Symposium: Wadden Sea foodweb & role of ecosystem engineers

The Waddensleutels project finished 16 april 2015 with a symposium in Leeuwarden, and with that also my 1st post-doc project.  Topics here were: Which measures should we take to increase the area of musselbeds in the Dutch Wadden Sea & what is the current foodweb stucture and state (and how is this affected by the presence of mussel beds)? We learned that mussel beds are of vital importance for the Wadden sea. Musselbeds increased the biomass of benthos, fish and birds upto 4 times compared to bare surrounding areas. Mussel beds really are the foundations of life in the Wadden Sea.

These results can be found in our scientific report & glossy

Schermafbeelding 2015-04-17 om 22.13.55


Fieldwork Derawan 2014 photo series

I had the opportunity to go back to Derawan for 3 more weeks of fieldwork, thanks to the Schure Beijerink Popping foundation. I gathered samples for food web analysis, checked the current turtle density and seagrass biomass, recaptured green turtles and made a new series of aerial photographs with a kite (with super assistant Sipke in the 1st week). I also searched from pygmy seahorses, frogfishes and lembeh sea dragons and found them all. Enjoy the photo’s and leave a comment!


Green turtles threaten their own food source in MPAs: New paper Proceedings B

Our new paper is out in Proceedings of the Royal Society B! Green turtle populations have expanded so much in Indonesia’s east coast islands marine protected areas that they are adopting new feeding habits, degrading the ecosystem and threatening their own conservation. Read more about  “Habitat collapse due to overgrazing threatens turtle conservation in marine protected areas” and download the paper here.

After press coverage of the Associated Press the news has gone viral! see Washington Post, Time and others


Food Web collection Waddensleutels 2013

This summer we (the Waddensleutels team) visited all dutch Wadden Islands to collect samples for food web comparisons between mussel beds and surrounding habitats. It was a very successful operation. We collected around 1800 samples of organism that are now going to be analyzed for stable isotopes at the NIOZ, Texel. Sampling involved fishing with fykes (also during nighttime), benthos cores, algal sampling, but also measuring the height profile of the mussel bed, the hydrodynamics, mussel production and much more. We are very grateful for the help of the many volunteers that helped us!  The pictures will tell you much more about the research & show some of our surprising catches, check it out:


Many thanks to Arjen de Ruiter en Peter Visser for providing some of the Pictures!

Also see this newsletter ( in dutch; nieuwsbrief Waddensleutels november 2013)

PhD thesis online

You can download my PhD thesis “Seagrass systems under nutrient loads, hydrodynamics and green turtle grazing – Do turtles rule the seagrass world?” here (pdf 88 MB). And the papers of my thesis here.
Next friday I will defend my PhD thesis at Radboud University Nijmegen.
I still have some paper copies left. So send me an email if you want me to send it to you. If you want to watch the live videostream of my defence mail me for the link.
Please don’t hesitate to contact me if you have any comments after reading my thesis. Look forward to it!

10th ISBW Buzios, Brasil (& sea hares)

The 10th international seagrass biology workshop was a success! Together with seagrass specialists from around the globe we enjoyed 3 days packed with talks & workshops in a resort town of Buzios in Brasil. See WSA’s blog by Sity for a nice overview of the highlights and of the speakers (gallery seagrass watch)

It also included a field trip to the seagrass (Halodole wrightii) meadows of  Ilha do Japonês, Cabo Frio. Here Dominik and I found some small green turtles above the seagrass bed and loads of sea hares swimming and mating.

Together with the other young seagrass punks we had a great conference! See then here in their natural habitat:

Many thanks to Tjeerd & Leon to provide funding for this great opportunity

Seagrass expedition Bank d’Arguin, Mauretania

The Bank d’Arguin is a magnificent place: Not only to see loads of beautiful birds, some marked with colourfull rings as a souvenir from the Netherlands, but also to do seagrass research. Together with Jim de Fouw (our expedition leader), Laura Govers, Tjisse van der Heide en Karin van de Reijden we traveled through the Mauritanian desert to the Bank d’Arguin research station.

This station has been used for decades by many researchers, which can be noticed by the strange collections of research equipement: fake birds, umbrella’s, cages, nets, loads of rain meters (desert??) and snow rackets. These snow rackets were used the next day (don’t worry: no climate change-induced snow storm in the desert) to walk on the mudflats to reach our seagrass plots, to prevent to sink knee deep in the mud, which did occur to Laura due to a broken racket. The tidal flats are dominated by seagrass: in the intertidal Zostera noltii and a bit of Halodule whrightii and subtidal Cymodocea nodosa. Contrasting to the tropical reeftop seagrass meadows where I usually work, here, the seagrasses build up a hudge amount of organic matter and trap a lot of suspended particles so that the mudflat is raised by a couple of centimeters per year. In an experiment we test the effect of this phenomena and bivalves on seagrasses. Another series of experiment and observations focussed on the seagrass foodweb. Unfortunately snorkeling is not really a lot of fun here because of the poor visibility. Above the seagrass we encountered a lot of bottlenose dolphins (twice the size of the Indo-Pacific ones), fidler crabs, shoavelnose-, torpedo-, and sting-rays, jumping yellow mullets, borrowing crabs, Cymbium shells, and in the ground under the seagrass off course loads of the world-famous Loripes lacteus and Anadara (“Shell”-) shells.

A very dramatic sight was the enormous amount of dead green turtle carapaces that were washed up the beach and eaten by jackals in the previous month; approximately 1 dead turtle every 20 meter at a stretch of 3km beach. There was no sign of poaching (cuts in the carpace) or hunger, the carapace lenght (CCL) ranged from 40 cm till 90 cm, and the local rangers and researchers also don’t have a clue what happened here, leave a comment if you know more! Some random photos: