LTREB Intertidal Oregon State University
Started April 2011 Updated January 2016
This work was done to determine size of individual disturbances and total proportion of the mussel beds disturbed in the mid-zone over time.
Replicates per Site: 5 Mussel Beds
Materials: Two 50 meter transect tapes, camera with underwater case, blue 15 cm ruler, Mussel disturbance notebook, two mussel bed depth rods, hammers, mussel bed depth datasheet
Setup in Field:
In the each of the five designated mussel beds (see site maps) the total area of the bed must be measured. The best way to do this, since most mussel beds are not perfect ovals, is to:
1) As accurately as possible create a map of the mussel bed.
2) Measure the length of the bed (L) at the longest point, leaving the transect tape laid out, recording the distance on your map.
3) Measure the widths at 5-10 meter intervals, recording the distance of the widths (x) on each side of the length transect tape and where the widths (y) cross the length transect tape on your map. (see diagram below)
Mussel Bed Disturbances:
After you have the total area of the mussel bed measured each disturbance in the bed needs to be measured. A disturbance is an area where the mussels have been ripped off recently, there is bare rock showing, and byssal threads attached to the rock. An area where barnacles have been ripped off the rock with bare rock left behind is also considered a disturbance. The area of each disturbance needs to be measured. The best way to do this is to determine the shape of the disturbance. Most disturbances can be considered ovals and only two measurements are needed; length and width. However, some disturbances are triangles and three measurements are needed; the three sides of the triangle. Some have disturbances have very odd shapes and as many measurements as are needed to accurately describe the disturbance should be taken. A photograph should be taken of each disturbance using a ruler as a proxy for distance. More than one picture may be required to capture the entire disturbance.
Mussel Bed Edges:
For each of the 5 designated mussel beds at each site, 100 mussel bed depth measurements are needed. The 100 measurements should be evenly distributed across the bed. For beds longer than 25 meters, 50 measurements every half meter along the main transect line laid down for mussel disturbances and 50 measurements spread through the rest of the bed works. For smaller beds be careful not to measure the same spot twice. At each spot using the hammer drive the mussel bed rod until you are confident the rod has hit bare rock below the bed. Then record the measurement on the mussel bed rod to the nearest centimeter. These measurements work most efficiently with two people hammering the mussel bed rods and one person recording.
These measurements need to be done each year in the spring.
Once back in the lab, photographs should be relabeled (ex. 4_2; with the mussel bed number first and disturbance number second) and put photographs into a new folder with the corresponding to the site and date in the LTREB folder under the Mussel Disturbances project.
Processing: The area of each mussel bed needs to be calculated. To do this the mussel bed should be recreated to scale in Photoshop using the map and measurements made in the field. Then using Image J the overall area of the mussel bed and the individual disturbances can be calculated. All the numbers should be compiled on the spreadsheet found here in the mussel disturbance folder