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Habitat collapse due to overgrazing threatens turtle conservation in marine protected areas
Christianen, M.J.A.; Herman, P.M.J.; Bouma, T.J.; vn Katwijk, M.M.; Lamers, L.P.M.; van der Heide, T.; Mumby, P.J.; Silliman, B.R.; Engelhard, S.L.; van de Kerk, M.V.; Kiswara, W.; van de Koppel, J. (2014). Habitat collapse due to overgrazing threatens turtle conservation in marine protected areas. Proc. - Royal Soc., Biol. Sci. 281(1777): 20132890. dx.doi.org/10.1098/rspb.2013.2890
In: Proceedings of the Royal Society of London. Series B. The Royal Society: London. ISSN 0962-8452, more
Peer reviewed article  

Available in Authors 

Author keywords
    marine reserves; plant-herbivore interactions; alternate stable states

Authors  Top 
  • Christianen, M.J.A.
  • Herman, P.M.J., more
  • Bouma, T.J., more
  • vn Katwijk, M.M.
  • Lamers, L.P.M.
  • van der Heide, T.
  • Mumby, P.J.
  • Silliman, B.R.
  • Engelhard, S.L.
  • van de Kerk, M.V.
  • Kiswara, W.
  • van de Koppel, J., more

Abstract
    Marine protected areas (MPAs) are key tools for combatting the global over-exploitation of endangered species. The prevailing paradigm is that MPAs are beneficial in helping to restore ecosystems to more 'natural' conditions. However, MPAs may have unintended negative effects when increasing densities of protected species exert destructive effects on their habitat. Here, we report on severe seagrass degradation in a decade-old MPA where hyper-abundant green turtles adopted a previously undescribed below-ground foraging strategy. By digging for and consuming rhizomes and roots, turtles create abundant bare gaps, thereby enhancing erosion and reducing seagrass regrowth. A fully parametrized model reveals that the ecosystem is approaching a tipping point, where consumption overwhelms regrowth, which could potentially lead to complete collapse of the seagrass habitat. Seagrass recovery will not ensue unless turtle density is reduced to nearly zero, eliminating the MPA's value as a turtle reserve. Our results reveal an unrecognized, yet imminent threat to MPAs, as sea turtle densities are increasing at major nesting sites and the decline of seagrass habitat forces turtles to concentrate on the remaining meadows inside reserves. This emphasizes the need for policy and management approaches that consider the interactions of protected species with their habitat.

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