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Recovery of canopy-forming macroalgae following removal of the enigmatic grazing sea urchin Heliocidaris erythrogramma
Citation
Ling, SD and Ibbott, S and Sanderson, JC, Recovery of canopy-forming macroalgae following removal of the enigmatic grazing sea urchin Heliocidaris erythrogramma, Journal of Experimental Marine Biology and Ecology, 395, (1-2) pp. 135-146. ISSN 0022-0981 (2010) [Refereed Article]
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DOI: doi:10.1016/j.jembe.2010.08.027
Abstract
The sea urchin Heliocidaris erythrogramma (Valenciennes, 1846) is considered an ecologically important
member of shallow sub-tidal reef assemblages across temperate Australia. However, defining its ecological
role has remained elusive due to a paucity of evidence demonstrating the ability of this species to graze and
maintain sea urchin barrens. Here we present critical evidence for a grazing effect of H. erythrogramma at
typically observable densities (~4–6 individuals m−2) by demonstrating recovery of canopy-forming brown
algae following two controlled removals of the sea urchin from ostensibly barrens reef at sheltered locations
in eastern Tasmania. 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, based on percentage cover community data, was observed
for only one location at 24 months post sea 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. The relatively slow and highly variable rates of algal recovery
across plots suggests that seasonal coexistence of annual (chiefly filamentous algae) and some perennial
macroalgae on H. erythrogramma barrens is likely due to a relatively low and variable intensity of selective
grazing. We conclude that 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. In
contrast, H. erythrogramma occurring on exposed Tasmanian reefs achieves similar densities but here barrens
are not observed and the sea urchin occurs cryptically within crevices and, consistent with experiments
elsewhere in Australia, the sea urchin under these conditions appears to feed exclusively on an abundance of
detached ‘drift’ macroalgae. Top–down and bottom–up factors leading to increased abundance of H.
erythrogramma will be important in determining the potential influence of this enigmatic grazer on rocky reef
communities, however critical tests of mechanisms controlling the switch between foraging modes are
needed. Taken together, correlative patterns and results of experimental removals across the range of H.
erythrogramma demonstrate that models of temperate Australian reef dynamics must account for the highly
context-dependent effects of sea urchin foraging.
Item Details
Item Type: | Refereed Article |
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Keywords: | Community dynamics, Habitat-modifying species, Kelp beds, Temperate Australian reefs, Urchin barrens, Wave exposure |
Research Division: | Biological Sciences |
Research Group: | Ecology |
Research Field: | Community ecology (excl. invasive species ecology) |
Objective Division: | Environmental Management |
Objective Group: | Coastal and estuarine systems and management |
Objective Field: | Rehabilitation or conservation of coastal or estuarine environments |
UTAS Author: | Ling, SD (Dr Scott Ling) |
UTAS Author: | Sanderson, JC (Dr Craig Sanderson) |
ID Code: | 68231 |
Year Published: | 2010 |
Web of Science® Times Cited: | 43 |
Deposited By: | IMAS Research and Education Centre |
Deposited On: | 2011-03-10 |
Last Modified: | 2012-05-21 |
Downloads: | 0 |
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