Data

Phase-shift dynamics of sea urchin overgrazing on nutrified reefs

University of Tasmania, Australia

Kriegisch, Nina ; Johnson, Craig, Prof. ; Ling, Scott, Dr

Viewed: [[ro.stat.viewed]] Cited: [[ro.stat.cited]] Accessed: [[ro.stat.accessed]]

ctx_ver=Z39.88-2004&rft_val_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Adc&rfr_id=info%3Asid%2FANDS&rft_id=https://metadata.imas.utas.edu.au/geonetwork/srv/eng/catalog.search#/metadata/21245d18-7a4f-4e25-9b98-ae90ae92748b&rft.title=Phase-shift dynamics of sea urchin overgrazing on nutrified reefs&rft.identifier=https://metadata.imas.utas.edu.au/geonetwork/srv/eng/catalog.search#/metadata/21245d18-7a4f-4e25-9b98-ae90ae92748b&rft.description=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.Maintenance and Update Frequency: notPlannedStatement: Small boulders and cobbles (0.20 - 0.50 m diam.) were sourced from the adjacent rocky reef and constructed into 28 patch reefs (each ~ 0.85 m2 planar area) on the sand patch. Reefs were separated by at least 5 m from each other and from the surrounding natural reef. The 28 boulder reefs were assigned randomly to a total of 4 treatments representing combinations of ‘reef ecosystem state’ (kelp beds vs urchin barrens) and ‘nutrient’ conditions (ambient vs enhanced), and within each treatment the 7 replicate reefs supported urchins at densities of 0, 4, 8, 12, 15, 20 and 24 urchins m-2. Three adult E. radiata individuals were transplanted to each appropriate patch reef to simulate the ‘kelp bed state’, providing a canopy cover of ~ 50% within the internal 0.25 m2 of each patch reef. 200 g of slow release fertiliser (Osmocote® Pro 3-4 M, 17N:4.8P:8.3K) was used to enhance nutrients on individual patch reefs. After randomly assigning the 4 different ‘reef state’ and ‘nutrient condition’ treatments to the experimental patch reefs, each of the 7 replicate patch-reefs within each treatment received (at random) one of 7 different urchin densities (0, 4, 8, 12, 15, 20 and 24 urchins m-2). Reefs were then checked every 3 weeks for the 12 months of the experiment to ensure urchin densities were maintained at their designated level. The amount of erect macroalgae on each reef was assessed every 3 months. Assessments were undertaken on SCUBA with in situ estimates of percentage cover of canopy-formers and understorey. Percentage cover assessments were performed using the point-intercept method (a 50 by 50 cm quadrat with 49 regularly spaced points defined by intersecting string lines, and an additional random point within the quadrat assigned in advance). Stipe counts were used to enumerate the abundance of canopy-forming brown algae (E. radiata, S. vestitum, and the introduced ephemeral Japanese kelp U. pinnatifida), and on the final assessment the total number of macroalgal species on each patch reef was counted.&rft.creator=Kriegisch, Nina &rft.creator=Johnson, Craig, Prof. &rft.creator=Ling, Scott, Dr &rft.date=2020&rft.coverage=westlimit=144.87; southlimit=-37.89; eastlimit=144.92; northlimit=-37.84&rft.coverage=westlimit=144.87; southlimit=-37.89; eastlimit=144.92; northlimit=-37.84&rft_rights=Creative Commons Attribution 4.0 International License http://creativecommons.org/licenses/by/4.0/&rft_rights=The citation in a list of references is: citation author name/s (year metadata published), metadata title. Citation author organisation/s. File identifier and Data accessed at (add http link).&rft_rights=The data described in this record are the intellectual property of the University of Tasmania through the Institute for Marine and Antarctic Studies.&rft_subject=biota&rft_subject=TEMPERATE ROCKY REEFS&rft_subject=PORT PHILLIP BAY, AUSTRALIA&rft_subject=REGIME-SHIFT&rft_subject=KELP BED COLLAPSE&rft_subject=KELP BED RECOVERY&rft_subject=ARTIFICIAL REEFS&rft_subject=MARINE ECOSYSTEMS&rft_subject=ROCKY COASTS&rft_subject=SEA URCHINS&rft_subject=NUTRIENTS&rft_subject=KELP FOREST&rft_subject=MACROALGAE (SEAWEEDS)&rft_subject=GRAZING DYNAMICS/PLANT HERBIVORY&rft_subject=HELIOCIDARIS ERYTHROGRAMMA&rft_subject=ECKLONIA RADIATA&rft_subject=Community Ecology&rft_subject=BIOLOGICAL SCIENCES&rft_subject=ECOLOGY&rft_subject=Ecosystem Function&rft_subject=ENVIRONMENTAL SCIENCES&rft_subject=ECOLOGICAL APPLICATIONS&rft_subject=Marine and Estuarine Ecology (incl. Marine Ichthyology)&rft_subject=Temperate Reef&rft_subject=research vessel&rft_subject=diver&rft_subject=Abundance of biota&rft_subject=Biotic taxonomic identification&rft.type=dataset&rft.language=English Access the data

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The citation in a list of references is: citation author name/s (year metadata published), metadata title. Citation author organisation/s. File identifier and Data accessed at (add http link).

The data described in this record are the intellectual property of the University of Tasmania through the Institute for Marine and Antarctic Studies.

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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.

Lineage

Maintenance and Update Frequency: notPlanned

Statement: Small boulders and cobbles (0.20 - 0.50 m diam.) were sourced from the adjacent rocky reef and constructed into 28 patch reefs (each ~ 0.85 m2 planar area) on the sand patch. Reefs were separated by at least 5 m from each other and from the surrounding natural reef. The 28 boulder reefs were assigned randomly to a total of 4 treatments representing combinations of ‘reef ecosystem state’ (kelp beds vs urchin barrens) and ‘nutrient’ conditions (ambient vs enhanced), and within each treatment the 7 replicate reefs supported urchins at densities of 0, 4, 8, 12, 15, 20 and 24 urchins m-2. Three adult E. radiata individuals were transplanted to each appropriate patch reef to simulate the ‘kelp bed state’, providing a canopy cover of ~ 50% within the internal 0.25 m2 of each patch reef. 200 g of slow release fertiliser (Osmocote® Pro 3-4 M, 17N:4.8P:8.3K) was used to enhance nutrients on individual patch reefs. After randomly assigning the 4 different ‘reef state’ and ‘nutrient condition’ treatments to the experimental patch reefs, each of the 7 replicate patch-reefs within each treatment received (at random) one of 7 different urchin densities (0, 4, 8, 12, 15, 20 and 24 urchins m-2). Reefs were then checked every 3 weeks for the 12 months of the experiment to ensure urchin densities were maintained at their designated level. The amount of erect macroalgae on each reef was assessed every 3 months. Assessments were undertaken on SCUBA with in situ estimates of percentage cover of canopy-formers and understorey. Percentage cover assessments were performed using the point-intercept method (a 50 by 50 cm quadrat with 49 regularly spaced points defined by intersecting string lines, and an additional random point within the quadrat assigned in advance). Stipe counts were used to enumerate the abundance of canopy-forming brown algae (E. radiata, S. vestitum, and the introduced ephemeral Japanese kelp U. pinnatifida), and on the final assessment the total number of macroalgal species on each patch reef was counted.

Notes

Purpose
To examine the dynamics of ecosystem phase shifts between productive kelp beds and impoverished sea urchin barrens.

Data time period: 2012-11-06 to 2013-12-02

This dataset is part of a larger collection

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text: westlimit=144.87; southlimit=-37.89; eastlimit=144.92; northlimit=-37.84

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Other Information

(DATA - community responses to sea urchin herbivory and nutrient enrichment (.xlsx) [direct download])

url : https://data.imas.utas.edu.au/attachments/21245d18-7a4f-4e25-9b98-ae90ae92748b/S1.xlsx External Link

MAP - General study area (imas:ARC_NKriegisch_Phaseshift_urchin_grazing_nutrified_reefs_MAP)

url : https://geoserver.imas.utas.edu.au/geoserver/wms External Link

(View and download this data through the interactive IMAS Data Portal.)

url : https://data.imas.utas.edu.au/portal/search?uuid=21245d18-7a4f-4e25-9b98-ae90ae92748b External Link

Identifiers

global : 21245d18-7a4f-4e25-9b98-ae90ae92748b