Using a quadrat-based survey method to perform an ecologial survey of a roacky coastline.
Rocky shores are environments in the littoral zone (the area between the highest high tide line and the lowest low tide line) are a great place to study marine animals, as they have rich biodiversity and interesting marine life.
Rocky shores are made of large boulders and a rocky substrate, and are widespread throughout the world, however these techniques work on all shorelines, and quadrat surveying is also common on land and in scuba/snorkelling surveys underwater.
Despite being easily accessible to study, rocky shores are extreme environments which organisms are highly adapted to, having to deal with fluctuating water levels, salinity, temperature, sun exposure and exposure to predators. Coastal zonation, the different assemblages of animals and seaweeds at different heights in the littoral zone, as shown in figure 1, is a famous feature on rocky shores and is a great phenomenon to study with quadrat surveys. Where an animal or seaweed is found on a rocky shore is subject to their adaptations and competition between organisms.
In the infralittoral zone, which is only exposed at the lowest low tides which occur twice monthly at spring tides, you find organisms which cannot survive for long periods when exposed to air and sunlight, however there is strong competition here. Red seaweeds are found here, as they can photosynthesise in deeper waters, due to their photosynthetic pigments which make them red. In the midlittoral zone, organisms have medium exposure, and medium competition, and as they can photosynthesise below the surface, brown algae are mostly found here. In the supralittoral fringe, you find organisms which can be exposed to air, high temperatures, predation, and extremes of salinity for long periods, and may only be submerged once or twice per day. Many organisms in the upper littoral zone have adaptations to retain water, such as anemones or seaweeds which curl to hold water, such as Channel Wrack (Pelvetia canaliculata). The very top of the supralittoral fringe zone is only submerged once or twice a month, during spring tides, so is usually dominated by lichens, which can survive being submerged occasionally but have evolved to live on land.
Quadrat surveys on the rocky intertidal zone can be used to produce very important data. You may choose to study a single rocky shore over a longer period to see how it is changing or survey several contrasting shores in short succession to see how their conditions impact marine life. You could also combine these approaches and study several contrasting shores over a longer period.
When developing your hypothesis, ask yourself questions such as:
Once you have decided what you will study, the next step is to make a prediction (a.k.a develop your hypothesis). This might be that climate change is causing seaweeds to move down the shore, or that seaweed helps animals survive on rocky shores by hiding them from predators.
Your final step is to design your study. Will you repeatedly return to the same shore to see how it is changing, or will you compare different types of shores (for example, surveying 3 heavily polluted shores and 3 less polluted shores)? How will you control for other factors, to make sure that the variable you are studying is actually causing the effect? For example, if comparing polluted and unpolluted shores, maybe the difference is because the polluted shores are near river outflows (and therefore have lower salinity), whilst the unpolluted shores are further from rivers? You could control for this factor by making sure all your unpolluted shores have similar salinity. There are many other factors to consider, such as timing and logistics, how many repeats transects you will do and how you will analyse your data.
A quadrat (figure 2) is a basic tool- in its simplest form it is a square (usually 50cm*50cm). You can make these by nailing wood together, or by attaching PVC pipes together with pipe corners. These can be upgraded by creating a grid of equally spaced wire or string, making it easier to count animals and calculate percentage cover.
Measuring tapes are useful for placing your quadrats, and a camera is very useful to later verify data, and to calculate percentage cover later. Correctly identifying species, especially those which look similar, such as barnacles and seaweeds, is important, so research common species beforehand or take a shore guide and take pictures of anything you are unsure of to identify later. Instruments such as temperature, salinity and PH probes allow for the collection of important environmental variables, however, are not necessary for all studies.
The simplest way to set up your quadrat survey is to choose a random transect (straight line) from the water line to the supralittoral fringe and move along the transect at intervals of 1/10 of the transect length, or at set intervals (e.g., 2m). At each of these intervals, place down your quadrat and start counting the organisms the square. For most animals, such as barnacles, anemones, and periwinkles, you count individuals. For seaweeds, we calculate percentage cover; how much of the quadrat that seaweed covers, which is where a grid of wires becomes useful. Make sure to look under seaweeds to count all the organisms and be aware that if there are multiple species of seaweeds overlapping with each other, total percentage cover may exceed 100%.
You should do at least 2-3 transects per shore, and additionally, if you are comparing conditions (e.g., exposed vs sheltered, polluted vs unpolluted), you should survey at least 2-3 of each type of shore to prevent pseudo replication. By replicating, we are ensuring that our findings are not due to random differences on different shores/parts of the same shore, but rather a pattern found in shores of these conditions.
There are many ways to analyse your data for these studies, and you can analyse your data in simple programs like excel, or more advanced programs such as R, MATLAB, or Python.
If your study involves comparing conditions, a histogram or bar graph of counts/percentage cover may be useful in your analysis. Figure 3 is a histogram I made from rocky shore data in R.
The rocky shore can be a dangerous environment, especially when you are focused on doing science. It is important to be aware of your environment to stay safe, for example, keep an eye on the tide to make sure you do not get stranded on the high shore. To prevent falling, wear shoes with good grip, and always keep your hands out of your pockets to catch yourself if you do fall. These surveys are more fun and safer when you have someone with you, and make sure to tell someone what you are doing in case something happens.
How to carry out a rocky shore quadrat transect survey: ROCKY SHORE TRANSECT SURVEY METHOD (otago.ac.nz)
ID guide of common UK rocky shore species: Microsoft Word - Rocky shore ID guide.doc (ncl.ac.uk)
Methods and ID guides for UK/Ireland rocky shore species The Shore Thing (mba.ac.uk)
Methods to determine salinity: Methods of Determination of Salinity – SalinometryMethods of Determination of Salinity – Salinometry
Ballantine, W. J. (1961). A biologically-defined exposure scale for the comparative description of rocky shores. London: Field studies council.
Cefali, M. E., Cebrian, E., Chappuis, E., Terradas, M., Mariani, S., & Ballesteros, E. (2019). Community-dependent variability in species composition and richness on rocky shores at a regional scale. Esturine, Coastal and Shelf Science, 230, 106425.
Chappuis, E., Terradas, M., Cefali, M. E., Mariani, S., & Ballesteros, E. (2014). Vertical zonation is the main distribution pattern of littoralassemblages on rocky shores at a regional scale. Esturine, Coastal and Shelf Science, 147, 113-122.
Gaspar, R., Pereira, L., & Neto, J. M. (2017). Intertidal zonation and latitudinal gradients on macroalgal assemblages: Species, functional groups and thallus morphology approaches. Ecological Indicators, 81, 90-103.
Stephenson, A., & Stephenson, T. A. (1949). The universal features of zonation between tide-marks on rocky coasts. Journal of Ecology, 37(2), 289-305.
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