Jenni Stanley, a PhD student at the Auckland University Leigh Marine Laboratory, explains why she does field work as well as laboratory-based studies. She discusses some of the limitations of working in a laboratory setting and how she does research in the field.
At the moment, I’m looking at how ambient levels of reef sound affect the larval behaviour of crabs. To investigate my research question, I do a series of lab experiments and a series of field experiments.
For my lab-based experiments, I have four different treatments. Each treatment is contained in three tanks, and within the tanks, you will have a speaker playing sound through the water. All the treatments represent different kinds of habitats, and I expose crabs to the sounds from those habitats. What I watch for are behavioural and physiological changes in the crab larvae, so I look for reduced swimming activity. After the settlement, I look for physiological changes, so I see whether the crab has moulted into the next juvenile stage.
I decided to conduct field studies as well as laboratory-based studies because you have a lot of lab-based artefacts. When you are dealing with sound, it is quite difficult to control sound waves in a very small tank. Because I am actually broadcasting it from a speaker, you won’t get exactly the right kind of composition from an underwater speaker as you would from a natural source of sound, so you know, a little speaker will not produce the low-frequency sounds that you’d get from a reef.
So in the field, I chose three different habitat types. I chose an open sandy beach called Pākiri Beach – that is a local beach – Waterfall Reef – a macroalgae-dominated rocky reef – and Whangateau Harbour – a sandy shelly-bottomed harbour. So within those three habitat types, I tethered small Perspex frames to the seabed, and within those frames, I held 30 individually house megalopae, so crab larvae, and I looked at the changes in behaviour.
In the field-based experiments, I had very similar results to the lab-based. They showed a strong affinity to the macroalgae-dominated rocky reef, which is a perfect habitat as adult crabs. These crabs that I used are specifically matched to this kind of habitat
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