Invasive Species
Stellwagen Bank

photo of didemnum
Tunicate colonies of Didemnum encrusted on boulders. Credit: USGS

Why is it a concern?

Invasive species exist in the sanctuary and have for many decades. However, their abundance and distribution have not been documented. Most recently, the invasive tunicate Didemnum sp. was observed in the sanctuary. Monitoring the trends of this and other invasive species is important as a step in preventing unnatural changes in ecosystem structure and function.

Introduced species in the marine and estuarine environment can alter species composition, threaten the abundance and diversity of native marine species, interfere with the ecosystem's function, and disrupt commercial and recreational activities. They can cause local extinction of native species either by preying on them directly or by out-competing them for food or space. Once established, non-indigenous species can be difficult to eradicate. They also exacerbate biotic homogenization, the process of communities becoming more similar due to growing proportion of shared non-native species.

In addition to known vectors for species introduction (e.g., vessels, mobile equipment, drifting debris, and intentional transport of animals and plants), there is concern that climate change will promote the spread of introduced species into areas where they may have previously been restricted. In addition to documenting and eradicating introduced species when possible, a coordinated effort is needed to compile existing information and data, identify data gaps, and update maps of abundance and distribution. It is also necessary to identify the pathways by which new species are introduced into the sanctuary, and prioritize which pathways pose the greatest threat to sanctuary resources.

Science Needs and Questions

There is a need for monitoring the trends of Didemnum and other invasive species, as well as their effects on sanctuary resources. In addition, these questions apply to the sanctuary.

  • What non-indigenous and invasive species can be found living in and around the SBNMS?
  • What is the status of non-indigenous species? Is it changing?
  • From where are non-indigenous species coming from?
  • How can key non-indigenous species be controlled and prevented from becoming invasive?
  • What impacts are non-native species having on the resources of the Sanctuary?
  • What appropriate management actions need to be taken as a result of non-indigenous and invasive species?


Byrnes, J. E., P.L. Reynolds and J.L. Stachowicz. 2007. Invasions and extinctions reshape coastal marine food webs. PLoS ONE 2(3): e295. doi:10.1371/journal.pone.0000295.

Lockwood, J.L., M.F. Hoopes, M.P. Marchetti. 2007. Invasion Ecology. Blackwell Publishing, Malden, MA.

National Marine Sanctuary Program. 2007. Gerry E. Studds Stellwagen Bank National Marine Sanctuary Condition Report 2007. U.S. Department of Commerce, National Oceanic and Atmospheric Administration, National Marine Sanctuary Program, Silver Spring, MD. 41 pp.

Sax, D.F., J.J. Stachowicz, S.D. Gaines. 2005. Species invasions: Insight into ecology, evolution, and biogeography. Sinauer Associates, Inc. Sunderland, MA.