Scientific Methods: What is Seagrass Coring?
Coring is a method used to extract anything underground, in this case, seagrass roots. We used PVC pipes that were 16 cm in diameter and place them over a seagrass plant we wanted to extract. Usually in sand and mud you can press firmly on the top of the pipe to force it into the ground. The ground was a bit harder than we realised so we often had to stand on them or hit them with a shovel to really get them into the ground. Once only a few centimeters of the pipe were still visible above the sea bed we had to extract the core. This is the difficult part. We needed to dig to the bottom of the pipe so we could place our hand under it to stop all the sediment from falling out. Digging usually took around 15-30 minutes depending on the density (the firmness) of the the sediment. Once we’d dug deep enough, we placed our hand under the core and very carefully lifted it out of the water.
Why do it?
Taking cores of seagrass allows us to conduct experiments on the plant with all its roots still intact.
The cores taken in the video were of a species called Enhalus acoroides growing in Xincun Bay of Hainan Island in China in 2018. I conducted a series of experiments in a laboratory at Hainan Tropical Ocean University where I investigated how root structure affects erosion. I transplanted the cores into a purpose-built frame designed by the Netherlands Institute of Sea Research (NIOZ) and place the frame into a wave tank. Once the cores were fully submerged, the wave tank generated waves. The design of the frame exposed one side of the seagrass cores, aiming to mimic the conditions of a seagrass cliff. In this way, we could test to see if the seagrass was able to ‘hold onto the sediment’ admist the wave action, or whether it was eroded.
Coastal erosion is increasing globally and so I wanted to investigate the role of seagrass on cliff erosion (small underwater cliffs in the order of 1-10cms). Basically, the results from my experiment suggest that not all species of seagrass are able to reduce erosion equally and that the type of roots and root structure are important for sediment stability. Not all seagrass species offer the same amount of coastal protection.
Photos of the core preparation before placing the cores and frame into the wave tank, a) One seagrass absence core and one seagrass presence core transferred into the core frame; b) Control core (seagrass absent) scraped back to sit flush with the metal plate taped to the front to limit the wave-exposed area to a designated cliff height of 8 cm; c) Schematic of wave tank setup for this experiment developed at the Royal Netherlands Institute for Sea Research (NIOZ); d) Photo of the wave tank set up at Hainan Tropical Ocean University. Differences in the wave damper and wave maker from panel c are highlighted. Frontal erosion setup as in panel c is identical in panel d but not shown in the photograph.
Image and caption from DOI: https://doi.org/10.1016/j.ecss.2021.107316
Measuring the amount of sediment lost after an experiment with cores without seagrass.
Want to know more?
If you’d like to read the full details of the experiments or look at the detailed results, you can find the published article in Estuarine and Coastal Shelf Science here: https://doi.org/10.1016/j.ecss.2021.107316
Enjoyed looking through this, very good stuff, thankyou.