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Phase-shift dynamics of sea urchin overgrazing on nutrified reefs

Citation

Kriegisch, N and Reeves, S and Johnson, CR and Ling, SD, Phase-shift dynamics of sea urchin overgrazing on nutrified reefs, PLoS One, 11, (12) Article e0168333. ISSN 1932-6203 (2016) [Refereed Article]


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Copyright Statement

© 2016 Kriegisch et al. icensed under Creative Commons Attribution 4.0 International (CC BY 4.0) https://creativecommons.org/licenses/by/4.0/

DOI: doi:10.1371/journal.pone.0168333

Abstract

Shifts from productive kelp beds to impoverished sea urchin barrens occur globally and represent a wholesale change to the ecology of sub-tidal temperate reefs. Although the theory of shifts between alternative stable states is well advanced, there are few field studies detailing the dynamics of these kinds of transitions. In this study, sea urchin herbivory (a ‘top-down’ driver of ecosystems) was manipulated over 12 months to estimate (1) the sea urchin density at which kelp beds collapse to sea urchin barrens, and (2) the minimum sea urchin density required to maintain urchin barrens on experimental reefs in the urbanised Port Phillip Bay, Australia. In parallel, the role of one of the ‘bottom-up’ drivers of ecosystem structure was examined by (3) manipulating local nutrient levels and thus attempting to alter primary production on the experimental reefs. It was found that densities of 8 or more urchins m-2 (≥ 427 g m-2 biomass) lead to complete overgrazing of kelp beds while kelp bed recovery occurred when densities were reduced to ≤ 4 urchins m-2 (≤ 213 g m-2 biomass). This experiment provided further insight into the dynamics of transition between urchin barrens and kelp beds by exploring possible tipping-points which in this system can be found between 4 and 8 urchins m-2 (213 and 427 g m-2 respectively). Local enhancement of nutrient loading did not change the urchin density required for overgrazing or kelp bed recovery, as algal growth was not affected by nutrient enhancement.

Item Details

Item Type:Refereed Article
Keywords:regime shift, ecosystem collapse, recovery, conservation
Research Division:Biological Sciences
Research Group:Ecology
Research Field:Marine and Estuarine Ecology (incl. Marine Ichthyology)
Objective Division:Environment
Objective Group:Control of Pests, Diseases and Exotic Species
Objective Field:Control of Animal Pests, Diseases and Exotic Species in Coastal and Estuarine Environments
Author:Kriegisch, N (Ms Nina Kriegisch)
Author:Reeves, S (Mr Simon Reeves)
Author:Johnson, CR (Professor Craig Johnson)
Author:Ling, SD (Dr Scott Ling)
ID Code:113555
Year Published:2016
Deposited By:Centre for Ecology and Biodiversity
Deposited On:2017-01-06
Last Modified:2017-03-22
Downloads:16 View Download Statistics

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