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
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:
After months of radio/blog silence (I did not want to bore you with another photo of my computer screen) I finished the manuscript of my PhD thesis just before the deadline of 1th of October, Woehoe! The last weeks I lived a life comparable to a burrowing shrimp: I lived inside my office, only shoveling the manuscripts over to all my supervisors on a regular basis.
I will defend my PhD-thesis titled “Seagrass systems under nutrient loads, hydrodynamics and green turtle grazing – Do green turtles rule the seagrass world?” at the Radboud Universiteit Nijmegen on March 22nd 2013 at 13:00. Now it is time to go on seagrass expedition to Bank D’Arguin, Mauretania.
Underwater meadow. Seagrass beds, like this one teeming with silverside fish off of Indonesia’s Bone Batang Island, are key habitats for young fish as well as the occasional larger mammal.Credit: Marjolijn J.A. Christianen
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!
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.
To get an idea of green turtle densities on foraging grounds around the Derawan Archipelago I hopped over the border to Malaysia to visit the islands around Semporna (Mabul, Sipadan, Pom Pom, & Pandanan). Steve Oakley and Celebes Beach resort were so kind to host me on Pom Pom Island. Read the blog post by Steve Oakley on our work here, also if you are looking for a student project on turtles. High densities on the seagrass here! But Derawan turtle densities are still on top. Turtles here are more restricted to a limited time frame for grazing due to a different tide. On Sipadan I found a lot of juvenile turtles that grazed on hairlike Halodule uninervis in only 15cm of water. On the coral reef turtles could be approached so close that I could read the tag numbers and most of the subadult turtles had flippertags all tagged on Sipadan itself. The turtles seem to stay for a long time on the same place. The Green turtles are real fish-spa addicts, so many times you see the green turtle stretching out in a cloud of cleaner wrass and cleaner emperor fish, and on Sipadan I saw a group of 8 turtles fighting (biting!) over taking over the best spa-spot on a big rock.
The last fieldwork of my Phd is finished! While writing this blog post in Dubai on the way back to the Netherlands the dried seagrass samples patiently wait on the seat next of me, together with the other 70kg of equipment where I travel with. The first unofficial results are promising. On the aerial pictures we clearly see different patterns of gaps on the 3 different stations that lie on increasing distance from the beach.
The grazing effect on the seagrass is enormous, which is clear if you remove the cages that kept away the grazing turtles. Seagrass regrows quicker into gaps behind wave barriers. And the effect of waves and grazing seem to differ between the stations, so now it is time to spend some hours analyzing the huge amount of data that we have collected and write the results up.
In these last months we had quite a lot visitors. Research (photo) journalist Hans Wolkers visited a few weeks to write an article about our research here. With his too infected he could not photograph the turtles during his last days so he ended up helping to sort out numerous seagrass samples 🙂 . And we also had family/boy/girlfriends of Iris and Peter and my sister around. it was a lot of fun having him here. Hans, Sara, Sabine, Jelco, Ger thanx a lot for the help!