KFE BIOE 161Habitat associations – Swath Surveys
Assessing patterns of habitat association – Swath Surveys
Last week we used uniform point contact surveys to sample a set of species and the physical habitat on which they occurred. The species sampled were primarily those that either were not readily countable (because of their growth form or because they occur as aggregations) or were so small and numerous that counting was infeasible. The relative abundance of such species is typically assessed by sampling their percent cover and one method to do this is by the use of uniform point contact surveys. For those species that are countable we often use some form of quadrat sampling, where quadrats are placed in in an unbiased fashion and then selected species are counted in within the quadrats. We will use this approach in this lab. Here the quadrats are large and we are calling them swaths, but the goal is the same – we want to count the number of individual of selected species in each swath. Each swath will be 30 by 2 meters wide and will be subdivided into 5 meter (by 1 meter) sections (see below). Consult the data sheet to see what species will be sampled. Occasionally species will be so abundant that it would take too long to count all individuals. We use the following rule to account for this possibility: If you get to 15 individuals within a 5 meter subdivision, note where you are in the 5 meter section (eg 3.5 meters) and stop counting. For example if between 10 and 15 meters you encounter 15 Cystoseira by the 11.5 meter mark, you would enter “15 at 1.5 meters”.
Approach
Each buddy pair will be the same as in the UPC surveys. In addition each pair will be assigned the same meter mark on the cable. The goal is to have you sample the exact same transect as you did for the UPC surveys. The first dive will be to the deep side of the cable. Each group will lay out a 30 m transect at 90 degrees. When you complete sampling, reel in the tape, leave it on the cable and come to the mooring to complete a safety stop. After the safety stop come to the boat, jump up on the boat and swap your bottle. Return to the cable and use the same protocol on the shallow side of the cable (270 degrees). When you are done, reel up your tape and either return to the boat (first making a safety stop) or kick in to shore using the return trip as your safety stop. We will instruct you as to which approach to use prior to going in the water.
Linking the two surveys
By sampling the same transects as were sampled using UPC methods we will be able to link the results of the two surveys. Specifically we will be able to determine if habitat characteristics are associated with the distribution of countable species (those sampled in swaths). Here though habitat characteristics will include both physical and biological attributes. So for example we will be able to determine if the density of Pisaster is related to substrate type, relief and UPC species cover. We will do this by calculating for each 5 meter section of the transect (from the UPC surveys)
1)Percent of substrate that is sand, bedrock, cobble or boulder
2)Percent of area that has 0-10cm, 10cm -1m, 1m-2m, >2m relief
3)Percent of area that is of each species sampled (eg lacy red algae)
These three habitat attributes can then be compared to the counts of organisms sampled in the swath surveys.
Key questions:
1)Are swath species associated with habitat features?
2)Which type of feature (biological or physical) is most predictive for each swath species
3)Are there particular patterns of association?
- For example, are some swath species particularly related to a UPC species
Key safety points - remember these
1)You need to check in prior to going in the water
2)You should never ascend to the surface with less than 500 PSI
3)Make your safety stops
4)You should check your air and your buddy’s air before you go into the water and then again immediately upon descent. Many problems, which are not detectable at the surface maybe more apparent at depth. For example, a poorly opened valve may not restrict air until you are at depth.
5)Check your buddy’s air at least once (midpoint) during each dive.
6)If for some reason you have less air than you should when you start your ascent, make a safety stop anyway and monitor your air so that you don’t run out. Let one of us know that you are coming up with a low tank.
7)Never exceed 50’
8)If you realize that you are low on air, leave your tape in place, ascend to the boat and let one of us know that you left the tape and indicate the meter mark on the cable. We will retrieve it.
9)Always let us know if anything unusual occurred on the dive – for example rapid ascents, any pain or headache, any injuries, any distorted vision or ear pain,you saw a large shark swim by, etc.
10)All other diving rules are in place
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