University of Tasmania - Cape Bougainville

Restoration Project

University of Tasmania - Cape Bougainville

Restoration Objective:

The aim of this paper was to critically test the effect of H. erythrogramma on macroalgal habitat when the sea urchin occurs at relatively low but typically observable densities of 46 individuals per square meter.

Site Selection Criteria:

Experimental plots were established on sheltered reefs (2–10 m depth). Typical of sheltered coastal reefs in eastern Tasmania, these locations contained moderate densities of H. erythrogramma, and were associated with macroalgal impoverished rocky reef habitat, i.e. ostensibly sea urchin barrens habitat.

Cause Of Decline:

In temperate Australia, the sea urchin Heliocidaris erythrogramma is considered an ecologically important herbivore on shallow sub-tidal reef assemblages. However, there is a paucity of evidence demonstrating the capability of this species to graze and modify benthic habitats. Over much of its range H. erythrogramma is observed in association with macroalgal dominated rocky reefs where the sea urchin appears to have little or no influence on standing macroalgal communities. Nonetheless, in some parts of its range, and frequently observed on sheltered Tasmanian reefs, H. erythrogramma can be found in association with macroalgal impoverished rocky reefs ostensibly caused by the sea urchin consuming canopy-forming brown algae.

Key Reasons For Decline:

Overgrazing

Scientific Paper

Recovery of canopy-forming macroalgae following removal of the enigmatic grazing sea urchin Heliocidaris erythrogramma

S. D. Ling, S. Ibbott, J.C. Sanderson
Journal of Experimental Marine Biology and Ecology, Vol. 395.
https://doi.org/10.1016/j.jembe.2010.08.027

Organisation:

University of Tasmania

Site Observations:

Observation Date

1st Apr 1994 – 1st Jun 1996

Action Summary:

All visible H. erythrogramma (sea urchins), ranging ~60–100 mm test diameter, were hand collected from sheltered barrens in eastern Tasmania.

Lessons Learned:

H. erythrogramma, at sufficient densities, is capable of grazing and maintaining a sea urchin barrens state however this phenomenon is observed to manifest in sheltered waters only.

Project Outcomes:

In experimental plots where H. erythrogramma was removed, canopy-forming algae gradually recovered to demonstrate an average 5 times (ranging nil to 10 times) increase in percentage cover at 24 months post manipulation (chiefly driven by the habitat-formers Cystophora spp., Macrocystis pyrifera, Acrocarpia paniculata, and Sargassum spp.). While divergence in the overall algal community was indicated by both experiments, a statistically significant shift was only observed for one location at 24 months post urchin removal, suggesting that a complete canopy-driven shift in community structure will be gradual and will be contingent on urchin density remaining below approximately 1.5 m−2 in the longer term.

Key Reasons For Decline:

Overgrazing

Area of Restoration (Ha)

0

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Kelp Cover

26.5957
%
0.7979
%

Observation Date

31st Mar 1994 – 1st Jun 1996

Action Summary:

All visible H. erythrogramma (sea urchins), ranging ~60–100 mm test diameter, were hand collected from sheltered barrens in eastern Tasmania.

Lessons Learned:

H. erythrogramma, at sufficient densities, is capable of grazing and maintaining a sea urchin barrens state however this phenomenon is observed to manifest in sheltered waters only.

Project Outcomes:

In experimental plots where H. erythrogramma was removed, canopy-forming algae gradually recovered to demonstrate an average 5 times (ranging nil to 10 times) increase in percentage cover at 24 months post manipulation (chiefly driven by the habitat-formers Cystophora spp., Macrocystis pyrifera, Acrocarpia paniculata, and Sargassum spp.). While divergence in the overall algal community was indicated by both experiments, a statistically significant shift was only observed for one location at 24 months post urchin removal, suggesting that a complete canopy-driven shift in community structure will be gradual and will be contingent on urchin density remaining below approximately 1.5 m−2 in the longer term.

Key Reasons For Decline:

Overgrazing

Area of Restoration (Ha)

0

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Kelp Cover

85.2853
%
50.4505
%

Observation Date

30th Mar 1994 – 1st Jun 1996

Action Summary:

All visible H. erythrogramma (sea urchins), ranging ~60–100 mm test diameter, were hand collected from sheltered barrens in eastern Tasmania.

Lessons Learned:

H. erythrogramma, at sufficient densities, is capable of grazing and maintaining a sea urchin barrens state however this phenomenon is observed to manifest in sheltered waters only.

Project Outcomes:

In experimental plots where H. erythrogramma was removed, canopy-forming algae gradually recovered to demonstrate an average 5 times (ranging nil to 10 times) increase in percentage cover at 24 months post manipulation (chiefly driven by the habitat-formers Cystophora spp., Macrocystis pyrifera, Acrocarpia paniculata, and Sargassum spp.). While divergence in the overall algal community was indicated by both experiments, a statistically significant shift was only observed for one location at 24 months post urchin removal, suggesting that a complete canopy-driven shift in community structure will be gradual and will be contingent on urchin density remaining below approximately 1.5 m−2 in the longer term.

Key Reasons For Decline:

Overgrazing

Area of Restoration (Ha)

0

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Kelp Cover

7.6136
%
0.1136
%
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