Royal Netherlands Institute for Sea Research
Phone number
+31 (0)222 36 9505
Senior Scientist
  • Marine ecology & ecological parasitology
  • Impact of species invasions and climate change
  • Biodiversity and disease risk
  • Parasite biogeography and macroecology
  • Ecology of the Wadden Sea

Prof. Dr. David Thieltges

Senior Scientist

Parasites are an important part of biodiversity

David Thieltges is an ecologist investigating the role of parasites in ecosystems. ‘Parasites are still a relatively new research area for ecology. For a long time, the prevailing dogma was that parasites would not play a major role in ecology, but that view has now been abandoned. Obviously, parasites have direct effects on species. That was very clear, for example, during the outbreaks of the seal virus and with the high mortality of eider ducks at the turn of the century. Those ducks were found to be infected by a parasitic worm. In addition, parasites can cause more subtle and indirect effects. For example, if shellfish are affected by a parasite and are weakened or perish, this also has an effect on an entire ecosystem. Shellfish-eating birds then have less to eat, but those weakened shellfish also filter fewer algae from the water, which in turn has consequences for the rest of the system.’

Male crabs behave like females

‘Sometimes, the effects of parasites are quite bizarre. Male crabs that suffer from the parasitic crab hacker barnacle start to behave like egg-bearing females. They descend into deeper areas and fan water over the parasite on their belly as if it were an egg sac.’

More parasites indicate more diversity

‘Parasites are usually strongly dependent on specific hosts. A high diversity of parasites is therefore usually associated with a high biodiversity in general. So, in contrast to (veterinary) medicine, “many parasites” are therefore good news in ecology. Parasites only give rise to problems if the general diversity becomes too low. That knowledge has already been translated into new methods for fish farming. For example, salmon are no longer reared in a monoculture but in combination with other species that can keep the parasites at bay.’

‘In another part of my work, I examine the effects of climate change and species invasions on parasites. Due to southern species such as the seabass shifting northwards in relation to warming waters, or because we introduce exotic species ourselves, such as the Pacific oyster, new parasites are also entering our environment and can influence our ecosystems.’

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Research interests

I am a marine ecologist with a soft spot for parasites. My research revolves around understanding the ecological role of parasites in marine ecosystems on various spatial and organizational scales.

Using lab and field experimental approaches, my research group studies the effects of parasites on marine host individuals, populations and communities. We are also interested in how parasites influence the topology and dynamics of food webs. Another line of research aims to understand the patterns and processes underlying infections of marine hosts. This includes work on the role of ambient biodiversity in affecting parasite transmission and disease risk as well as studies on the effects of global changes such as rising temperatures and biological invasions on marine parasites and their hosts. Finally, we study large-scale patterns of parasitism using literature-based datasets and biogeographical and macroecologial approaches in order to understand the forces that have shaped parasitism in the sea.



Since 2020: Honorary Professor 'Marine Parasite Ecology', University of Groningen (NL)

Since 2015: Lecturer in the Marine Biology MSc programme of the University of Groningen (NL)

Since 2014: Senior research scientist at NIOZ Royal Netherlands Institute of Sea Research (NL)

2010-2014: Research scientist at NIOZ Royal Netherlands Institute of Sea Research (NL)

2007-2010: DFG Postdoc fellowship at the University of Otago (NZ)

2006/2007: DAAD Postdoc fellowship at the Aarhus University (DK)



Please find a complete list of my NIOZ publications at the bottom of this webpage or on Web of Science. You can download pdfs of my publications on ResearchGate. I also have a Google Scholar and a Twitter account.

Please note:

Book chapter on 'Ecological Consequences of Parasite Invasions' in new book on Parasites and Biological Invasions by Jamie Bojko, Alison M Dunn,  April M H Blakeslee (2023)

New book on cockle parasites and diseases: de Montaudouin et al. (2021) Catalogue of parasites and diseases of the common cockle Cerastoderma edule. 

Opinion piece on effects of invasive species in the Wadden Sea (in Dutch, 2020) in Friesch Dagblad.

Book chapter in Beninger (ed.) Mudflat Ecology (2018): Thieltges, Mouritsen, Poulin (2018) Ecology of parasites in mudflat ecosystems. Click here for a pdf.

Special issue published in 2016 based on an international NIOZ–AWI symposium held on Texel NL from 10–14 March 2014: ‘Ecology and evolution of marine parasites and diseases’. Co-edited together with Mathias Wegner (AWI, D).

Trilateral (DK, D, NL) report describing and evaluating the current ecological status of the Wadden Sea: Wadden Sea Quality Status Report 2017. Contribution of thematic report and as member of Editorial Board.

Covered by others

Our work covered in WadWeten, a publication series on research in the Wadden Sea  from the Waddenacademie and the Leeuwarder Courant (in Dutch)


Our work covered in the press, radio and science blogs

General ecological role of parasites in ecosystems: Volkskrant

New invasive shell boring worm (Polydora websteri) in the Wadden Sea: TrouwEarthCom, ScinexxPZC, Leeuwarder Courant, NHNieuws, Vismagazine, Fischmagazin, Texelplaza

Virus predation by marine organisms: NRC, ScientiasOceanbites,, NewsweekJapan

Impact of Pacific oyster invasion on parasites and pathogens: DeVolkskrant, OmropFryslan (interview with Anouk Goedknegt, in Dutch)

Parasites in food webs: Parasite EcologyThe Stochastic Scientist, DownToEarth


Professional education

2018: BKO/UTQ (Basiskwalificatie Onderwijs/University Teaching Qualification), University of Groningen (NL)

2012-2013: Management Development Training, Leeuwendaal Instituut (NL) 

2006: PhD in Ecology (summa cum laude), Christian Albrechts University Kiel & Alfred Wegener Institute for Polar and Marine Research, Wadden Sea Station Sylt (D)

1993-2001: MSc/Diplom in Biology (summa cum laude), major in zoology/ecology and minors in conservation biology, evolution & systematics and philosophy, Philipps University Marburg (D)

1996/97: Visiting student for an academic year (ecology, evolution, palaeontology and history of science), University of Edinburgh, Scotland


Awards and Prizes

2023 29th Petersen Excellence Professorship, Kiel (D)

2007: DFG Postdoc fellowship for a three years stay at the University of Otago (NZ)

2006: DAAD Postdoc fellowship for a 9 months stay at Aarhus University (DK)


Research Group

Cyril Hammoud - Postdoc. Project  'Assessing the spatial-temporal status and long-term trends of European fish parasite biodiversity' as part of EU Biodiversa+ project IMPACT Integrated Monitoring of Parasites in Changing Environments. In collaboration with Rachel Paterson (NINA, Norway) and Juan Antonio Balbuena (University of Valencia, Spain) and the IMPACT consortium. 

Ana Born Torrijos - Postdoc. Marie Curie project 'Compound specific stable isotope analysis as a novel tool to unravel parasitic trophic interactions–PARAISO'. In collaboration with Philip Riekenberg & Marcel van der Meer (NIOZ) and Bernd Sures & Milen Nachev (University Duisburg-Essen, Germany).

Rosa Jolma - PhD candidate. Project 'Infectious diseases in a changing world: combining experimental data with eco-epidemiological models to understand the dynamics of parasite invasions under climate change'.  In collaboration with Hans Heesterbeek (UU, NL) Mathias Wegner (AWI Sylt, DE), and Anieke van Leeuwen (NIOZ).

Haiyan He - PhD candidate. Project ‘Disease ecology and predation: unravelling consumptive and non-consumptive effects of predators on parasite-host interactions and population-level consequences’. In collaboration with Anieke van Leeuwen (NIOZ)

Lénia da Fonseca Alexandre Rato - PhD student (co-supervised). Project 'An integrated approach to unravel the adaptation potential and environmental plasticity of native and non-native crab species'. MARE - IPLeiria (Portugal), main supervisor:  Marco Lemos (MARE IPLeiria).

Max Willems - MSc student. Project 'Invasion of the shell-boring worm Polydora websteri in the Netherlands". University of Amstderdam (NL). In collaboration with AWI Sylt (D), NIOZ Yerseke and Hoogeschool Zeeland (NL) 

Former PhD students

Maral Khosravi (2023, co-supervised). Project 'Interactive impact of thermal stress and parasitism on gastropods in an extreme and variable sea environment, the Persian Gulf'. GEOMAR & Kiel University(D), main supervisor and promotor: Martin Wahl (GEOMAR, D).

Qian Huang (2021-22). Project 'Ecology of Hematodinium infections in crustaceans'.  Visiting student from the Joint PhD Training Program of the University of Chinese Academy of Sciences (UCAS).

Annika Cornelius (2021, co-supervised). Project 'Interspecific interactions and ecosystem effects of invasive mud crabs'. AWI Sylt & Bremen University (D), main supervisor: Christian Buschbaum (AWI Sylt, D); promotor: Kai Bischof (University Bremen, D).

Jennifer Welsh (2020). Project 'Biodiversity and disease risk in marine ecosystems'. In collaboration with Corina Brussaard (NIOZ), promotor: Jaap van der Meer (NIOZ, VU).

Claudia Bommarito (2020, co-supervised). Project 'Global warming effects on host-parasite interactions in common molluscs of the Adriatic and Baltic Sea'. GEOMAR & Kiel University (D); main supervisor and promotor: Martin Wahl (GEOMAR, D).

Anouk Goedknegt (2017) Project 'Pacific oysters and parasites: species invasions and their impact on parasite-host interactions', defense at the Free University Amsterdam (NL), promotor: Jaap van der Meer  

Former MSc students

Former MSc students Wouter Koch (RUG Groningen, NL), Tabea Stier (University Hohenheim, D), Marieke Feis (RUG Groningen, NL), Reinier Nauta (RUG Groningen, NL), Jarco Havermans (RUG Groningen, NL), Anne Karin Schuster (University of Landau, D), Marin van Regteren (RUG Groningen, NL), Caroline Liddell (Wageningen University, NL), Annabelle Dairain (Pierre et Marie Curie College Parais, F), David Shoesmith (RUG Groningen, NL), Boukje Heidstra (RUG Groningen, NL), Sarah Bedolfe (RUG Groningen, NL), Eeke Haanstra (RUG Groningen, NL), Romy Cartiere (University of Amsterdam, NL), Luca Prins (University of Wageningen, NL), Lotte Geerlings (University of Wageningen, NL), Tjibbe Stelwagen (RUG Groningen, NL), Mark Bouwmeester (RUG Groningen, NL), Tijs Joling (University of Amsterdam, NL), Joshua Dagoy (University of the Basque Country, E), Jeffrey Knol (RUG Groningen, NL), Tom van Splunter (Leiden University, NL), Nadine Bleile (RUG Groningen, NL), Rebecca MacKinnon (Utrecht University, NL), Yente Kuperus (Radboud University Nijmegen, NL), 

Former interns & visitors

Anke Hempel (D), Mirjana Markovic (D), Estefania Velilla (NL), Karlos Ribeiro de Moraes (BR), Wiem Boussellaa (PhD student; Sfax University, Tunisia), David Bello Jimenez (University of Malaga, E), Nadine Bleile (University of Freiburg, D), Svenja Kling (Heidelberg University, D), Mariken van den Heuvel (HAS Den Bosch, NL).

MSc projects

Various research projects for MSc students are available all year round. They range from field studies over field and lab experiments to literature-based  approaches. Please contact me for more details or check the NIOZ internship webpages.


I am curently teaching in courses in the Marine Biology MSc (and BSc) programme of the University of Groningen.

In addition, I teach in the NIOZ Marine Masters Summer Course

Linked news

Monday 06 November 2023
David Thieltges receives the 29th Petersen Excellence Professorship
With his work in the field of marine parasite ecology, NIOZ researcher David Thieltges provides important insights into the functioning of marine ecosystems and ocean health. In honour of his contributions, the Prof. Dr. Werner Petersen Foundation…
Monday 11 September 2023
'A crab is never just a crab'
A herring in the North Sea, a crab in the Wadden Sea or an anemone fish on a coral reef, ... biologists like to think in terms of individual species that all have their own place within food webs in ecosystems across the world. "But that is surely…
Monday 19 June 2023
June 16-25, Week of Invasive Species: 'Invasive species can also add something to nature'
Plants or animals brought into nature - accidentally or on purpose - from distant lands can cause major problems. Such exotic species, especially when they are also "invasive," pushing out native species, are therefore seen in a negative light. But…
Friday 20 August 2021
Marine parasites secretly nibble from their hosts
Parasitic copepods that were thought to use their marine hosts as a foothold and to steal food from their intestinal tract, now turn out to use a mixed feeding style to feed on both the host and its food. By applying a novel molecular method to…
Thursday 29 October 2020
David Thieltges appointed honorary professor Marine Parasite Ecology
David Thieltges has been appointed honorary professor of Marine Parasite Ecology at the University of Groningen. As an ecologist, David Thieltges (NIOZ and UG), has a long track record of studying the role of parasites in ecosystems. He is looking…
Thursday 06 August 2020
First record of invasive shell-boring worm in the Wadden Sea means trouble for oyster
In October 2014, the suspicion arose that the parasite worm Polydora websteri had found its way to the Wadden Sea. Following years of research, that suspicion has now been confirmed: the worm, that likely originates from the Asian Pacific, has…
Thursday 26 March 2020
Animals keep viruses in the sea in balance
A variety of sea animals can take up virus particles while filtering seawater for oxygen and food. Sponges are particularly efficient. That was written by marine ecologist Jennifer Welsh from NIOZ this week, in a publication in Scientific Reports.…
Thursday 01 February 2018
Wadden Sea World Heritage launched Wadden Sea Quality Status Report 2017
The new Wadden Sea Quality Status Report (QSR) is now available. Over the course of two years, more than 100 scientists have reviewed and evaluated the current ecological status of the entire Wadden Sea based on a trilateral monitoring programme…
Friday 27 October 2017
Exotische Japanse oester vriend en vijand van Waddenzeebewoners
Exoten vormen wereldwijd een bedreiging voor mariene ecosystemen. Deze invasieve soorten die door menselijk handelen (aquacultuur, scheepsvracht) in een nieuw gebied komen, gaan de strijd aan met inheemse soorten: ze vreten ze op of overwoekeren…

NIOZ publications

Linked projects

Effects of invasive species
David Thieltges
Netherlands Organization for Scientific Research - Ocean and Coastal Research
Project duration
31 Dec 2011 - 30 Aug 2020