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My second field observation took place on the 20th of February, from 15:05 to 16:30, at multiple sites in the intertidal zone along the stretch of beach north of Volunteer Park. The weather was overcast and lightly spitting (it started raining more fully right after I finished), and approximately 7 degrees. High tide had been predicted at 10:34 (4m), and low tide was predicted for 18:34 (1.6m).
I initially wanted to compare oysters & mussels along the gradient from the top of the beach towards the water’s edge, by recording the number & size of all the oysters and mussels found in three spots from the beach’s edge to the water’s edge. I quickly realized after I started to make observations that the number of mussels, their sizes (ranging from 5mm to 90mm) and their close proximity to each other and attachments to various surfaces made this initial plan impractical. I decided to focus my observations on oysters instead, but because there were fewer oysters, I thought just three observations sites along the gradient might not be sufficient.
Ultimately I chose three locations along the beach – one at the stairs from Volunteer beach, the other two approx. 40-60m to the west and east of the stairs – and, starting right at the edge of the beach, I walked in a line towards the water. With each pace, I turned around and counted the number of oysters visible in the space between myself and where I had stood at the previous pace, within about 1 metre to either side (see the rough diagram in red, in the photos of my field journal). Each count was recorded in one square in my field journal, and I paced and counted until I ran out of space on the page. As I counted, I noticed that there seemed to be more oysters where there were big rocks (greater than ~30cm) than more “clear” areas, so I noted where there seemed to be more rocks as I was counting. In the third location, counting was hampered by the presence of seaweed/algae/general mud & slime that covered lots of the rocks and surface.
I want to focus on the distribution of the oysters, comparing areas with large rocks to areas without.
Possible processes that might cause the distribution difference:
- large rocks provide more shelter, so in areas without shelter, the oysters are more likely to be predated upon by birds and therefore fewer would be found there
- obviously since some of the oysters are not unattached, a large rock provides more surface area for oysters to attach, so more would be found there
- possibly confounding factor: more attached oysters by big rocks might be competing for resources with unattached oysters, so more unattached oysters might be in places without large rocks
I hypothesize that the shelter provided by large rocks will cause more oysters to stay nearby. My prediction is that I will count more oysters, attached and unattached, very close to large rocks than I will count where there are no large rocks.
The predictor variable would be the presence of a large rock, which I would not control so it would be a natural, not a manipulated experiment. It is categorical, because it is either the presence or absence of large rocks. The response variable would be the number of oysters, which is a categorical variable, because it is a count of how many there are (contrast with if it was a measure of how big they grow, which would be continuous).
Your research project sounds very interesting. Your prediction that you will find more oysters around large rocks is clear. The presence of large rocks and number of oysters should be easily measurable in the field as they are counts. I wonder if there would be any seasonality to long term data? Could the presence of warmer weather affect where the oysters are found (IE hot sun and risk of drying out?) or are different bird species found predating on them at different times of the year.