• Sunset view of Glacier Bay and the surrounding Fairweather Mountains.

    Glacier Bay

    National Park & Preserve Alaska

Activity #2 Dungeness Crabs at Home in Glacier Bay

 

Teaching Note:
For students who need help reading the resources used in this activity, you may read it with them, distribute copies of the Crab Glossary, and/or form guided reading groups.

 
Dungeness Crabs

Dungeness Crabs sheet

1. Read: Dungeness Crabs at Home
Divide the Web sites listed under Crabs in Resources among the student groups. Distribute Dungeness Crabs and allow students to work together in small groups to read about the movements and habitats of Glacier Bay's Dungeness crabs. Then, discuss:

  • What is the range of water depths in which Dungeness crabs can be found?
    Answer: .5 meters – 180 meters
  • In what months of the year are adult crabs most likely to bury themselves in large groups in the sandy/silty bottom of the water ocean floor?
    Answer: winter months: November through early spring
  • How might you explain this?
    Answer: probably to survive the winter storms and strong currents
  • What regular event coincides with the crab larvae hatching?
    Answer: phytoplankton bloom
  • Why is this good timing for the baby crabs to hatch?
    Answer: plenty of food available for the newly hatched larvae
  • How do researchers explain the phenomenon of male and female adult crabs gathering together in groups or aggregates?
    Answer: Females gather in groups during the winter months while they incubate their eggs. Males may group in a kind of schooling phenomenon to gain protection from predators. Also, the depressions or trenches in which they group and that provide protection from predators, are rare.
  • How do the crab larvae "get around"?
    Answer: They drift on the currents.
  • What about the last larva stage, the megalops? How does it travel?
    Answer: Megalops are relatively strong swimmers.
  • What do Dungeness crabs typically eat?
    Answer: Dungeness crabs are foragers. They scavenge the sea bottom for organisms such as shrimp, mussels, small crabs, clams and worms.
  • In what two marine environments can adult, juvenile or larval Dungeness crabs be found?
    Answer: intertidal and subtidal
 

2. Student Resources: The Intertidal Zone and The Subtidal Zones and the Ocean

Divide the following resources among three student groups:

NPS Glacier Bay – Intertidal and Subtidal Zones
http://www.nps.gov/glba/naturescience/intertidal-subtidal.htm

NPS Glacier Bay – Intertidal and Subtidal Photo Gallery
http://www.nps.gov/glba/naturescience/intertidal-subtidal.htm?eid=206819&root_aId=123#e_206819

NPS Glacier Bay – Nature and Oceans
http://www.nps.gov/glba/naturescience/oceans.htm

Teaching Note: If appropriate, subdivide the student groups into smaller reading groups to help them as they read about these three important Glacier Bay environments that Dungeness crabs call home.

When the students have completed their reading, discuss:

  1. How would they describe a crab's eye view of each habitat?
  2. What other creatures would live there?
  3. What sensory (sight, sound, touch, etc.) experiences might be characteristic of each zone?

Answer: Answers will vary with students' imaginations, but information should be verifiable from their reading.

 

3. Create a Web page for Glacier Bay

  • After the students have completed their reading, ask them to discuss the information on Dungeness Crabs. Does the Glacier Bay site have a page of information on their Dungeness crab population?
  • Give the students time to explore the Glacier Bay Web site to look for any information they can find on these crabs. Instruct them to organize any sites they find as "readable" by the general public or "readable" by scientists.
  • Divide students into small groups. Challenge them to create the Web page or PowerPoint slide show on the Dungeness Crabs of Glacier Bay that they believe would enhance the Glacier Bay site.
  • Instruct them to include on their site:
    • What crabs eat at each stage of their development
    • How crabs cope with environmental conditions and changes, predators, and scavenging
    • What the crabs' favored environment is in Glacier Bay at each stage of their development
    • What resources they will cite on their presentation or Web page
  • Share these in a bulletin board display.

4. Extension

Invite interested students to research the Internet or the local library to find pictures of each of the marine ecosystems they read about. They could then design an information poster or bulletin board, called A Crab's World, showing the different habitats of a crab through its lifetime. The artwork should be as accurate as possible and contain as many of the known denizens of these zones. Students can then annotate A Crab's World, sharing information about the ecosystems they are depicting and the crab's life stage and role(s).



5. Resources

Habitat Choices

NPS Glacier Bay – Intertidal and Subtidal Zones
http://www.nps.gov/glba/naturescience/intertidal-subtidal.htm

NPS Glacier Bay – Intertidal and Subtidal Photo Gallery
http://www.nps.gov/glba/naturescience/intertidal-subtidal.htm?eid=206819&root_aId=123#e_206819

NPS Glacier Bay – The Intertidal Life of Bartlett Cove
http://www.nps.gov/glba/naturescience/intertidal-subtidal.htm?eid=206819&root_aId=123#e_206819

NPS Glacier Bay – Nature and Oceans
http://www.nps.gov/glba/naturescience/oceans.htm

ADF&G Wildlife Notebook – Dungeness Crab
http://www.adfg.state.ak.us/pubs/notebook/shellfsh/dungie.php

Fisheries and Oceans Canada – Dungeness Crabs
http://www.dfo-mpo.gc.ca/zone/underwater_sous-marin/crab-crabe/crab_e.pdf

Washington Department of Fish and Wildlife – Crabs
http://wdfw.wa.gov/fish/shelfish/beachreg/4clam.htm

ADF&G Sport Fish – Estuarine Environment (Rocky Intertidal and Mudflats and Beach)
http://www.amscopub.com/images/file/File_140.pdf

Dungeness Crabs

Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (Pacific Southwest) pages 4-8 on Life History
http://www.nwrc.usgs.gov/wdb/pub/species_profiles/82_11-063.pdf

The Dungeness Crab http://www.dungeness.com/crab/

Dungeness Crab (Wikipedia)
http://en.wikipedia.org/wiki/Dungeness_crab

Dungeness Crab
http://www.psmfc.org/habitat/edu_crab_fact.html

 

go to Activity #3 >>>
Economic Significance of a Crab Refuge

Did You Know?

Mt Fairweather

Captain James Cook named the tallest mountain in Glacier Bay, Mount Fairweather, in 1778. As Southeast Alaska is a temperate rainforest, with an average of only 50 sunny days a year, it would require fair-weather to see that mountain.