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Last week I went out to collect the data for my field project. Low tide was particularly low – between 0 and 0.5m – and I had three days without rain. On Tuesday I did site a, on Wednesday site b, and on Friday I did sites c and d. At each site I did 10 replicates. It took me 10-20 minutes to generate, diagram & plan movement between the 10 co-ordinates, and sampling took between 19-58 minutes at each site (varying depending on how many oysters I was finding: site d only took 19 minutes, but 6 of the 10 samples had no oysters).
The sampling design worked fairly well. Once I placed the 1m x 1m markers, I looked for oysters, and for each oyster I added a tally mark to the “T” (for total) column, and then tallies for its position relative to the rocks. After collecting data at site b, I made the table where I recorded the tallies larger, because a couple of samples at site b had so many oysters that the tally marks didn’t fit entirely in one box. I also made a note to clarify that the “N” column, for oysters not in any rock shadow, includes oysters that are on top of or attached to the front of rocks. Oysters that are on top of a rock, but in the shadow of some part of the rock, are not included in the N column but in the relevant L, R, or B columns.
I think I may have to exclude sample 8 at site c, because that sample had 2 large rocks that were absolutely covered in oysters, to the point that that sample had 50 more oysters than any other sample. Because the rocks were covered, many oysters were behind other oysters, not behind any rocks. I recorded the ones behind other oysters in the “B” column because they are in the shadow of something breaking the wave action, but in hindsight I have no way of knowing which oysters came first, so some of the ones that are currently behind oysters may have not been earlier in their growth. For these reasons I think sample 8 can be disregarded.
Interestingly, an ancillary pattern seems to be that the difference between B and N is not large, but there are many fewer oysters found left or right than are found behind or not in shadow. I wonder if there might be something advantageous to the oysters to being towards wave action that only kicks in if the oyster is fully exposed – this might explain why there are many oysters behind rocks and not at all protected by rocks, but not slightly protected on either side. Or maybe there’s some aspect of fluid dynamics that means the water movement at the sides of rocks is worse than not near rocks.
