How do green sea turtles influence sediment carbon dynamics in tropical #seagrass ecosystems? This is exactly what Susi Rahmawati is investigating during her PhD in our group at WUR….
(more…)Category: Fieldwork
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Satellite tags placed on nesting green turtles, St. Eustatius
Based on the monitoring data on nesting turtles that Jessica Berkel and her team at STENAPA are collecting we were able to predict the turtle’s return to the beaches. For this we used the inter-nesting durations of the first green turtles tracks that were reported for Zeelandia beach, St. Eustatius. Equipped with a turtle box, satellite transmitters, our red headlights and the turtle research kit we headed to the beach and already after an hour of beach patrols we found a female green turtle. (more…)
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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 (more…)
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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.
More Waddensleutels publications here
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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!
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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)
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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:
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Time Lapse Derawan
After all those weeks behind the computer I am already longing back to my view from my research base in Derawan, enjoy my time lapse video. Do you see the tide rising?
2 last hours of sun on a typical fieldwork day.
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Green turtle stuff around Derawan
In total now we captured and measured more than 800 green turtles around Derawan and tagged 500 of them. The WWF guys (Udin, Darjon), some locals (Jeffrey, Tiar) and we catched them using the rodeo technique. This year we recaptured some individuals that we tagged previously in 2009 on Derawan Island. These turtles grew 3-6 cm (curved carapace lenght) or 3-10 kgs. On her first day on Derawan my sister Sabine saw green turtles in all kind of sizes and activities; she saw an female laying eggs, and small hatchlings coming out of their nest and she was my research assistant while cathcing green turtles in the seagrass meadow. Again a lot of pictures, enjoy because this will be the last pictures from the field for a while!
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Seagrass Fauna part 2
One of the cool things of seagrass meadows is that at first sight it might not seem too rich in animal life. But when working for hours on the seagrass around our cages and sandbags you find cool new animals that you might miss normally. In the last weeks I went out to make the perfect green-turtle-grazes-on-seagrass-picture but every time the visibility was crap or it was too deep or the current was too strong but then during the struggle under water I found 2 of my favourite animals (just in front of my house !): the robust ghostpipefish and a orange frogfish (species still needs identification).
BTW: I can recommend the sandbags to anyone interested in studying the settlement of flora/fauna.
