From Australian Oceans Data Network
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Phase-shift dynamics of sea urchin overgrazing on nutrified reefs

Created 23/06/2025

Updated 23/06/2025

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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.

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Additional Info

Field Value
Title Phase-shift dynamics of sea urchin overgrazing on nutrified reefs
Language eng
Licence Not Specified
Landing Page https://data.gov.au/data/dataset/dd7597e8-367c-4fa3-813f-fb13e2bb37b4
Contact Point
Australian Ocean Data Network
nkriegisch@gmx.de
Reference Period 06/11/2012 - 02/12/2013
Geospatial Coverage
Map data © OpenStreetMap contributors
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      ],
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Data Portal Australian Oceans Data Network

Data Source

This dataset was originally found on Australian Oceans Data Network "Phase-shift dynamics of sea urchin overgrazing on nutrified reefs". Please visit the source to access the original metadata of the dataset:
https://catalogue.aodn.org.au/geonetwork/srv/eng/csw/dataset/phase-shift-dynamics-of-sea-urchin-overgrazing-on-nutrified-reefs