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Marine reserves reduce risk of climate-driven phase shift by reinstating size- and habitat-specific trophic interactions


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Ling, SD and Johnson, CR 2012 , 'Marine reserves reduce risk of climate-driven phase shift by reinstating size- and habitat-specific trophic interactions' , Ecological Applications, vol. 22, no. 4 , pp. 1232-1245 .

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Spatial closures in the marine environment are widely accepted as effective
conservation and fisheries management tools. Given increasing human-derived stressors acting
on marine ecosystems, the need for such effective action is urgently clear. Here we explore
mechanisms underlying the utility of marine reserves to reinstate trophic dynamics and to
increase resilience of kelp beds against climate-driven phase shift to sea urchin barrens on the
rapidly warming Tasmanian east coast. Tethering and tagging experiments were used to
examine size- and shelter-specific survival of the range-extending sea urchin Centrostephanus
rodgersii (Diadematidae) translocated to reefs inside and outside no-take Tasmanian marine
reserves. Results show that survival rates of C. rodgersii exposed on flat reef substratum by
tethering were approximately seven times (small urchins 10.1 times; large urchins 6.1 times)
lower on protected reef within marine reserve boundaries (high abundance of large predatorycapable
lobsters) compared to fished reef (large predatory lobsters absent). When able to seek
crevice shelter, tag-resighting models estimated that mortality rates of C. rodgersii were lower
overall but remained 3.3 times (small urchins 2.1 times; large urchins 6.4 times) higher in the
presence of large lobsters inside marine reserves, with higher survival of small urchins owing to
greater access to crevices relative to large urchins. Indeed, shelter was 6.3 times and 3.1 times
more important to survival of small and large urchins, respectively, on reserved relative to
fished reef. Experimental results corroborate with surveys throughout the range extension
region, showing greater occurrence of overgrazing on high-relief rocky habitats where shelter
for C. rodgersii is readily available. This shows that ecosystem impacts mediated by range
extension of such habitat-modifying organisms will be heterogeneous in space, and that
marine systems with a more natural complement of large and thus functional predators, as
achievable within no-take reserves, will minimize local risk of phase shifts by reinstating size
and habitat-specific predator–prey dynamics eroded by fishing. Importantly, our findings also
highlight the crucial need to account for the influence of size dynamics and habitat complexity
on rates of key predator–prey interactions when managing expectations of ecosystem-level
responses within marine reserve boundaries.

Item Type: Article
Authors/Creators:Ling, SD and Johnson, CR
Keywords: Centrostephanus rodgersii; climate change; fishing; kelp beds; marine protected areas; predation; range extension; resilience; sea urchin; spatial refuge; Tasmanian temperate reefs; urchin barrens.
Journal or Publication Title: Ecological Applications
Additional Information:

Copyright 2012 Ecological Society of America

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