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?

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 is also incomplete. We need more hands on deck to monitor our coastlines and truly dig into what effects these marine invaders may be having on our environment.

Mission Steps

1. Decide on your field site location (a rocky intertidal zone near you) look up when low tide occurs.

2. Print the Coastal Species Survey datasheet. Because you will be documenting 5 species, you will need to print 3 extra copies of the last page of the datasheet (if you are working as a team, then each teammate will take on one of the species instead of one person looking for all 5).

3. Print these species ID cards:

4. Make a prediction. 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 in the field notes section of your datasheet (follow the link to the full teacher instructions at the bottom of this page for more detail around this step).

5. Gather your fieldwork equipment and head out into the field (at low tide) to search for native and invasive crabs!


6. Follow the random quadrat sampling method protocol (here) to determine where to place your quadrat.

7. Go through your quadrat, looking under rocks and seaweed, to search for any crabs that may be hiding within your quadrat. When you find a crab, place it in one bucket (with water in it) to sort later.

8. Go through the crabs in your bucket. Use your crab identification skills (and the species ID cards) to gather data to support a claim that you found or did not find the species in question. Fill in your Vital Signs datasheet while you are collecting photo and written evidence to make your claim of found or not found for the species you were looking for (if you were searching for more than one, you'll need multiple datasheets). See the link to the full teacher instructions at the bottom of this page if you need more detail on fieldwork equipment and the protocol to use in the field.

9. After you have found all the crabs that are in your quadrat, note the total number of crabs that you found in the field notes section of your Vital Signs datasheet.

10. Now sort your crabs into buckets, using one bucket for each of the different species you find. Use your Vital Signs ID cards to help you identify which crab species you have. 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.

11. Be sure to return any native crabs to their homes before you leave the field (NOTE: if you find a Chinese mitten crab, do NOT release it! Follow the instructions listed on the species ID card for this species. See the full teacher instructions for ideas on how to deal with green and Asian shore crabs).

12. Post your observations...

  • If you are in Maine:
    • Post your found and/or not found observations to the VS database from your “MY Vital Signs” page. Check out these "How-to Guides" if you need help posting data to the site. Keep the tab open with your Project Bank post, you will need add this link to the full spreadsheet.
  • If you are in New Hampshire:
    • Post your found and/or not found observations to the VS Project Bank. *Use the "Alternate Data Publishing Format" found HERE when posting to the project bank. Keep the tab open with your Project Bank post, you will need to add this link to the full spreadsheet.

13. In Maine or New Hampshire, after you have posted your observations to the Vital Signs site, go to this spreadsheet

  • Copy and paste rows 2-7 into a new tab
  • Label this new tab with your school’s/organization's name (or school and class if there will be more than one class contributing)
  • Go to your tab in the spreadsheet and enter your data

14. Celebrate! Go further: take a look at what other schools have found, create a pie chart that shows the percentage of native versus green versus Asian shore crabs, what do you think your data is telling you?

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. Water temperature
  2. Salinity
  3. Sex and carapace measurements of each crab found in the quadrat.
  4. Be sure to post this data to the spreadsheet mentioned in step 13.

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 NH (Smithsonian Environmental Research Center - Marine Invasions Research Lab).

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.

**See the full teacher instructions HERE**