Restoration Project

University of Tasmania - Bicheno

Restoration Objective:

The aim of this study was to examine the impact of the range-extending sea urchin Centrostephanus rodgersii on reef habitat structure and associated biodiversity within their extended range in Tasmania by using controlled sea urchin removals.

Site Selection Criteria:

This study targeted sites that once had kelp but had been converted to urchin barrens.

Cause Of Decline:

Driven by increased poleward penetration of the warm East Australian Current (EAC), the sea urchin Centrostephanus rodgersii (Diadematidae) has recently undergone a southern range extension in temperate south-eastern Australia. These urchins are able to eliminate macroalgal habitat and effect a catastrophic shift to an alternative sea urchin ‘barrens’ state. Thus, C. rodgersii grazing in eastern Tasmania is considered to pose a major threat to the structure and functioning of the biologically diverse macroalgal-dominated rocky reefs.

Key Reasons For Decline:

Overgrazing

Scientific Paper

Range expansion of a habitat-modifying species leads to loss of taxonomic diversity: a new and impoverished reef state

S.D. Ling, , Oecologia, Vol. 156.https://doi.org/10.1007/s00442-008-1043-9

Organisation:

University of Tasmania

Site Observations:

Observation Date

19th Nov 2003 – 9th Nov 2005

Action Summary:

The long-spined sea urchin (Centrostephanus rodgersii) was removed from incipient barrens patches at an eastern Tasmanian site, and the macroalgal response and invertebrate diversity was monitored relative to unmanipulated barrens patches.

Project Outcomes:

In all incipient barrens patches from which C. rodgersii was removed, a structurally complex assemblage of foliose algae developed that was ultimately dominated by Ecklonia radiata and Phyllospora comosa. Filamentous algae and macroalgal sporophytes (height20 mm) recruited to available space and began to overgrow the substratum within 1 month. The pattern of re-colonisation for E. radiata (by cover) occurred consistently across C. rodgersii removal patches, while significant between-patch variability was detected for P. comosa and total canopy cover.

Key Reasons For Decline:

Overgrazing

Area of Restoration (In Square Metres)

7.1

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Kelp Cover

21.32132132
%
0
%
Costings:
Cost Currency:USD

Observation Date

19th Nov 2003 – 9th Nov 2005

Action Summary:

The long-spined sea urchin (Centrostephanus rodgersii) was removed from incipient barrens patches at an eastern Tasmanian site, and the macroalgal response and invertebrate diversity was monitored relative to unmanipulated barrens patches.

Lessons Learned:

Removal of urchins can result in a macroalgal community that converges with natural kelp forests in diversity. Grazing activity of C. rodgersii results in an estimated minimum net loss of approximately 150 taxa (invertebrates and algae) typically associated with Tasmanian macroalgal beds in this region. Vertebrate diversity was not compared between groups.

Project Outcomes:

In barrens patches from which C. rodgersii was removed, there was a rapid proliferation of canopy-forming macroalgae (Ecklonia radiata and Phyllospora comosa), and within 24 months the algal community structure had converged with that of adjacent macroalgal beds where C. rodgersii grazing was absent. In the recovered macroalgal habitat, faunal composition redeveloped similar to that from adjacent intact macroalgal beds. In contrast, the faunal community of the barrens habitat is overwhelmingly impoverished. Grazing activity of C. rodgersii results in an estimated minimum net loss of approximately 150 taxa typically associated with Tasmanian macroalgal beds in this region.

Key Reasons For Decline:

Overgrazing

Area of Restoration (In Square Metres)

7.1

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Kelp Cover

48.75776398
%
0
%
Costings:
Cost Currency:USD