My work includes research on a wide range of topics in multiple aquatic ecosystems (seagrass beds, shellfish reefs, coral reefs, mangroves, fens). My interests include ecosystem functioning from a physiological to a landscape level and comprises both in-depth analysis and large-scale studies. For an overview of research projects see below.

Population connectivity and habitat use of mega-herbivores.

In this NWO funded research program we integrate data of sea turtles satellite tracking, stable isotope analysis, habitat mapping, animal physiology, and molecular tools to map sea turtle habitat use and population connectivity for the wider Caribbean to provide scientifically sound, ecosystem-based management strategies.

Back to the sea. Adult female green turtle on Zeelandia Beach St. Eustatius ready to rest after 1.5 hr of satellite tag processing.

Equipped with a satellite transmitter, an adult female green turtle is crawling back to sea in St. Eustatius.

 

Food web structure and restoration of foundation species (shell fish reefs), Wadden Sea

In this project we assessed the importance of habitat modification by reef builders (predominately mussels and oysters) for food web dynamics and biodiversity in the Wadden Sea. (Waddensleutels). Foundation species such as mussel beds and seagrass meadows have strongly declined due to human interference in the Wadden Sea. In this project I coordinated a unique, Wadden Sea wide food web study where we used stable isotope data of 10.000+ samples to develop new food web metrics to monitor nature conservation success. The project was a collaboration of three Dutch research institutes (RUG, NIOZ & NIOO) and two nature conservation organisations (Natuurmonumenten, Staatsbosbeheer) and developed innovative ways to restore the valuable intertidal mussel beds.

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Wadden Sea food web based on actual d15N and d13C stabile isotope values

 

Invasive seagrass, mega-herbivory and implications for seagrass ecosystem services (pilot)

At a regional scale (Caribbean) and in underwater exclosure experiments I monitor the spread of a recently introduced invasive seagrass species, the effect of stress (such as mega-herbivore grazing, and boat activity) on its spread, and how ecosystem services (fisheries production, nutrient cycling, carbon storage) of seagrasses are altered.

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Food choice experiments: Do green turtles like to eat invasive seagrass?

 

PHD

During my PhD project I studied the interactive effects of eutrophication, grazing and hydrodynamics on seagrass ecosystems. As a model system I studied tropical seagrass ecosystems, in Indonesia (Derawan Archipelago) that is also a global green turtle hotspot.

a) Eutrophication, Grazing & Resilience: Simultaneous effects of top-down control by megaherbivore grazing and bottom-up control by nutrient input (N&P) was experimentally tested in exclosure experiments. We found that intermediate levels of green turtle grazing increase the tolerance of seagrass ecosystems to eutrophication by the stimulation of seagrass production and concomitant nutrient uptake, the increased export of nutrients

Turtle exclosure

Cage experiment on the interactive effect of grazing & nutrient addition

b) Habitat collapse in Marine Protected Areas: We reported severe seagrass degradation in a decade-old MPA where hyper abundant green turtles adopted a previously undescribed belowground foraging strategy (digging for roots). These results reveal an unrecognized need to consider interactions of protected species with their habitat for sustainability. In this project, we used UAVs (drones) for counting turtles.

c) Coastal protection services: We found that short (grazed) seagrass meadows with most of their biomass in belowground tissues can also stabilize sediments and hence lower beach erosion rates. We used manipulative field experiments (under water bunkers and exclosures) and wave measurements.

Installing sandbags as wave-barriers

d) Toxicity: Seagrasses are declining at a global scale due to light reduction and toxicity events caused by eutrophication and increased sediment loading. In lab-experiments we found interactive effects of light reduction and toxicants (reduced nitrogen, NHx) on seagrass distribution and species succession  By understanding the drivers and interactions responsible for the functioning and degradation of seagrass systems we were also able to develop indicator tools and to provide insight for the management of seagrass ecosystems, and, at a larger scale, for marine protected areas (MPAs).

Laboratory experiment on ammonia toxicity in tropical seagrasses

Analyse the 1000’s of samples in Nijmegen

 

 

 

 

 

 

 

 

 

 

 

 

 

Multi-scale seagrass patterning in Shark Bay, Western Australia

The seagrass beds of Shark Bay, Western Australia, are among the most extensive and pristine in the world. In the shallows of the Faure Sill, seagrasses (Amphibolis antarctica) forms distinct multi-scale patterns which can be seen from the air. We are currently trying to find out what factors drive this unique self-organization of seagrasses.

Seagrass bands in Shark Bay

Dugongs in Shark Bay

Tjisse measuring plant fitness (PAM) at night in shark bay.

 

Other 

in-water surveys to gather (previously non-existing) baseline data green turtle populations in Indonesia

In the air: capturing green turtles rodeo-style

Population genetics of green turtle foraging aggregations

 

Impact on grazing on seagrass fauna (Derawan vs Spermonde archipelago, Indonesia)

 

Seagrass Patterns as indicators of seagrass resilience

UAV imagery showing seagrass patterns initiated by turtle grazing & hydrodynamics, Derawan

Aerial photography airplane launch (photo: Steve Oakley)

 

River nutrient and sediment load impact on coastal ecosystems.

Sampling seagrass to look at possible effects of sedimentation & eutrophication of the Berau river (blog)

 

Basic measurements on gap dynamics in transects

Happy hour @ seagrass meadow

 

Restoring fen water bodies; effects for aquatic macroinvertebrates

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Habitat connectivity of mangroves, coral reef, seagrass meadows for reef fish (Zanzibar, Pemba, Tanzania)

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One Response so far.

  1. Luis Rincon says:

    What an excellent experience!

    I work with seagrasses in Florida, micropropagation and see appkications of your work down the line!

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