MEPS 384:83-96 (2009)  -  doi:10.3354/meps08024

How effective are MPAs? Predation control and ‘spill-in effects’ in seagrass–coral reef lagoons under contrasting fishery management

Johan S. Eklöf1,4,*, Sara Fröcklin1, Annika Lindvall1, Nadja Stadlinger1, Alex Kimathi2, Jacqueline N. Uku2, Tim R. McClanahan3

1Department of Systems Ecology, Stockholm University, 106 91 Stockholm, Sweden
2Kenyan Marine and Fisheries Research Institute, PO Box 81651, 080100 Mombasa, Kenya
3Marine Programs, Wildlife Conservation Society, Bronx, New York 10460-1099, USA
4Present address: Department of Marine Benthic Ecology and Evolution, Biological Centre, University of Groningen, Kerklaan 30, PO Box 14, 9750 AA Haren, The Netherlands

ABSTRACT: Marine protected areas (MPAs) are heavily promoted as a panacea for marine conservation, but lagging and sometimes idiosyncratic protection effects bring their overall effectiveness into question. In Kenyan lagoons, seagrass overgrazing by the sea urchin Tripneustes gratilla has been linked to removal of predators, but overgrazing has also been observed within well-protected MPAs. In this study we investigated the effectiveness of Kenyan MPAs in facilitating predation control over sea urchins, particularly T. gratilla, in relation to system (seagrass or coral reef), distance to reefs, and seagrass presence. A strong protection effect on urchin densities on reefs and a negative correlation between T. gratilla density and predation pressure (from sea stars, fish and gastropods) in seagrass beds (r2 = 0.345) confirmed the importance of top-down control. Yet there were no clear effects of protection or distance to reefs in seagrass beds, most likely due to (1) low predator densities in the recently established Mombasa MPA; (2) ‘spill-in’ of aggregated T. gratilla into the older Watamu MPA (potentially facilitated by low predation pressure on the large urchins and nutrient enrichment); and (3) a potential buffering effect of seagrass canopies on predation, regardless of distance to reefs. Effects of seagrass presence differed between areas, but indicated that overgrazing in some areas could be self-regulated by inducing higher urchin mortality. As MPA effects appear to be system-, time- and site-specific, managers should also assess other more holistic approaches (e.g. banned fishing of urchin predators and reduced nutrient input from land runoff) to protect seagrasses.

KEY WORDS: Marine protected areas · Indirect effects · Trophic cascades · Seagrass · Tripneustes gratilla · Thalassodendron ciliatum · Kenya · Shelter

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Cite this article as: Eklöf JS, Fröcklin S, Lindvall A, Stadlinger N, Kimathi A, Uku JN, McClanahan TR (2009) How effective are MPAs? Predation control and ‘spill-in effects’ in seagrass–coral reef lagoons under contrasting fishery management. Mar Ecol Prog Ser 384:83-96

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