About the National Estuarine and Marine Exotic Species Information System (NEMESIS)

National Estuarine and Marine Exotic Species Information System (NEMESIS), developed by the Marine Invasions Research Laboratory at the Smithsonian Environmental Research Center, provides comprehensive information on approximately 500 introduced marine and estuarine species of invertebrates and algae with established populations in the continental United States. Introductions occur when species are moved beyond their historical geographic range by human activities. Marine and estuarine species have been moved around the world for nearly as long as people have moved around the world. For example, there is evidence that the marine snail Littorina littorea was brought to the northern tip of Newfoundland, Canada with Viking explorers long before European settlement. As trade and colonization increased so did the number of species introductions. Many of the early introductions were a result of hull fouling, dry ballast (rocks and dirt used to weight sailing vessels), intentional introductions to create new fisheries, and unintentional introductions associated with the seafood trade. Overtime, the amount of intentional introductions decreased and dry ballast changed to water ballast as we moved from wooden ships to metal ships. Today shipping and unintentional introductions associated with trade are the primary means of introduction for marine species. Introduced species have fundamentally changed the structure and function of some ecosystems around the world and impact many dimensions of human society. Due to increased trade and globalization the rates and impacts of new invasions appear to have increased dramatically in recent time.

NEMESIS is a complex, yet easy to use, database that provides information at multiple scales of detail. Designed for a diverse audience, from researchers and resource managers to students and the public, NEMESIS is a portal for access to general or specific information on introduced marine species in the United States, including:

In addition to detailed information in NEMESIS, summary reports and graphics are currently available (and under rapid development) to examine more synthetic information, organized by geographic location or taxonomic groups of species. For example, a user can examine (a) the current number and identity of introduced species with established populations for a specific bay or biogeographic region, (b) the mechanism of introduction (or vector) and time of first record associated with a species in a particular taxonomic group or geographic location.

The creation of NEMESIS required years of research and literature review and remains an ongoing project. Records are updated as new species and new research are discovered. Because of the volume of records yet to be reviewed and finalized, we are rolling out the database one taxonomic group at a time, beginning here with tunicates and select crustaceans (crabs, crayfish, shrimp, and barnacles). The following summary provides guidance in how to search the database and a brief description of the type of information provided for each species.


Searching the Database

General Search: individual species records can be found by typing in either the common or scientific names of the species into the form on the main search page. You can also search for all species in a taxonomic group (algae, plants, fishes, tunicates, etc) using the search field. For common and scientific names typing a few letters is sufficient to narrow down the selection.

For more advance searches there are three options:

1. Taxonomic Tree allows those who know taxonomy to browse by classification starting from kingdom and following through to species.

2. Group Report allows users to view summary information on a particular group (tunicates, crabs, shrimp, crayfish , or barnacles for example). The report contains data on the number of species transported through a certain vector (ballast water), across time and by region. Each report also includes a species list with images. You can also access group reports from the general search page results and the individual species records.

3. Bioregion search allows users to view species list for a particular bioregion.

Species Records


This section provides a brief summary of the species including its native and introduced ranges and any related impacts in its introduced range.


This section includes a species description and the complete taxonomic classification, synonymy, and potentially misidentified species. Users will not necessarily be able to identify species based on the descriptions in this section, but papers that provide greater detail are referenced.

Synonyms- A list of previously applied names for the species.  In some cases, where a species has many synonyms (sometimes more than 100), we select the more recent ones and those most likely to be used in US waters.

Potentially Misidentified Species- We have included species ‘lumped’ or confused by experts, and some of those likely to be confused by casual observers.  In many cases, we give the distribution of the species.  The species listed are mostly those native or likely to be introduced to North American continental waters.


In this section, a species distribution map indicates the native and introduced ranges of each species. In some cases, areas where a species was introduced, but is not known to be established (e.g. failed, extinct, or unknown) and locations where a species occurs, but its native/introduced status is uncertain (i.e. cryptogenic) are also shown. Beneath the map is a listing of the first record of introduction into North America, including the West, East and Gulf Coasts combined. This is followed by a general invasion history section containing a detailed account of the history of spread for each species including references to the primary literature.

Bay level distribution detail for the continental United States is available by clicking distribution details beneath the map. By zooming into an introduced bioregion in the distribution map, the watershed or bay level introduction data is revealed. Selecting a watershed or bay will bring up detailed information including the date of first record for the watershed, a listing of specific locations within the bay or watershed where the species has been found, the means of introduction or vector, bay level impacts, and references. Bay level impacts information is not available for all species, but general information on impacts is available at the global scale under the impacts tab of the main species report.


This section of the species record includes general information about the life history of the group to which the species belongs, along with some species specific information if available. In addition, there is a summary table that lists species specific information about habitat, environmental tolerances, reproduction and diet. Users needing more detailed information regarding the ecology of a taxonomic group or a particular species should consult zoology textbooks and the primary literature.


The economic and ecological impacts are reported for each species. Impacts are reported if the introduced species caused a detectable change in the composition or population size of a resident species, or had an economic impact on fisheries resources, agricultural products, infrastructure (docks, dams, water supply, etc.), power plants, shipping or recreation. For many species impacts that meet these criteria have not been reported due to lack of research. General impacts and bay level impacts (e.g., effects on foodwebs or nutrient cycling) are inlcuded, when such data are reported. We caution that the lack of reported impacts should not be interpreted as "no impact occurring"; for most introduced species, there are in fact no studies to evaluate whether or not they have significant effects.


Each record contains an extensive reference list. Users are encouraged to consult the primary literature for more information.


Please use the following citation when referencing NEMESIS.

Fofonoff PW, Ruiz GM, Steves B, Simkanin C, & Carlton JT (2018)
National Exotic Marine and Estuarine Species Information System.
Access Date:


We thank the many scientists, students, resource managers, and staff who have generously contributed time and expertise to help us develop and improve the content of NEMESIS over many years. We also wish to acknowledge the exceptional effort, advice, and patience provided by Rolando Bastida-Zavala, Melissa Frey, Pam Fuller, Francis Kerchoff, Gretchen Lambert, Monaca Noble, Rosana Rocha, Lea-Anne Roberts, and Christina Simkanin.