Ling, SD and Reeves, SE and Kriegisch, N, Octocoral barrier to grazing sea urchins allows macroalgal recovery on barrens ground, Journal of Experimental Marine Biology and Ecology, 524 Article 151292. ISSN 0022-0981 (2020) [Refereed Article]
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Experimental exclusion of marine herbivores is a powerful approach to reveal their effects on the structure and function of ecosystems. However, such manipulations can be logistically challenging, particularly for subtidal reef systems. Here we report novel observations of a natural barrier to grazing sea urchins formed by the octocoral Erythropodium hicksoni (Family: Anthothelidae, Utinomi, 1971), which allowed localised growth of standing macroalgae on barrens ground despite sea urchin (Heliocidaris erythrogramma) densities locally exceeding 40 individuals m−2. Effectiveness of the octocoral barrier was experimentally tested by cutting 200ámm by 200ámm plots within the centre of octocoral colonies (providing clean reef surfaces completely enclosed by octocoral), which were otherwise surrounded by sea urchin barrens. Within 1ámonth, macroalgae completely colonised reef surfaces inside octocoral plots, which continued to proliferate over 12ámonths relative to background barren ground plots. Furthermore, a procedurally-controlled experiment (whereby barren control plots were also scraped clean of all biota to the same dimensions as octocoral plots), revealed octocoral-barriers to again exclude urchins and enable greater recovery of macroalgae relative to the procedural-control. In all octocoral plots, algae grew to the octocoral edge, indicating a lack of allelopathic/ shading effects by octocoral, which forms a thin encrusting veneer over reef surfaces <20ámm height. However, octocoral regrew to infill the excised portion of the colony at a mean rate of 0.23ámmá▒á0.01SE day−1, which was routinely trimmed to maintain original plot dimensions. Competition for space between octocoral and macroalgae was also evident when recovered macroalgae overhung octocoral barriers and scoured surrounding octocoral. Results demonstrate the existence of natural biological barriers to grazing urchins, which can be utilized to efficiently replicate experimental exclusions, taking only ~10ámin to construct per plot. While bio-chemical/physical mechanism(s) of the barrier were not determined, the potential for such biological barriers to form important local refugia for macroalgae and applications over larger scales remains largely unexplored.
|Item Type:||Refereed Article|
|Keywords:||gorgonian coral, erythropodium, herbivory, biological control, seaweed, kelp bed communities, temperate reef, grazing, octocoral, growth|
|Research Division:||Biological Sciences|
|Research Field:||Community ecology (excl. invasive species ecology)|
|Objective Division:||Environmental Management|
|Objective Group:||Coastal and estuarine systems and management|
|Objective Field:||Control of pests, diseases and exotic species in coastal and estuarine environments|
|UTAS Author:||Ling, SD (Dr Scott Ling)|
|UTAS Author:||Reeves, SE (Mr Simon Reeves)|
|UTAS Author:||Kriegisch, N (Ms Nina Kriegisch)|
|Funding Support:||Australian Research Council (DP170104668)|
|Deposited By:||Ecology and Biodiversity|
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