MIT Sea Grant Center for Coastal Resources

Marine Bioinvasions Fact Sheet: Rapid Assessment Survey

What is a Rapid Assessment Survey (RAS)?

An RAS is conducted by a team of marine species experts to identify both native and introduced species found at selected sites. The goal of an RAS is to make a quick assessment of introduced species present and use this information to document their distribution and collect environmental data. In 2000, the RAS was conducted in Rhode Island and Massachusetts. In 2003, the RAS was expanded to include most of the Northeast U.S. from Maine to New York City.
Botrylloides, an introduced species.

How is an RAS conducted?

A team of scientists, each with a different specialty in marine taxonomy, spend approximately one hour on the docks and identify species. A dock master records the scientistsŪ findings and abundance of species at each site. Samples of specimens are usually taken back to the lab, where scientists spend several more hours, to confirm speciesŪ identities. Water quality data such as salinity, dissolved oxygen content, and water temperature is also taken at every site. For online mapping purposes the longitude and latitude of the location is also taken.

What are the implications of an RAS?

The 2000 and 2003 surveys provide a baseline of species in fouling communities and, for those monitored over time, show the changes in introduced and cryptogenic populations versus the native populations. This allows scientists to analyze the spread of the species and predict future changes in the marine population. The introduced species may impact local communities. According to the Aquatic Nuisance Species Task Force website over 15% of introduced species cause serious harm; introduced species negatively impact at least 42% of endangered species; and the cost associated with major introduced species in the USA alone is on the order of $100 billion per year (Lee 2002; Aquatic Nuisance Species Task Force).

What is the difference between native, cryptogenic, and introduced species?

For some species, it can be difficult to identify their origin and determine whether they are native or introduced. Species whose origins cannot be verified are called žcryptogenic.Ó Thus, species known to have been in New England and not identified in other locations before are known as žnativeÓ species while species known to be native in other parts of the world are žintroducedÓ species. There are as many cryptogenic species in New England as introduced species. Shipping routes between Europe and the East Coast provided early settlers with food and goods. Vessels carried solid ballast (rocks, gravel and shale) that were home to many organisms. Unfortunately, data from this time are rare or nonexistent, and we can only guess the origins of some species. The results obtained during the Rapid Assessment Surveys should be disseminated to generate public awareness.
Molgula manhattensis
Molgula manhattensis, an introduced species.

What else can be done about this problem?

The RAS was put together with the intention of assessing the spread of introduced and cryptogenic species to prompt action and bring awareness to the problem. To date, The RAS only covers the Northeast U.S. To be able to address the problem of cryptogenic and introduced species a national, even a global, Rapid Assessment Survey is needed.

What are the limitations of RAS?

Some problems encountered during data collection for an RAS include time of day, season, tidal stage, isolated populations, and unidentifiable species. Species populations vary by season in the Northeast U.S. and may have low numbers in the winter but high numbers in the summer. Because it is only possible to sample a few key sites around the Northeast, there is always the possibility of assessing a population that is an exception to that area, whether there is a higher or lower native to cryptogenic and invasive species ratio. Finally, the hardest problem to overcome in an RAS is the identification of specimens. The nematoda (round worms) and platyhelminthes (flat worms) are especially problematic. Sometimes species are too young, damaged, or not in a reproductive phase to be positively identified.
Didemnum, an introduced species.


The Rapid Assessment Survey is a great start to assessing a much larger problem in the world. With increased shipping trade between countries, this problem could become more dramatic in the future. The need for a global RAS is apparent.


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  this page last updated on: 4 December, 2002