 officinalis (Asparagus); Stomoxys calcitrans (Stable Fly); Salmo trutta (Brown Trout); Cervus nippon (Sika Deer).

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 include: Callitriche stagnalis (Water-Starwort); Dreissena polymorpha (zebra mussel).

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; Europe, Asia, North Africa, Australia. However, shipping and trade patterns suggest Europe as the source region of most of these species. Many invasions involve result from several successive events, which future genetic and molecular studies may help to resolve.

Vector(s) of Introduction

Vectors of introduction are listed in the table below (Table 1), together with summaries of the kinds of evidence that were used to support their assignment. 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.