Posted on 12 November 2020
Interview with: Leonardo Durante
Originally from São Paulo, Brazil, University of Otago PhD student Leonardo Durante recently submitted his thesis, funded through the Ecosystem connectivity project. His thesis comprises an in-depth analysis of the changing trophic structure of New Zealand’s commercially fished species. He has recently published two papers relevant to implementation of ecosystem-based management.
In this interview, Leonardo explains his research into the food webs of past and present fish, and how a sea slug inspired him to learn more about life under the sea.
How did you get interested in marine science?
The first time I went for a snorkel in the ocean as a kid, the water was so murky I couldn’t see anything – not even my hands in front of me. Then suddenly I saw an Aplysia [a giant sea slug that swims by moving its arms)] coming towards my face. And I was like, whoa! I freaked out. That sea slug showed me just how much I didn't know about the world under the sea. In high school, I wanted to do electrical engineering but then I realised I needed to be in the ocean to be happy. So, I decided to do oceanography.
How did you get involved in the Ecosystem connectivity project?
In 2014, I came to Otago University on an exchange program for a year, which I loved. I did some fisheries and marine ecology with Steve Wing [Ecosystem connectivity project leader]. Ecology really caught my attention - it’s super cool how organisms interact with the environment.
I went back home to finish my undergrad degree at the University of São Paulo, where I worked on the bycatch of marine mammals and modelling coral habitats in the Atlantic Ocean. When I finished, I messaged Steve about doing postgrad in Dunedin, and he replied with an invitation to work on his recently funded Ecosystem connectivity project.
What problem you were trying to solve with your project?
Humans have been fishing fish for so long – but we know surprisingly little about them and their histories. I looked at 16 species of fish and wanted to know: What were their food web ecologies like in the past? How has their abundance has changed? How have the interactions between them and their environment changed? Is there any difference today, or has it always been like this?
The fish species Leonardo studied were: leatherjacket, blue cod, gurnard, elephant fish, common warehouse barracuda, tarakihi, spiny dogfish, giant stargazer, red cod, sea perch, lockdown dory, hoki, hapuka, ling, orange roughy.
A pretty big topic! How did you approach it?
We were essentially trying to compare today’s environment and fish with the environment and fish from a hundred years ago. But since we can’t time travel, we had to figure out how to get information about the past. Te Papa and Otago Museum have so many collections of fish species, all in jars. Some were fished up a hundred years ago, preserved in ethanol and never been touched since. It's amazing.
But getting the information we needed wasn’t going to be easy, because the fish had been altered by the chemical fixation and preservation.
Isotope analysis detects the signature of an isotope – a chemical element such as carbon – showing how it has changed over time since fossil fuel use and industrialisation began. Just like climate scientists can use ice or mud core samples to measure the changes in CO2 levels in the atmosphere, I used this approach in the preserved fish.
This ‘carbon signature’ is found the cells of primary producers like phytoplankton and kelp. Because fish eat primary producers, and those fish are eaten by other fish, we can track the carbon signature through the food chain. And this information tells us about their diets and how things have changed.
Luckily, we were able to extract good enough ecological information from the muscle tissues of the ‘patients’ [the 100-year old fish in the jars] to compare them to present-day fish.
What did you learn?
Firstly, that we could see this change using this kind of data [isotopic], no one had done it before. We showed that isotopic variability due to fixation and preservation were dependent on variables other than time under preservation, which we could correct mathematically
Secondly, now we know that food web is changing and has been changing since the 1930s. We’re seeing increasing abundance for coastal species like barracuda, spiny dog fish, gold sharks. But for popular species like red cod and tarakihi, we saw a decrease in abundance over time. Their diets have changed too – they’re eating more of the pelagic [open ocean] species than the coastal, inshore species.
These changes are ecological responses to complex variables and interactions between them, like climate, fisheries, and abundance and distribution of important prey species. The takeaway message is that things are changing, species are using less resources from the coast and this is probably related to human activities.
Now that you've finished your PhD, what’s next?
I’m working for Steve to the end of January on some other projects. I've published two papers from my thesis so far, I have one under review, and I'm preparing two more.
But I'm going to be moving to Adelaide, Australia soon because my wife has a scholarship to do her PhD in marine science there. We're supposed to be there already, but because of coronavirus we're stuck here. So, I'm on the hunt for a job in Australia next year.
What do you love the most about the ocean?
When you are in the ocean, especially under the water it’s very, very peaceful and you can relax. I like to free dive all the way to the bottom, lie down and then look up at the water above. For me it’s one of the best feelings in the world. It’s kind of funny to say that and then do research showing all the problems in the ocean. Unfortunately, I haven't done much of that this year because I sold most of my gear because I thought we were leaving the country!
Find out more about Leonardo’s research
- Durante LM, MP Beentjes and SR Wing. (2020). Shifting trophic architecture of marine fisheries in New Zealand: Implications for guiding effective ecosystem‐based management Fish and Fisheries 21: 813-830
- Durante LM, AJM Sabadel, RD Frew, T Ingram, and SR Wing. (2020). Effects of fixatives on stable isotopes of fish muscle tissue: implications for trophic studies on preserved specimens Ecological Applications