An Afternoon Amongst the Intertidal Residents of Tower Beach

If you were at Tower Beach, last Wednesday afternoon, then you probably saw a group of UBC students in the intertidal zone carrying large white buckets, squares of green metal, and measuring tapes. You would have also seen these students trying to fit large boulders into the small green squares. Then, when they failed to do so, they would flip the boulders over in anger. Finally, (because they didn’t look crazy enough already) you would have seen them scramble to sink their hands into the sand beneath the boulder in order to throw some mysterious objects into the large white buckets. After performing the above routine on one boulder they would find another one and do it all again.


The intertidal zone is where the organisms were found that we used in our comparisons. Source:

Okay, so as normal as this all seems, you’re probably still wondering what they were actually doing. Well, as one of those crazy looking students, I can tell you that we were collecting data in order to make comparisons and practice using different statistical tests.

One comparison that we were looking at was whether there were more grazers under rockweed or out in the open. This is where the green squares come into play! We placed them on each boulder and counted the number of snails and limpets found within that area. By using the squares we were able to keep a standard area when collecting data across boulders of varying sizes. This in turn allowed us to look at the effect of rockweed on the number of individuals and not the effect of boulder size.


Students counting the number of species underneath a boulder

Another burning, yearning and pressing question that we attempted to answer was whether or not there were different numbers of species on top vs. underneath the boulders on the beach. We made this comparison by first counting the number of species on top of the boulder. The most common organisms we found were mussels, barnacles, isopods, rockweed, snails and limpets. We then proceeded to flip the boulder over and count the number of species underneath it. The most common organisms on the underside were shore crabs, snails, mussels, limpets and polychaetes. After returning to class and looking at the data from this comparison, we found that there were approximately the same numbers of species on the top and the bottom of the boulders. Does this make sense? If we think about what we were initially comparing then it does! In our comparison, we were looking at the number of species found and not the similarity of species found on the top and the bottom. Although the top and bottom had similar numbers of species, the top had a lot more rockweed, snails, limpets and mussels whereas the bottom was predominately shore crabs and polychaete worms. In the future, it would be interesting to look further into why/how the two sides are composed of such different species while still maintaining the same number of species.

So there you have it, although weird things can happen at Tower Beach, we were just a group of students making science happen! I’m sure from afar our data collecting looked pretty strange, but it all makes sense now, right? Data collection is all about being as objective and accurate as possible. That being said, if carrying around a few odd looking gadgets is the only cost for that then bring on green squares and measuring tapes!

If you are unfamiliar with any of the organisms discussed above then check out the link below! BC Parks has a great brochure with information on some of the various local intertidal species.


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