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Thomas Swierts

Thomas Swierts, PhD candidate - Marine Biodiversity


Email: thomas.swierts@naturalis.nl
Phone: -
Room number: Vondellaan 55, Leiden
“Dive into the sea and you cannot help but admire the diversity you see.”

I remember the endless hours on summer days that I spent as a boy looking for bugs in our garden. I remember the weekends in winter when I chose to stay inside the house watching nature documentaries being mesmerized by the voice of Sir David Attenborough. I remember being awe-struck when my uncle told me about his diving adventures around the globe. Life was fascinating and I wanted to know everything about it. It was no surprise that I decided to study Biology, I was surprised by so many things I learned. Life is fascinating and I still want to know everything about it. 


The first time I came to Naturalis was in December 2011. I had just started with the master’s program Limnology and Oceanography in Amsterdam and wanted to talk to Dr. Nicole de Voogd about sponges and internship opportunities. She explained me her work and told me about an expedition to Indonesia for which she could use an extra pair of hands. I was sold and seized the opportunity: I went to Indonesia! There I was impressed by the work of all the other Naturalis researchers that joined the expedition, and by the beauty of the underwater world around Lembeh Island, but most of all by the sponge I was working on. They were so impressive! I am two meters tall, so I am not used to meeting many people taller than me, let alone a sponge. But I stumbled upon a few true giants, easily over two and a half meters tall. No wonder it is called the giant barrel sponge.

The internship was a great success and my results were later published. During the next part of my studies I always kept thinking about ‘my’ giant barrel sponges and everywhere I went diving I tried to collect a few samples. After I finished my master’s in 2014 I told her Dr. Nicole de Voogd that I would be very interested in working for her. The first good news came in 2015 when she received a grant and I could start doing some work, but the best news came last summer when she got her VIDI-grant. So at the end of 2016, after almost 5 years since my first introduction to a giant barrel sponge, I am finally officially a PhD student working on giant barrel sponges at Naturalis! 


Research interest

My work focuses on Giant Barrel Sponges, mainly in the fields of:

- Population genetics

- Taxonomy

- Distribution

- Ecological funtioning

- Microbial communities


Current research topics


Dr. Daniel Cleary ( University of Aveiro, Portugal)

- Dr. Mark Vermeij (Carmabi Research Institute, Curacao)



Supervision of Master students

- Nisma Abdelmalik (2017) Competition between corals and turf algae on a shallow reef in Vietnam.

- Roy Belderok (2017) Population genetic structure and reproductive timing of giant barrel sponges in Curacao.

- Megan Clay (2017) Variation and flexibility of microbial communities in giant barrel sponges.

- Gydo Geijer (2017) Competition between corals and turf algae on a shallow reef in Vietnam.

Available student projects




Swierts, T., & Vermeij, M. J. (2016). Competitive interactions between corals and turf algae depend on coral colony form. PeerJ4, e1984.

Setiawan, E., de Voogd, N. J., Swierts, T., Hooper, J. N., Wörheide, G., & Erpenbeck, D. (2016). MtDNA diversity of the Indonesian giant barrel sponge Xestospongia testudinaria (Porifera: Haplosclerida)–implications from partial cytochrome oxidase 1 sequences. Journal of the Marine Biological Association of the United Kingdom96(02), 323-332.




Swierts, T., Peijnenburg, K. T., de Leeuw, C., Cleary, D. F., Hörnlein, C., Setiawan, E., ... & de Voogd, N. J. (2013). Lock, stock and two different barrels: comparing the genetic composition of morphotypes of the Indo-Pacific sponge Xestospongia testudinaria. PloS one8(9), e74396.