Trish Koh: Seaurchin for answers
Kathy: Tell me a little bit about yourself and how you came into doing the Masters project that you’re doing.
Trish: I’ve always had an interest in the natural world. I started off in engineering, but after two years of my degree, I realised that it wasn’t really for me. I switched my major and moved into zoology and it’s been a lot better for me. It’s something I find more engaging and allows me to pursue a passion for getting out there and wondering why animals are where they are.
Kathy: What is your masters project about?
Trish: I worked on a native pest species of sea urchin (Heliocidaris erythrogramma) in Port Phillip Bay. It’s one the sea urchins that is responsible for something that’s called a sea urchin barren, where a region that would have previously been populated by kelp is completely decimated by too many hungry sea urchins. I looked at trying to understand this problem better by researching how sea urchin larvae (their babies) disperse through the seascape.
Kathy: What was the first aspect of your research focused on?
Trish: The first thing I looked at was sea urchin larvae swimming metrics, which means I looked at their swimming capacity and how much they’re capable of moving through the water. A lot of people think about how water movement transports larvae horizontally on the surface of the ocean, but I looked at their vertical movement. The ocean is a pretty complex 3-D body. There’s surface layers going one way, but water can be moving in a completely different direction many layers below the surface. It’s important to determine if different larvae can navigate which layer of water they’re in. With a lot of species like sea urchins, their adults stage don’t move around very much, so their larvae will determine their location.
Kathy: What were the results from the first part of your experiment?
Trish: I’ve established what sea urchin larvae are capable of doing across different stages of their larval form. I looked at sea urchin larvae for about eight days each. On day one, they’re usually in the egg stage, and over time they grow through different stages (early stage larvae, later stage larvae, and metamorphosed larvae). What I found was when they’re in the egg stage, they’re very buoyant. But when they hatch, they move a little bit faster upwards. When they metamorphose, they are quite neutrally buoyant and then they suddenly start actively swimming downwards when they’re older.
Kathy: So what does the second part of your research project look at?
Trish: After determining the swimming capacity and migration in the first part of my project, the second part integrates all the data I collected into a model. We use a dispersal model which releases simulated particles that represent larvae to see where they end up. You can pinpoint which areas they will go towards based on which areas (or patches) they were born. What you can do with something like this is make a connectivity network. Connectivity networks can be used to look at spatial communities. So using connectivity theory, we can work out which patches are more closely linked and which patches aren’t.
H. erythrogramma larva under the microscope. Video by Trish Koh.
Kathy: So what are the management implications of your research?
Trish: Using the connectivity network, we can determine which patches provide a lot of sea urchin larvae to different populations. If the population really needs one area to really survive because that’s where they get all their larvae, we could get rid of this patch to help decrease the sea urchin population within Port Phillip Bay. We can work out thing such as the importance of particular patches to the overall population dynamics of the bay by looking at these connectivity networks.
Kathy: How is this different to what the management of this species of sea urchin is like right now?
Trish: Management is mainly focused on adults. What groups like Parks Victoria have done previously is gone out to a certain region and taken out up to 57,500 sea urchins. When something like this is done, the adult sea urchin population in an area is eradicated but we don’t know how long that lasts for. The supply of larvae to a region is also really important, as it helps sea urchin larvae to recruit an area and help establish a new population.
Kathy: We’re almost handing in our thesis, what are you plans after you finish your masters?
Trish: I’m not too sure yet. I might try and do some more research on sea urchin biology. I might also explore science communication a bit more. I really like the idea of talking to people about science, and I’m currently working in the Science Gallery, which is a gallery where science and art collides. It targets 15-25 year olds to try and get them more interested in science, and I’ve been working there and really enjoying it.