Learning about Invertebrate Life, One Pinch at a Time

Before entering university, I would never have guessed that terrorizing tiny crabs would be an activity in a Biology lab. Last Wednesday, our lab group did exactly that. We had the opportunity to take a mini field trip right in the backyard of UBC down to Tower Beach for some exploration. We were geared for the adventure with buckets in hand and rain boots on feet.

The goal of our adventure was to explore the diversity of invertebrate life during the low tide, with the following questions in mind: Is there a difference in species richness on top of and under the rocks? Are there more crabs found under large rocks in comparison to small rocks? Are more grazers found on rocks with rockweed (fucus) than rocks without rockweed?

Given the three questions above, our lab separated into groups of 4-5 and embarked on our adventure of terrorizing the tiny crabs. Upon first look, the rocks seem to house only a few animals; such as the barnacles and seaweed. However, when we took a closer look, we found a variety of different organisms tucked away within seaweed and under the rocks. To name a few, we found snails, mussels, scuds and isopods, with the occasional sand flea.

Staying on task, we focused on exploring the three questions at hand; the first being the species richness on top and under the rocks. We began by counting the types of invertebrates found on each boulder. To our surprise, many boulders had a few to zero invertebrates on top. But when we flipped the rocks over, that is where we found an abundance of crabs and the other animals listed above. This allowed us to further question: why are there more species under the rocks? Could it be to avoid predation? Could it be the moisture level? These questions would be great for exploration in new studies.

Our second question was: are there more crabs found under large rocks in comparison to small rocks? That’s when things got exciting. Each of us took on a task to make sure we count all the quick little crabs before they duck away. On the picture attached, you can see one of the little crabs on our hand, getting a personal photo shoot before meeting his friends in our collection bucket.

Tiny crab being held by our giant alien hands. In the background; its friends awaiting for his arrival.

Tiny crab being held by our giant alien hands. In the background; its friends awaiting for his arrival.

Lastly, we focused on comparing the number of grazers on rocks with different amounts of rockweed. We placed a small square at random to mark the area for data collection and counted away. It an interesting trend to observe as we found that the further we moved from the water, the less numbers of grazers we found in the transect.

Although the reasons for our observations may still remain a mystery, it can be said with confidence that our adventure at Tower Beach was one of the best experiences in any biology lab ever!

For some interesting videos of crabs on the internet, take a look at the links below!

National Geographic Channel: the great marathon of red crabs


For an oddly entertaining video of a crab molting (skip to 0:45 for the action):



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