2 times cake: 2 cool new papers! How to keep seagrass as happy as a clam?

Today 2 papers of our group were published online! This papers are the result of a successful collaboration between the University of Groningen, NIOZ and Radboud University, The Netherlands

The first study by Els van der Zee et al. demonstrates that food web structure and complexity can be fundamentally shaped by habitat-modifying species.  This works through facilitation rather than trophic interactions , since habitat-modifying species  provide shelter and suitable attachment sites for other species. This was found after in-depth empirical investigations of two coastal ecosystems: North American temperate fringing marshes and West African tropical seagrass meadows (pdf: download from  www.penyu.nl/publication/ )   












In our second paper in Current Biology by Jim de Fouw et al. found  that – beyond coral bleaching – disruption of foundational marine mutualisms can cause rapid and large-scale ecosystem degradation: In a severe hot spell, breaking plant-mollusk partnerships speeds degradation. This we studied in the vast intertidal seagrass beds of Banc d’Arguin, Mauritania (West-Africa). Here the feedback loop between seagrass and lucinid bivalves with sulfide oxidizing gill bacteria drives landscape-scale degradation of tropical intertidal seagrass beds. Media coverage by ScienceNews on “How to keep seagrass ass happy as a clam” (pdf: download from  www.penyu.nl/publication/ )




Guest post: Jurjan’s research – turtle genomics

Within the Dutch Caribbean, green and hawksbill turtle rookeries and foraging grounds are found. Green and hawksbill turtles have been decimated by human exploitation and habitat degradation, calling for knowledge of population structure and demographic history. Here we investigate migration patterns in these highly migratory species and evaluate current population status. In other words: How many turtles were there and where to they go? Those are the central questions in my PhD which I will address using population genomics and ancient DNA.

Last summer I’ve spent three months in the Dutch Caribbean collecting tissue samples for my research. Most samples were collected on Bonaire, but a significant amount were collected on Curacao as well. A few samples were collected on Aruba as well. As soon as the samples arrive I will start on DNA extractions and analyses! Jurjan van der Zee20150910MC109214

Little-Curaçao-green-turtle swims 3100 km in 3 weeks

The track of green turtle female “MRC rentals” (after her sponsor) updated 10 october 2015. After nesting in Klein Curacao she swam 3100km in 30 days – and has now settled in Mexico, the foraging grounds in Chakmukchuuk or Laguna Manati.

Last week we* successfully placed a satellite transmitter on a big green turtle female after she nested at Little Curacao’s turtle beach. The signals of the ARGOS satellite are updated hourly and I am very happy to report that this female is swimming very fast in the direction of Nicaragua 1050km in the first 10 days. The first 2 days it first seemed she stayed around for another nest but then she decided to go for a long swim. UPDATE: this female has found her foraging ground and is now settled at Chakmukchuuk or Laguna Manati in Mexico after swimming 3100 km in 3 weeks.

Together with the other turtles that we deployed with transmitters we hope to learn more about population connectivity of sea turtles that nest and forage in the Kingdom of the Netherlands.

Below some more photo’s of green turtle named “MRC rentals” during the transmitter deployment process.

This lady was quite precise in choosing her nesting spot: She first took 5 hours to go on and off (4 times!) the beach to crawl around to check out nestings spots. Finally – around midnight – she chose part of the beach that was already cleared from plastic and washed up coral fans by Sea Turtle Conservation Curacao’s beach keepers and others. When she settled and starting to lay her eggs we put the wooden box around her and it took us 1.5 hours to fix the transmitter on her carapace with epoxy and putty. If she doesn’t rub her back too hard against coral boulders this transmitter could continue to send signals for the next year.

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Green turtle “MRC-rentals” finally found a place she liked after roaming the beach for 5 hours
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* The team on the beach: Sabine Berendse (Carmabi, Sea Turtle Conservation Curacao), me, Jurjan van der Zee (Groningen University), Funci (sea turtle conservation Bonaire) and not on this picture; Pieter de Geus (vet involved at STCC program), Andy (staff of Mermaid boat tours). Read this facebook post for more info on the very successful cooperation with Sea Turtle Conservation Curacao.
At 3:30 she was could finally go back to sea and rest
Spot-6 tag by Wildlife Computers
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The second logger on Klein Curacao in 2 nights!
In trance

Persbericht Carmabi 14 September 2015Omzwervingen Curaçaose zeeschildpadden vanaf nu per satelliet te volgen In de…

Posted by Sea Turtle Conservation Curacao on Monday, September 14, 2015

map_curacao tracking_Christianen_300s

Guest post: Fee’s research – turtle exclosures Lac Bay

I am Fee, the first master student who will monitor the exclusion cages in Lac Bay on Bonaire for three months. I arrived two weeks ago. My main research questions are:

  • How does turtle grazing affect the productivity of and competition between the native T. testudinum and invasive H. stipulacea in Lac Bay, and what are the differences in colonization rates between the species?
  • Does the green turtle show a preference for the native vs invasive seagrass species, and what are the differences in nutritional value?
  • How is the current seagrass distribution in Lac Bay compared to 2011 and 2013?

So I will try to assess the situation in the bay in order to hopefully eventually make a well-considered judgement call if we have to worry about the invasive species or if the ecosystem dynamics will adjust to this newcomer. In my first week, together with Marjolijn, we did a lot of fieldwork to train me for seagrass research.

The cages are situated in the middle of the bay, so with divetanks on kayaks we made adventurous trips towards our site. We took photos, measured the seagrass and took biomass samples, which Marjolijn later on taught me how to process and dry.

We also performed the first ‘cafetaria experiment’, in which we offer the sea turtles different choices of seagrass attached to metal pins in the seagrass bed, to see if they exhibit a preference. We already recorded one turtle grazing on the native turtle grass (as expected) and additionally encountered a turtle with a tag! This tag was put there by the Sea Turtle Conservation Bonaire, who immediately looked it up and found that the turtle had been tagged in 2011 and last seen in 2013. Now we know it is still healthy and roaming about Lac Bay.

Movie a day in the field with Fee (gopromovie by Lisette)




With some people of STCB and other students we went by boat to Klein Bonaire in the evening to await an adult turtle in order to put a transmitter on, but the turtle did not show up. We did however witness a hawksbill turtle nest hatching!


Bonaire is a beautiful island above and underwater. I am really surprised at how helpful and enthusiastic everybody is about marine research.  Updates will follow!


Satellite trackers show Bonaire green turtle habitat use

4 sub-adult green turtles that we caught in Lac Bay are now equipped with satellite transmitters to study their movements and use of the seagrass meadows, (see more photos below).

Mabel (STCB) and me deploying the satellite transmitter

The greens that forage in the shallow Lac Bay area are typically sub-adults. We selected some of the biggest turtles that forage here, to not only follow their foraging track in Lac Bay but also to have a chance of tracking them when they choose to migrate to their next foraging ground. It is assumed that as turtles grow bigger they need deeper waters for foraging, as bigger turtles have more buoyancy and thus difficulties to stay on the bottom in shallow areas. For the last 3 weeks the turtles tags are transmitting their GPS location via the Argos satellite and below you find a map of the first rough results of 1 of the turtles. This turtle is commuting between a patch of seagrass in the bay where it forages in the daytime and the deeper reef for resting during the night. At some nights the turtle was also spotted in the bay and it might sleep there too.

GPS locations of a sub-adult green turtle in Lac Bay Bonaire. The turtle grazes in the bay, and sleeps predominantly on the reef.
GPS locations of a sub-adult green turtle in Lac Bay Bonaire. The turtle grazes in the bay, and sleeps predominantly on the reef.


Are you diving in Bonaire and have you seen green turtles with satellite transmitters? Report your observations by sending me an email or respond to this post! Just describe, where and when you have seen the turtle. Which turtle did you see? You might have notice a mark? Every turtle has an individual colored mark next to the transmitter. Marks are: a blue “A”, pink square, yellow triangle, white cross, red circle.

We are also interested in: the turtle’s behavior, at which depth? Were the satellite tag and antenna still OK (see below) – turtles loves to scratch their backs to the coral. And .. please don’t touch the turtle. Your help is much appreciated! Thank you!

Movie: Time lapse series of First logger placed on subadult turtle by STCB & RUG at Lac Bay Bonaire

Also Read STCB blogpost:The Beginning of a Great Partnership Two weeks ago Marjolijn Christianen and her team (Jurjan van der Zee and Sandra…Posted by Sea Turtle

Working on transmitter deployment during STCB's 4-yearly monitoring surveys in Lac Bay.
Working on transmitter deployment during STCB’s 4-yearly monitoring surveys in Lac Bay.
Releasing the turtle in Lac Bay, she disappeared as lightning
Releasing the turtle in Lac Bay, she disappeared as fast as lightning
The transmitter, a SLASH10 from Wildlife computers
The transmitter, a SLASH10 from Wildlife computers
This turtle has just been capured by Funchi while it was resting on the reef at 10 m deep. Waiting for the boat in rough seas.
This turtle has just been capured by Funchi while it was resting on the reef at 10 m deep. Waiting for the boat in rough seas.

Experiment on (invasive) seagrass & turtle grazing, Bonaire

Two weeks ago we arrived on Bonaire. Since then we worked non-stop and we made great progress! The first thing we did was to set up a turtle exclosure experiment on the seagrass beds in Lac Bay, after Funchi (STCB) and Sabine Engel (STINAPA) kindly showed us all the suitable seagrass areas. The native dominant seagrass species here are Thalassia testudinum (or turtle grass) and Syringodium filiforme. However after a quick snorkel survey across the bay the cover of invasive seagrass species Halophila stipulacea seems almost higher.

That is impressive since the species was reported only in 2010 for the first time in Lac Bay. NGO Sea Turtle Conservation Bonaire that works since 1991 on turtles here estimates the sea turtle population (green and hawksbill) between 1000-2000 turtles – predominantly sub-adult green turtles that graze on seagrass in the shallow bay. We know that turtles are reported eating on the invasive seagrass but there are still a lot of unknowns:

  • What the effect of turtle grazing on seagrass production, species composition, nutrient availability, invasive seagrass expansion rate
  • Does H. stipulacea have the same nutritional value?
  • What happens with the carrying capacity of Lac’s seagrass meadow if the native seagrass species is being replaced by the invasive species?

The underwater cages that we use to prevent turtles from grazing certain seagrass patches will be followed during the next years by MSc students in cooperation with Imares, STCB and STINAPA.

Have a look at these first pictures below. And this Facebook post: https://www.facebook.com/karko.bonaire?pnref=story

Marjolijn building underwater cage in turbid waters
Marjolijn building underwater cage in turbid waters
Invasive Halophila stipulacea between Thalassia
Invasive Halophila stipulacea between Thalassia
Sharp borders between unglazed and grazed Thalassia testudinum patches. Likely used in a rotational grazing scheme by Green turtles
Sharp borders between unglazed and grazed Thalassia testudinum patches. Likely used in a rotational grazing scheme by Green turtles
Funchi (STCB) and Sabine (STINAPA) point out grazed Thalassia seagrass beds of Lac Bay, Bonaire
Funchi (STCB) and Sabine (STINAPA) point out grazed Thalassia seagrass beds of Lac Bay, Bonaire
Grazed Thalassia testudinum in and outside cages at the start of our experiment
Grazed Thalassia testudinum in and outside cages at the start of our experiment
Halophila stipulacea in Lac Bay. Dominant in large parts of the Bay
Halophila stipulacea in Lac Bay. Dominant in large parts of the Bay


Sea turtle fieldwork in Dutch Caribbean 2015

I am very excited to finally start our fieldwork on sea turtles and seagrass in the Bonaire, Aruba and Curacao! What started as a proposal (initiated by Lisa Becking and me) in August 2013, finally resulted in a research project May 2015 entitled  “Ecology and conservation of Green and Hawksbill turtles in the Dutch Caribbean”. Jurjan van der Zee (the PhD student in the project) will focus on sea turtle population dynamics. During his first fieldwork ever he will collect loads of DNA samples of hatchling and (sub-)adult turtles. My part of the research focuses on sea turtle migration (using satellite tracking, isotope studies), and sea turtle habitat use (turtle exclosure studies on seagrass meadows, GIS habitat mapping). Sandra Striegel is joining us for her MSc. project on temperature effects on sea turtle hatchling sex ratios. Now hopefully the satellite trackers arrive next week in Bonaire, and our extensive planning together with our counterparts – Sea turtle conservation Bonaire, TurtugAruba, and Carmabi – will result in a successful fieldwork campaign! Thanks also to Per Palbøll (PI of the project) and our funding agency NWO. I will be back in 2 months and hopefully posts some updates about the fieldwork here!

Map Bonaire in Caribbean

12.000 stable isotope samples of the Wadden Sea

Who eats who in the Wadden Sea? We collected 12000 samples in one of the largest dbases of stable isotope samples. Using these samples we found that the energy in the Wadden Sea (primary production) is mainly provided by the production of benthic algae (diatoms) on the tidal flats. Papers about this are underway but the first results can be found in our scientific report & glossy


Now online: “Wadden Natuur Kaart”

The Wadden Natuur kaart (Wadden Sea Nature Map) is now online: this is one of the publications of the Waddensleutels project on which I worked in the last 2+years. You should definitively explore and test it. For example; activate the benthos hotspot layer (upper left) and see which areas are most interesting as foraging areas for birds. Or check out where intertidal musselbeds occured for 5 years or more (in last 17 years). Or combine a map of shrimp fishery intensity and biodiversity. Our newly developed habitat map allows you to do these analysis per habitat type. Have a go at it. Use this interactive map to make your own map using just your web browser, print it or download it  or continue in a GIS program. In the photo you see Han Olff & Sander Holthuijsen exploring the map at a large touch screen during the symposium in Leeuwarden.

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More Waddensleutels publications here

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