Royal Netherlands Institute for Sea Research
Royal Netherlands
Institute for Sea Research
Phone number
+31 (0)113 57 7320
  • Gelatinous zooplankton (jellyfish) ecology and taxonomy
  • Zooplankton
  • Pelagic ecology of coastal systems
  • Invasive species
  • Fisheries sustainability

Dr. Lodewijk van Walraven


Research interests

I am a marine ecologist passionate about sustainability, biodiversity, taxonomy and how human-induced changes are affecting marine ecosystems. For my PhD in marine ecology I investigated changes in gelatinous zooplankton (jellyfish) communities in Dutch coastal waters by analysing long-term datasets and performing field surveys as well as experiments.

My current research is focusing on understanding the biodiversity and ecosystem functions of zooplankton in food webs of Dutch coastal waters. Zooplankton is an understudied group and using state of the art methods such as underwater microscopic imaging I aim to fill this knowledge gap. At NIOZ EDS I am currently working on testing and implementing NIOZ' new underwater microscope CPICS which uses deep learning image classification to classify planktonic organisms to different taxonomic groups.

Experienced in organising research projects, research cruises and monitoring surveys, analysing long-term data, experiments, and species identification/taxonomy of benthos as well as zooplankton and fish.

Visit my personal website here and my website on zooplankton here.




November 2020 - present:  Marine ecology researcher, Royal Netherlands Institute for Sea Research (NIOZ), Yerseke, testing and implementing imaging techniques for studying zooplankton diversity and their functions in coastal ecosystems.

2017 - present: Freelance consultant, van Walraven Marine Consultancy and freelance photographer,

2016– May 2020: Marine ecology researcher, Royal Netherlands Institute for Sea Research (NIOZ), Texel Investigating the environmental effects of Reverse Electrodialysis power generation (Blue Energy) on the environment and impact of clogging, fouling etc by organisms in the REDstack experimental power plant in the Netherlands.

2015– 2017: Researcher Fisheries, Good Fish Foundation, Veenendaal Development, maintenance and improvement of the VISwijzer website en iOS en Android apps. Performing sustainability assessments for fisheries and aquaculture products for Good Fish Foundation and different clients.

2009–2010: Research assistant, Royal NIOZ, Texel Performing field- and lab work; sampling and identification of zooplankton and benthos in the Wadden Sea. Projects: SIBES (NIOZ/NAM) and PRODUS (Rijkswaterstaat) 2009: MSc research internship, Royal NIOZ, Texel Investigating the species composition and seasonal patterns of gelatinous zooplankton in the Wadden Sea by means of a weekly sampling programme. I also participated in 6 week-long sampling cruises for the NIOZ NWO-ZKO project Structure and trophic functioning of Wadden Sea fish fauna.
Supervisor: Dr. Ir. Henk van der Veer.

2008: Research assistant, University of British Columbia, Olhão, Portugal Assisting Project Seahorse researchers with SCUBA diving fieldwork investigating distribution and ecology of seahorses. Underwater transects, measuring and tagging seahorses in the Ria Formosa nature reserve in southern Portugal. Supervisor: Dr. Iain Caldwell.



Please find my complete list of NIOZ-publications at the bottom of this webpage. You can download all my publications on ResearchGate.


Professional education

2010–2014: PhD, Royal NIOZ, Texel During my PhD I studied the occurrence, species composition, seasonal patterns and long-term changes in populations of gelatinous zooplankton in Dutch coastal waters. Focused on changes following the introduction of the invasive ctenophore Mnemiopsis leidyi. First I qualified and quantified the role gelatinous zooplankton plays in the ecosystems of Dutch coastal waters, primarily the Wadden Sea. The invasive ctenophore Mnemiopsis leidyi was found to be the most abundant species present in the area. Using field sampling, experiments and Dynamic Energy Budget modelling I investigated what makes this species such a successful invader.
Promotor: Prof. Dr. Theunis Piersma, University of Groningen. Co-promotores:
Dr. Ir. Henk van der Veer, NIOZ en Dr. Victor Langenberg, Deltares.

2007–2008: MSc research internship, Wageningen IMARES, IJmuiden Performing a study on fisheries induced evolution in North Sea plaice, more specifically on sexual dimorphism in reproduction and growth. For this project I sampled discards and bycatch of North Sea beam trawlers and joined several ICES IBTS and BTS surveys on the North Sea. I presented the results at the International Flatfish Symposium in Sesimbra, Portugal in 2008. The study is published in Journal of Sea Research.
Supervisor: Prof. Dr. Adriaan Rijnsdorp.


Awards and Prizes


PhD thesis

The study
Whether jellyfish numbers are increasing worldwide is an ongoing debate, but it is a fact that jellyfish-related problems such as clogged fishing gear and cooling water intakes, and tourists avoiding beaches, are increasing. In Dutch coastal waters the introduction of the invasive comb jellyfish Mnemiopsis leidyi triggered a renewed interest in this diverse group of animals. In 2010 I started a study on gelatinous zooplankton in Dutch coastal waters, in a collaboration between the NIOZ Royal Netherlands Institute for Sea Research and Deltares. On November 18, 2016 I defended my thesis at the University of Groningen.


Fifty years of jellyfish catches in a fish fyke on Texel show that jellyfish are appearing earlier in the year following warmer winters. The number of jellyfish caught had decreased. Polyps (bottom-living stages of jellyfish) were also studied and searched for on the bottom, on wrecks and in harbours and ports. Only polyps of the moon jellyfish were found. Knowledge of the distribution of polyps can lead to better forecasting of jellyfish problems in the future.

The American comb jellyfish is now the most common gelatinous species in Dutch waters. Experiments showed that the species can survive in very brackish waters. Computer models of distribution, survival, reproduction and growth of the species predict that Dutch waters act as a source of comb jellies for other European waters. When coastal waters get warmer, spawning of the invasive species could increase and shift to earlier months. This can have consequences for food availability of other gelatinous species and fish such as anchovy, sprat and herring.

A pdf of the thesis can be downloaded here

Linked news

Friday 03 February 2017
Meer en eerder kwallen in de Noordzee
'De Amerikaanse ribkwal komt nu het meest voor en ook op hele andere plekken dan we voor mogelijk hielden'.

NIOZ publications

  • 2022
    Jak, R.G.; van Walraven, L.; van Oevelen, D. (2022). Voorstel voor monitoring van zoöplankton in de Noordzee. Monitoringplan zoöplankton MONS ID14. Wageningen Marine Research: Den Helder. 54 pp.
  • 2020
    Jager, Z.; van Walraven, L. (2020). Review of the possible interactions between Blue Energy and aquatic organisms. Deliverables 1.2 & 1.3 of project OOBE (Onderzoek Omgevingseffecten Blue Energy). NIOZ-rapport, 2020(04). NIOZ Royal Netherlands Institute for Sea Research: Texel. 56 pp.
    van Walraven, L.; Jager, Z. (2020). All Creatures Great and Small - Environmental Impact Study of Blue Energy, RED pilot Breezanddijk. Deliverables 2.4 & 2.5 of project OOBE (Onderzoek Omgevingseffecten Blue Energy). NIOZ-rapport, 2020(05). NIOZ Royal Netherlands Institute for Sea Research: Texel. 99 pp.
    van Walraven, L.; van Bleijswijk, J.; van der Veer, H.W. (2020). Here are the polyps: in situ observations of jellyfish polyps and podocysts on bivalve shells. PeerJ 8: e9260.
    Walles, B.; van Dalen, P.; van Walraven, L.; Grasman, S.; Wijsman, J.W.M. (2020). Shellfish as pre-filtration of marine intake water in a reverse electro dialysis energyplant: Effect of shellfish filtration during two experiments: Spring and Summer 2019 (Deliverables D3.2 and D3.3). Wageningen Marine Research: Yerseke. 31 pp.
  • 2018
    Jaspers, C.; Huwer, B.; Antajan, E.; Hosia, A.; Hinrichsen, H.-H.; Biastoch, A.; Angel, D.; Asmus, R.; Augustin, C.; Bagheri, S.; Beggs, S.E.; Balsby, T.J.S.; Boersma, M.; Bonnet, D.; Christensen, J.T.; Dänhardt, A.; Delpy, F.; Falkenhaug, T.; Finenko, G.; Fleming, N.E.C.; Fuentes, V.; Galil, B.; Gittenberger, A.; Griffin, D.C.; Haslob, H.; Javidpour, J.; Kamburska, L.; Kube, S.; Langenberg, V.T.; Lehtiniemi, M.; Lombard, F.; Malzahn, A.; Marambio, M.; Mihneva, V.; Møller, L.F.; Niermann, U.; Okyar, M.I.; Özdemir, Z.B.; Pitois, S.; Reusch, T.B.H.; Robbens, J.; Stefanova, K.; Thibault, D.; van der Veer, H.W.; Vansteenbrugge, L.; van Walraven, L.; Wozniczka, A. (2018). Ocean current connectivity propelling the secondary spread of a marine invasive comb jelly across western Eurasia. Glob. Ecol. Biogeogr. 27(7): 814-827.
    van Walraven, L.; Peperzak, L. (2018). Effect of a 100 Watt ultrasound transmitter on marine fouling. NIOZ-rapport, 2018(2). NIOZ: Texel. 97 pp.
  • 2017
    Tulp, I.; van der Veer, H.W.; Walker, P.; van Walraven, L.; Bolle, L.J. (2017). Can guild- or site-specific contrasts in trends or phenology explain the changed role of the Dutch Wadden Sea for fish? J. Sea Res. 127: 150-163.
    van Walraven, L.; Daan, R.; Langenberg, V.T.; van der Veer, H.W. (2017). Species composition and predation pressure of the gelatinous zooplankton community in the western Dutch Wadden Sea before and after the invasion of the ctenophore Mnemiopsis leidyi A. Agassiz, 1865. Aquat. Invasions 12(1): 5-21.
    van Walraven, L.; Dapper, R.; Nauw, J.J.; Tulp, I.; Witte, J.IJ.; van der Veer, H.W. (2017). Long-term patterns in fish phenology in the western Dutch Wadden Sea in relation to climate change. J. Sea Res. 127: 173-181.
  • 2016
    van Walraven, L. (2016). Flexible filter feeders : the gelatinous zoöplankton community in the Netherlands after the invasion of the ctenophore Mnemiopsis leidyi. PhD Thesis. [S.n.]: [s.l.]. ISBN 978-90-367-9294-3. 264 pp.
    van Walraven, L.; Driessen, F.; van Bleijswijk, J.; Bol, A.; Luttikhuizen, P.C.; Coolen, J.; Bos, O.G.; Gittenberger, A.; Schrieken, N.; Langenberg, V.T.; van der Veer, H.W. (2016). Where are the polyps? Molecular identification, distribution and population differentiation of Aurelia aurita jellyfish polyps in the southern North Sea area. Mar. Biol. (Berl.) 163: 172.
  • 2015
    van der Molen, J.; van Beek, J.; Augustine, S.; Vansteenbrugge, L.; van Walraven, L.; van Langenberg, V.; van der Veer, H.W.; Hostens, K.; Pitois, S.; Robbens, J. (2015). Modelling survival and connectivity of Mnemiopsis leidyi in the south-western North Sea and Scheldt estuaries. Ocean Sci. 11(3): 405-424.
    van Walraven, L.; Langenberg, V.T.; Dapper, R.; Witte, J.IJ.; Zuur, A.F.; van der Veer, H.W. (2015). Long-term patterns in 50 years of scyphomedusae catches in the western Dutch Wadden Sea in relation to climate change and eutrophication. J. Plankton Res. 37(1): 151-167.
  • 2014
    Augustine, S.; Jaspers, C.; Kooijman, S.A.L.M.; Carlotti, F.; Poggiale, J.-C.; Freitas, V.; van der Veer, H.W.; van Walraven, L. (2014). Mechanisms behind the metabolic flexibility of an invasive comb jelly. J. Sea Res. 94: 156-165.
    Cadée, G.C.; Dijksen, S.; van Walraven, L. (2014). Grote zeepaddenstoelen (Rhizostoma octopus) aangespoeld op Texel. Het Zeepaard 74(3): 98-105
  • 2013
    van Walraven, L.; Langenberg, V.T.; van der Veer, H.W. (2013). Seasonal occurrence of the invasive ctenophore Mnemiopsis leidyi in the western Dutch Wadden Sea. J. Sea Res. 82: 86-92.

Linked projects

Invasion of the ctenophore Mnemiopsis leidyi
Henk van der Veer
Project duration
15 Apr 2009 - 31 Dec 2015
REDstack_Environmental Effects of Blue Energy
Project duration
1 May 2016 - 30 Apr 2019