Seagrass ecosystem multifunctionality under the rise of a flagship marine megaherbivore
How does ecosystem functioning change now megaherbivores are returning? In our new paper today in Global Change Biology we show that the return of the green turtle has strong effects on seagrass ecosystem functions and can even reduce multifunctionality with ~25%. Read the short & simple summary below.
Green sea turtles are considered the megaherbivores of the coastal seas. Due to successful turtle conservation – many seagrass meadows across the globe have been transformed into their natural grazed state. Some are even becoming overgrazed show recent studies in India and Bermuda.
In an experiment along a grazing gradient from high to low turtle grazing, seven ecosystem functions where measured (e.g. coastal protection #carbon storage, nutrient cycling #biodiversity) simultaneously after 18mo. These were combined in 1 ecosystem-multifunctionality-index. Which is a new approach for marine habitats. This led to striking results.
Cages kept turtles from grazing the seagrass to mimic the –no-grazing scenario. Underwater field flumes, developed by the Royal Netherlands Institute of Sea Research, were used to measure sediment stability.
We found that medium turtle grazing pressure increased carbon storage and nutrient cycling of seagrass. While, fish biomass and other services were higher in meadows without turtle grazing. More importantly, we found simultaneous collapse of all services under severe grazing.
We argue that the return of the sea turtle should be accompanied with the protection of their habitat, seagrass meadows, as well as their predators, sharks, who can influence turtle grazing behaviour through fear effects. Watch this space for an upcoming paper by Fee Smulders et al.
By taking such integrative ecosystem approach to management we can maintain high ecosystem multifunctionality, as well as balanced ecosystems that can sustain natural densities of charismatic sea turtles.
Big thanks to Fee Smulders Arie Vonk Lisa Becking Tjeerd Bouma Rebecca James Jaco de Smit Jurjan van der Zee Per Palsboll Liesbeth Bakker et al. Wageningen Environmental Research NIOZ Royal Netherlands Institute for Sea Research Institute for Biodiversity and Ecosystem Dynamics – University of Amsterdam STINAPA Bonaire and our funders NWO Science