Biological Invasions

, Volume 20, Issue 1, pp 87–103 | Cite as

Invasive tunicate restructures invertebrate community on fishing grounds and a large protected area on Georges Bank

  • Katherine A. KaplanEmail author
  • Deborah R. Hart
  • Karen Hopkins
  • Scott Gallager
  • Amber York
  • Richard Taylor
  • Patrick J. Sullivan
Original Paper


Marine invasive species can profoundly alter ecosystem processes by displacing native species and changing community structures. The invasive tunicate Didemnum vexillum was first found on the northern edge of Georges Bank in 1998. It can form encrusting colonies on gravel substrates that are also a preferred habitat for a number of other invertebrates. In this study we used data collected via HabCam, a vessel-towed underwater imaging system, to investigate the distribution of D. vexillum and its relationship to other epibenthic macroinvertebrates in a portion of Georges Bank that includes fishing grounds and an area protected from bottom-fishing. This novel technology provides imaging of epibenthic species distributions in areas of the benthic environment that were previously unobservable. We found that D. vexillum density is negatively correlated with the Atlantic sea scallop (Placopecten magellanicus), barnacles (genus Balanus), the tube anemone (genus Cerianthus), the green sea urchin (Strongylocentrotus droebachiensis), the globular sponge of the genus Polymastia, and Bryozoa. However D. vexillum is positively correlated with Cancer spp. Crabs, the tube forming polychaete, Filograna implexa, and Asterias spp. sea stars. The hypothesis that D. vexillum restructures the invertebrate community is supported by principal components analysis, revealing it as a primary driver of variation in the community when present. Additionally, there is an effect of the closed area as compared to fishing grounds on the structure of the invertebrate community and the abundance of certain species as consistent with previous studies, bottom-fishing affects invertebrate community structure. Principal components analysis revealed that bottom-fishing also appears to weaken clustering among species in the invertebrate community as compared to the community structure in the closed area. Biodiversity in high gravel sites of the epibenthic environment, as measured by the Shannon diversity index, also declined with increasing D. vexillum percent cover, while the open and closed areas were not significantly different in their level of biodiversity. D. vexillum appears to be the key driver of biodiversity decline in the epibenthos when present, rather than other processes such as direct disturbance and extraction from dredging. This research evaluates ecological responses to the presence of an invasive tunicate and suggests that this invasive species is a major force in shaping the ecological interactions in invaded areas.


Essential fish habitat Vessel-towed underwater camera system Sea squirt Non-indigenous species Ascidians Marine protected areas Hurdle models Hierarchical models 



The analysis for this project was conducted as part of dissertation work funded through the National Marine Fisheries Service and Sea Grant (E/MP-23) Population Dynamics Graduate Fellowship: Evaluating Atlantic sea scallop habitat effects from bottom-fishing using the Habitat Mapping Camera System. The data for this project were collected as part of an industry-based survey through the Research Set-Aside program designed to collect information on scallop biomass and habitat (NOAA Award Number: NA12NMF4540040, Scallop Research Set Aside Award Number: 12-SCA-016). A special thanks to B Knuth, D Harvell and L Rudstam and the Sullivan lab group for discussions and their advice on manuscript preparation. We would also like to thank the editor and two anonymous reviewers for Biological Invasions for their detailed reviews and commentary that helped improve this manuscript.


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Copyright information

© Springer International Publishing AG 2017

Authors and Affiliations

  1. 1.Department of Natural ResourcesCornell UniversityIthacaUSA
  2. 2.Coastal and Marine Sciences InstituteUniversity of California at DavisDavisUSA
  3. 3.Northeast Fisheries Science CenterWoods HoleUSA
  4. 4.Arnie’s Fisheries, Inc.New BedfordUSA
  5. 5.Biology DepartmentWoods Hole Oceanographic InstitutionWoods HoleUSA

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