University of Tasmania - Bruny Island

Restoration Project

University of Tasmania - Bruny Island

Restoration Objective:

This study aimed to identify factors responsible for the persistence of barrens created by H. erythrogramma in Tasmania, by assessing whether recovery of native canopy-forming algae on sea urchin barrens can be inhibited in the absence of intense sea urchin grazing.

Site Selection Criteria:

The experiment was conducted at 7–10 m depth on rocky reef at Lords Bluff, situated at the northern extremity of the Mercury Passage on the east coast of Tasmania. At this site, a large Heliocidaris erythrogramma barren was found adjacent to reef dominated by a diverse assemblage of native canopy-forming species including the common kelp Ecklonia radiata and the fucoids Phyllospora comosa, Carpoglossum confluens and Seirococcus axillaris.

Cause Of Decline:

C. amentacea var. stricta and C. compressa form complex communities providing habitats for numerous epiphytic species and shelter for many shade-loving organisms. For decades, the Region Provence-Alpes-Cote d’Azur’s coastline (France) has been exposed to water pollution and many studies have reported severe degradations or even disappearance of Cystoseira popula. Despite the setting up of a wastewater treatment plant in the vicinity of the Marseille sewage outfall 8 years ago, C. amentacea var. stricta has still not recolonised its former habitat.

Key Reasons For Decline:

Overgrazing

Scientific Paper

Persistence of sea urchin (Heliocidaris erythrogramma) barrens on the east coast of Tasmania: inhibition of macroalgal recovery in the absence of high densities of sea urchins

J.P. Valentine, C.R. Johnson
Botanica Marina, Vol. 48.
https://doi.org/10.1515/bot.2005.025

Organisation:

University of Tasmania

Site Observations:

Observation Date

8th Jan 2000 – 9th Jan 2001

Action Summary:

Paving blocks were deployed in a dense algal bed adjacent to a sea urchin barren. These blocks were then translocated to plots on the barren from which sea urchins were removed, and survival rates of recruits were measured.

Lessons Learned:

In sheltered and semi-exposed bays on the east coast of Tasmania, sedimentation appears to play a critical role in inhibiting early developmental stages of native macroalgae, thereby contributing to a positive feedback that acts to maintain the barren habitat.

Project Outcomes:

Transfer of paving blocks to plots in the barren where sea urchins were removed resulted in 80% mortality of recruits after three months, and 100% mortality after seven months. This was associated with an increase in the cover and depth of sediment. While sea urchins are undoubtedly important in creating urchin barrens, these results suggest that other mechanisms can influence recovery of native canopy species, such as sedimentation.

Nature of Disturbance:

The decline in macroalgal recruits on paving blocks transplanted to the urchin barren was associated with an increase in the cover and depth of sediment. A persistent cover of sediment also developed on paving blocks deployed on the urchin barren, where no native canopy-forming algal recruits were observed.

Key Reasons For Decline:

Overgrazing

Indicator Data:

Indicator:

Ending Value:

Starting Value:

Kelp Cover

0.0000
%
62.6794
%
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