Ontogenetic Shift in Diet of Unicornfish

Introduction

After a few months of transportation, food, and gear planning, I travelled to Lizard Island and stayed there for 11 days to complete research for my Master’s Thesis. The location for this research was chosen based on the availability of the species and the fact that my advisor, Dr. Andrew Hoey, was familiar with the area. The species I’m examining, Naso brevirostris, are more common around the island. However, what’s the reason I’m investigating the diet of these species, and why is it important or interesting?

My project is investigating the ontogenetic shift in the feeding behavior and diet of the Palefin Unicornfish, Naso brevirostris, a common Indo-Pacific reef fish. This species undergoes a dietary shift from herbivory to planktivory, a transition that is presumed to take place when these fishes reach approximately 20 centimeters in total length. However, this size threshold remains poorly supported by quantitative data. By integrating gut content analysis and feeding observations, this research aims to identify a more precise estimate of the size range in which this transition occurs. This approach will enhance the understanding of the ecological roles and trophic interactions of this species, highlighting the significance of ontogenetic diet shifts within coral reef systems

Photo of Palfrey and South Island during sunrise. Found south of Lizard Island

Life in the Field

Each morning started around 7-8 am. We ate breakfast and loaded snorkel and diving gear onto the boat. We travelled to different locations around and away from Lizard Island for abundance, surveys, field observations, and collecting samples. After arriving at a reef, we would put our gear on and focus on the objective at hand, most often it was collecting samples as that was the most difficult replicates to obtain. The days were filled with swimming and moving around to different locations. The large amount of biodiversity and scenery surrounding the island and different reefs never made the trips dull, only exciting. I saw so many things I’d never seen before: large groupers, numerous reef sharks, turtles, dolphins, and much more!

Aside from the large biodiversity and sights, I was very surprised at how difficult spearfishing would be. Collecting samples this way was challenging as you had to be patient and persistent. On the first day of fieldwork, I collected 0 samples, but the next day, I caught roughly 12. I was also surprised by how long it took to dissect and analyze the fish samples we collected after bringing them back to the research station. There were many hours spent after coming back at around 3-5 pm that we spent analyzing or dissecting fish. 

As time passed on the island, it became very natural. The process got easier, and I felt that I learned a lot. When the time came to pack up and go, I was sad to leave but felt fulfilled. In a way, I completed a chapter in my research career and was looking forward to working on writing my thesis. I’ll never forget the experiences I had and everything I learned at Lizard Island. 

Challenges and Highlights

While I knew fieldwork wasn’t always as glamorous, it certainly can be a lot of work. On my first day of field work, I wasn’t able to catch a single fish from spearfishing as it was my first time. However, the next day, I got 12! Similar stuff happened where I struggled learning a new method of analysis or fieldwork but improved over time. Overall, my biggest challenges were getting over the learning curves. This led me to become more experienced and have a new set of skills for the future. Fortunately, there were no technical, weather, or safety issues during fieldwork!

Photograph taken along the eastern shore of Lizard Island, near the research station. The vessel is known as Kristy K, this was the vessel my team used for research.

What I Learned

Doing this fieldwork at Lizard Island felt very different as it was focused on my project. In this way, it was very exciting but also sometimes stressful. Overall, it allowed me to gain new experiences despite the many learning curves that came with the trip. I also learned the many challenges/positives of field research. This experience helped me appreciate my advisors even more as they were indispensable during the project and provided much insight. Patience, persistence, and a big smile are some of the key things I believe are necessary when doing field research, as it is hard work but an experience that should be enjoyed.

Acknowledgements

Huge thanks to Andrew Hoey, Victor Huertas Martin, Bec Piper, and Kieran Martin for their assistance in the field. I’m very grateful to be able to work with them and gain new experiences during my time at Lizard Island. Also, a huge thanks to the Lizard Island Research Station and to all of the staff that work there. They were very kind and accommodating during my time at the research station.