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Careers in Science 

October 16, 2008

Conducting Science – Sand Crab Monitoring

Beginning in 2004, the intern program has worked with the Gulf of the Farallones National Marine Sanctuary and their LiMPETS program (Long-term Monitoring Program and Experiential Training for Students) over the summer to collect Pacific mole crabs (Emerita analoga), otherwise known as sand crabs, at Ocean Beach.

Pacific mole crab, aka sand crab

Pacific mole crab, aka sand crab

The two main reasons we participate in this monitoring program are:

We collect and monitor the sand crabs because they are an important link in beach ecosystems; they are prey for shore birds, fish and sea otters. More importantly, sand crabs are intermediate hosts to Acanthocephalan parasites. If the sand crab is infested with parasites and then is consumed by a bird, fish or sea otter, then this new host becomes infected as well, which can lead to death.

The parasite in the body of the sand crab

The parasite in the body of the sand crab

Interns get hands-on experience in performing real research, such as collecting and dissecting specimens as well as data entry.

 Samples are collected once a week between June and August from the same area on Ocean Beach. We take ten samples from five random transects in this area. If the Interns find any sand crabs, we record the sex and length. After we finish, we pick fifteen sand crabs of varying size and sex to bring back and dissect.

Surveying the scene at Ocean Beach

Surveying the scene at Ocean Beach

Collecting a sample

Collecting a sample

Examining the sand crab

While we are dissecting the sand crabs, we record information such as the size, sex of the crab, where and when it was collected, and how many parasites are found. When we finish dissecting the sand crabs, we send the data to the Gulf of the Farallones National Marine Sanctuary. They receive data from many other volunteer and school groups. This helps the researchers see the bigger picture and observe long-term changes and trends.

Dissecting the sand crab

Dissecting the sand crab

Filed under: Conducting Science — CiS Interns @ 1:32 pm


  1. my father, little borther and i found alot of these crabs.
    They look like they have been breading well.
    Close to Kalbarri, Western A ustralia, Australia.

    Comment by Andrew Scally — May 29, 2011 @ 12:45 am

  2. We also found a few with a heap of eggs.

    Comment by Andrew Scally — May 29, 2011 @ 12:47 am

  3. Hi Andrew Scally here, just letting you know my father, little brother and i were fishing one day and found a bunch of these here mole crabs, it looks like the have been breeding very well.
    Close to Kalbarri, Western Australia, Australia.

    Comment by Andrew Scally — June 6, 2011 @ 8:45 pm

  4. How do you determine the sex of a sand crab?

    Comment by Rosie — July 5, 2011 @ 8:37 am

  5. cool

    Comment by john smith — November 15, 2011 @ 8:53 am

  6. We found alot of these crabs in seaside new jersey

    Comment by Ashley — June 3, 2012 @ 5:45 pm

  7. i found alot also. near westhamptom beach and sag harbor.

    Comment by Sarah — June 29, 2012 @ 3:50 pm

  8. i see the shore birds getting these, are they in the water or below the sand? … either way, do you know what is living below the sand as i see tiny holes in the wet sand that look like air holes?


    Comment by kim — August 24, 2012 @ 10:15 pm

  9. I am interested in doing something similar on the New Jersey coast. Can you tell me what the core sampler is made of, how you get it down into the sand, and how you get it out with the core intact? Thanks, in advance.

    Comment by Ralph Boerner — December 7, 2012 @ 8:43 am

  10. Hello Ralph, thank you for your comment. Our core sample is made of PVC piping. You can find more information on how to create your own equipment on the LiMPETS: Sandy Beach Monitoring website. Here is the link: http://limpetsmonitoring.org/sb_equip.php

    We push down the PVC piping into the sand, use our hands to stop the sand from flowing out, and gently let the sand pour out into a sifter. We use a little bit of ocean water to help sift the sand away, which leaves only our specimens. The core doesn’t really stay intact because we pour it into a sifter.

    Comment by ciseditor — December 28, 2012 @ 11:17 am

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