OPIHI Equipment: Introduction to Transects and Quadrats

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Adelia Fletcher
6 years ago
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1 OPIHI Equipment: Introduction to Transects and Quadrats OPIHI uses commercially purchased transects. OPIHI uses 12 square PVC quadrats. The quadrats are strung with fishing line to create 2 intersections, 36 equally-sized squares. (See also How to make a Quadrat ). In the following photographs it is difficult to see the fishing line. The line is laid out in a grid as shown in the right diagram.

It does not matter where the quadrat is placed as long as the placement is the same for the entire class.

2 OPIHI Equipment: Quadrat Placement The quadrat is placed at designated points along the transect to get detailed information about a study site. The quadrat should always be placed the same way in relation to the quadrat. It does not matter where the quadrat is placed as long as the placement is the same for the entire class. = Designated Transect Point Transect You can always place the quadrat right over the transect point. Or you can always place the (e.g.bottom right) corner of the quadrat over the transect point.

3 Transects This is a mock study site. The different colored circles represent different organisms. The black line represents the transect. The empty white area will represent sand. The species at this mock site occur in zones, similar to intertidal species. The red are grouped to one side (the way our transect is laid out, this would be towards the shallow intertidal), and the blue are located deeper in the intertidal. Green occur in the middle while yellow occur throughout the site. Transect Point Organism / 1 Blue 2 Sand 3 Sand Yellow Sand With the transect point-intercept method, you only record what is directly under the transect point. Thus, for instance, even though red was very close to transect point #, we still record sand on our data sheet. As you can see, only using transects can miss a lot of information in complex area. We have only recorded two of the four species in this area.

4 Quadrat Point-Intercept Here the squares represent our quadrats. For demonstration purposes, our quadrat only has 9 intercepts and 16 squares. OPIHI quadrats have 2 intercepts and 36 squares. We have chosen to always lay the bottom left corner on the quadrat on the transect point. Quadrat Point-Intercept Method (Numbers designate transect points) Organism/ Red II I Yellow I II Blue IIIIIII Green Sand IIIIIIII II IIIII IIIIIII Total Since there are nine intercepts, the total in each column should add up to nine. You can see that the quadrat point-intercept method has allowed us to record three of the four species at this site, but we are still missing green on our data sheets as it is so small it has never occurred under an intercept.

5 Quadrat Percent Cover In the quadrat percent cover method, you are looking at the total area inside the PVC at once, and thus do not need to pay attention to the fishing line squares. We have found that it is easier to start with the rare organisms/substrate and finish with the most common, in this case we subtracted the total species percentage from 100 to get the percentage of sand. Quadrat Percent Cover Method (Numbers designate transect points) Organism/ Red Yellow 10 8 Blue 8 Green <1 <1 2 Sand Total The total percent in each column should add up to 100. Note that species that occur in less than 1% of the area are not considered in the total. This method captures all the species in our mock study site, but there is a large degree of error because of are estimating.

6 Quadrat Percent Cover Squares Method Because the percent cover method is prone to such a large degree of error, many OPIHI teacher use this variation, called the squares percent cover method. Students are less intimidated as they are looking at a smaller area of the quadrat at a time. In this method, you imagine all the organisms of one species pushed into a corner of the quadrat and estimate how many squares they would take up. Quadrat Percent Cover Method Squares Method (Numbers designate transect points) Organism/ Red Yellow. 1. Blue Green <.2 <.2.2 Sand Total The total number of squares in our quadrat is 16, therefore our columns should add to16. Note that organisms that take up less than 0.2 squares are not included in the total. Later on during data analysis, you can convert the squares into percentages.

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