Scientific Methods: Transects

A transect is a straight line of a chosen distance along which observations or measurements are taken which ‘represent’ the conditions of an environment. Researchers will map out a transect, often with physical markers (I used star pickets) and a tape measure and then randomly or selectively sample ‘variables’ along this line. Variables might include the number or size of each organism in the quadrat, the sediment size, presence of water or other material such as litter. Observations are made by placing a quadrat (square) along the transect and making observations about what you see inside. This method is useful for making observations in areas with an uneven distribution of populations (such as plant or animal species) and it’s quite cheap. I made my quadrat from four lengths of PVC pipe, each 0.5 m in length, with corner connections.

For my research, I was most interested in understanding if the seagrass ecosystems in certain areas had changed since previous studies had been conducted, ultimately to validate existing datasets. Ahead of time I selected locations for the transects based on existing seagrass maps. In the field, I collected data at seven different locations which had three transects in each. I used a random number generator on my phone to select 10 locations along the transect to place the quadrat. Once the quadrat was on the ground, I recorded the seagrass species, the percent cover of the species (100% cover would mean I could only see seagrass and 0% means there is none), sediment type, algae and any other important variables to consider.

What can we learn from transects?

Data collection is important to monitor the health of ecosystems. Repeating the same transects over periods of time (seasonally or annually for instance) allows us to observe changes in the environment. If changes are observed, we can call on external datasets to begin to infer what may have caused these changes, so we can monitor more variables in the future. For example, if seagrass in a particular area, continued to decline (the percent cover kept decreasing), we might want to start monitoring water quality in the area to see if increased turbidity or excess nutrients in the water are contributing to the decline.

Ultimately, the more data we have, the easier it is to monitor the health of ecosystems and intervene if degradation begins to occur.

Lessons-learned from my first transect:

  • Working in the inter-tidal zone, you need to account for tides, so make sure you walk with the tides i.e. walking seaward as the tide is going out
  • Taking photos is difficult at midday because the sun reflects on the water, which as you can see from my photos is everywhere
  • Walk on only one side of the transect so you don’t put footprints in any of the quadrats
  • Pockets! In the inter-tidal area, you can’t rest your equipment or personal items anywhere without them getting wet or muddy so zip-up pockets are a must!
  • Don’t wear a white sun shirt to do field work in mud

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