Back in BC

We arrived back in Bamfield for our summer field season. Actually, most of the crew has been here for over a week and already worked through a tide series putting out the dynamometers we worked so hard to calibrate over Thanksgiving. The rest of the crew, including me, arrived last Thursday.

Today was my first day back in the field, and while I don't enjoy the alarm going off at 4:00AM, the beauty of the area more than makes up for it. Jenny and I went to look for mussels that we had tagged last summer. You would think that an organism that glues itself down would be pretty easy to find year after year, but mussels move around much more than they are given credit for as "sessile" animals. Luckily they don't usually move that far, so if we tag a mussel and accurately record the its position we have a pretty good chance of finding it again ... assuming it hasn't been swept away in a storm.

We've noticed that in the middle of very thick beds, small clumps of mussels (about a foot wide) will start to protrude out of the otherwise level mussel bed. We call these clumps "hummocks." We've been curious as to whether mussels in these hummocks are more likely to get ripped off of the bed by storm waves than those in the flatter, more uniform portion. In a way, these hummocks might unintentionally protect the bed as a whole, by letting some mussels get ripped away, but leaving the rest of the bed intact. 

To try and test the hypothesis that mussels in hummocks are more likely to be lost than those in the "flat" part of the bed, we tagged 40 mussels at one of our field sites, 20 in hummocks and the other in flat area. We tag them by etching a letter into the shell with a dremel, putting superglue in the groove, then blowing chalk dust on the mussel. It's a mess when you are doing it, but in the end you can get a nice durable tag.

We also put a small notch in the shell to measure growth. Mussels grow from the end you see pointing up (technically, it's the rear-end of the mussel, even though it's the end pointing up out of the bed). The notch leaves a little scar in the shell, and its distance to the edge of the mussel indicates growth.

To record position, we measured the distance to each mussel from two fixed points on shore with transect lines (=very long measuring tape). It's a nice, low tech method that is surprisingly accurate. We also took measurements with surveying equipment to put the data into a GIS system. However, the measuring tape method lets us find the mussels without having to haul out the survey equipment.

After all that, we were excited to find mussels again after a year. Of the 20 mussels in the flat area, we found eight. We found none of the hummock mussels. In some cases, we could clearly see where hummock has been ripped of the bed (but the mussels underneath were still there). It's encouraging data, but we'll keep checking over the summer to be as sure as possible we've found all the tagged mussels we can.