Mission: Native vs. Invasive Crabs

Research question:

How do the ratios of invasive and native crabs compare up and down the coast of Maine and New Hampshire? Is the ratio of native crabs to invasive crabs changing over time?

Where to look:

All along the coast of ME and NH

Who wants your data:

Elizabeth Stephenson, MMISCo Maine Marine Invasive Species Collaborative

Alyson Eberhardt, NH Sea Grant/University of New Hampshire Cooperative Extension

Species Involved:

Green Crab (

Asian Shore Crab (

Chinese Mitten Crab (

Rock Crab (

Jonah Crab (

You're invited

Scientists across the Northeast are working with local communities to help figure out how widespread the presence of invasive crabs, such as green crabs and Asian shore crabs, are and what impacts they are having on local ecosystems. There is still so much left unstudied in the marine environment and what we know of impacts of these marine invaders remains incomplete. We need more hands on deck to monitor our coastlines and truly investigate the effects these marine invaders may be having on our environment.

Mission Steps

  1. Brush up on your fieldwork skills by doing some of these Fieldwork Skill Stations -
  2. Once you have decided when and where your fieldwork will take place, create a new investigation and student teams. First time doing this? Here is a useful “How-To Guide” - Don’t forget to check when low tide is.
  3. Print the Coastal Species Survey datasheet (
  4. Because each team will be documenting 5 species, you will need to print 3 extra copies of the last page of the datasheet.
  5. Consider having each team member become the “expert” on one species. This will allow for each student to have a focus and only one species to look for rather than 5 at once.
  6. Print these species ID cards:
  7. Green Crab -
  8. Asian Shore Crab -
  9. Chinese Mitten Crab -
  10. Rock Crab -
  11. Jonah Crab -
  12. Gather background information on invasive crabs in your area. Depending on where you are this may simply be background information on how these organisms behave instead of where they have been found.
  13. Check out the Vital Signs map to see where these species have or have not been found (
  14. Click on the “Change Search” button and choose your species
  15. Choose ‘Show ALL Data’
  16. Click ‘Map it’
  17. On the far right of the page, select for only ‘found’ observations.
  18. Look for local news articles that may be related to marine issues, check your state’s fish and game or department of marine protection website
  19. After gathering some background information, make a prediction and have students add this to the field notes of their datasheets.
  20. Do you think you will find any invasive or native crabs? Do you think there will be more of one than another? Explain your prediction.
  21. Gather your fieldwork equipment:
  22. Cameras, iPads, or iPhones (whatever your preferred picture taking devices are)
  23. Enough 1-meter squared quadrats for each student team
  24. Rulers
  25. Pencils
  26. One 20 meter transect line (to create your sampling site)
  27. 2-3 buckets to sort crabs with
  28. Go into the field and collect data (make sure you go at low tide)
  29. Establish your sampling site by following this methodology -
  30. Go through your quadrat, looking under rocks and seaweed, to search for any crabs that may be hiding within your quadrat.
  31. When you find a crab, place it in one bucket (with water in it) to sort later
  32. After you have found all the crabs that are in your quadrat, note the total number of crabs in the field notes section of your Vital Signs datasheet
  33. Now sort your crabs into buckets, using one bucket for each different species you find
  34. Use your Vital Signs ID cards to help you identify which crab species you have
  35. Once you have all your crabs sorted and identified, note the total number of each species of crab you found in the field notes section of your Vital Signs datasheet.
  36. Use your Vital Signs datasheet to collect photo and written evidence to make your claim of FOUND or NOT FOUND for all the crab species you have found.
  37. Remember, you need to take quality evidence photos to prove your claim for each species you have FOUND or NOT FOUND...need some examples of quality data? Look here -
  38. If you did NOT find any crabs in your quadrat, you should still collect data to make a NOT FOUND observation...remember, NOT FOUND is just as important -
  39. Be sure to return any native crabs to their place within your quadrat before heading home.
  40. Important note - If you think you have found a Chinese Mitten Crab - Do NOT return it to the environment. There is a rapid response plan for this species. Freeze it and notify your regional marine resource offices.
  41. There are a variety of ways to deal with green crabs and Asian shore crabs. Some people remove them once they have collected data on them (for composting later on), others mark them so they can see if they re-capture them ( and others eat the invaders (
  42. Once you are back from the field, post your observations to the Vital Signs site.
  43. If you are in Maine: Post your FOUND and/or NOT FOUND observations to the VS database from your “MY Vital Signs” page - Keep the tab open with your published observation, you will need to add this link to the full spreadsheet, here -
  44. If you are outside of Maine: Post your FOUND and/or NOT FOUND observations to the VS Project Bank ( - Keep the tab open with your Project Bank post, you will need to add this link to the full spreadsheet, here -
  45. Use the alternate data publishing format when posting to the project bank. It can be found in the supporting documents on this page -
  46. After you have posted your observations to the Vital Signs site, go to this spreadsheet (
  47. Copy and past rows 2-7 into a new tab
  48. Label this new tab with your school’s/organization's name (or school and class if there will be more than one class contributing)
  49. Go to your tab in the spreadsheet and enter your data

Want to contribute more data?

Elizabeth and Alyson are excited to get any data you can collect in service to this mission, but if you want to dive deeper, bring this Coastal Species Survey & Habitat datasheet ( with you and record these extra pieces of information:

  1. Record water temperature
  2. Record salinity
  3. Record the sex and carapace measurements of each crab found in the quadrat.
  4. Be sure to post this data to the spreadsheet (

Why this mission matters

Both green crabs and Asian shore crabs have been able to thrive in newly established environments because they eat a wide variety of organisms, can stand a wide range of water temperatures, and live in a wide range of salinities (Delaney et al. 2008). In addition to green crabs and Asian shore crabs, scientists and managers are on the look-out for the Chinese mitten crab. This hairy-clawed crustacean was first detected in the east coast in 2005 in Chesapeake Bay and has been found as far north as the Hudson River in New York. It has NOT been detected in Maine or New Hampshire. (

Many scientists, community members, clammers, etc. see the impacts of invasive crabs in their areas, but to understand the long-term impacts there needs to be more data collected. As we see these invasive crabs spreading and disrupting our native ecosystems, many questions have arisen and new ones come up every day. How might these invasive crabs impact our native crab populations?

We hope you will help scientists and managers to try and learn more about where these invasive crabs are and are not, and how many there are. By helping scientists collect these data, we all have a chance to help answer these questions and investigate the impacts of these invasive crabs!

Happy observing and thank you for contributing to this important mission.