My eyes squinted in the bright September sunlight as we walked out of the forest onto Tower Beach, thankful to not be spending the afternoon sitting at a desk. Any excuse to spend a few hours in ‘class’ splashing around the intertidal zone, flipping over rocks, catching crabs and working on the spectacular farmers tan I’ve developed over the summer, and I’m a happy man! However, our group wasn’t just here to play around and try to avoid eye contact with the local nude beachgoers; we were here to use statistics to explore some interesting questions of species distributions on and under the rocks.
Have you ever lost sleep at night wondering if there are different numbers of species on top of a boulder compared to underneath, if grazer species are more abundant in areas with rockweed, or if size and numbers of crab can be explained by boulder size they are under!? No? …well, me neither, but last wednesday we set out to explore these questions!
We got the crab in the bucket.
Learn more about the intertidal zone: https://www.crd.bc.ca/education/in-your-community/ecosystems/coastal-marine/intertidal-zone
First off, we began to count the number of species on the tops of randomly selected boulders which we measured for size. On top, we found such species as limpets, barnacles, mussels, snails and isopods, which judging by the way they arched their backs ready to fight, were not happy with being pulled from their kelp home. After counting, we prepared to flip each boulder over to catch and count as many scuttling crabs as possible. After collecting as many as we could, where I tried not to scream like a little girl each time one was able to pinch one of my fingers, we counted the number of species on the bottom of the boulders. Here, we saw new species such as polychaete worms burrowing into the sand and amphipods swimming in the water, which were counted before each rock was returned to its position. Lastly, we looked at small quadrat sections on top of the boulders to see if there were more grazer species such as limpets and snails in areas with the rockweed, fucus, compared to boulders without fucus. Finally came the sad realization that we were going to have to head back to the lab, so we began walking back up the long staircase to campus where I tried to maintain conversations while trying to catch my breath and hide how out of shape I am
Once back in the biodiversity building, we used the power of sitting back and watching Dr. Chris Harley do statistics with our data. Our results showed that there was no significant difference in numbers of species underneath versus on top of rocks, and that there was no difference in herbivore numbers in areas of fucus compared to those without, which was a surprise to me. We did, however, find a significant relationship whereby more crabs are generally found under larger rocks.
Overall, not a bad way to spend the afternoon.