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Are there experiment showing the importance of density of sea urchin for the herbivory on macroalgae ? 

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Experimental studies have highlighted the significance of sea urchin density in influencing herbivory on macroalgae. Research conducted in various locations such as Moorea, the U.S. Virgin Islands, and the inner Seychelles has demonstrated that sea urchins, particularly Diadematid species, can have varying impacts on macroalgal control based on their densities. While some experiments indicate that moderate increases in sea urchin densities may not significantly reduce macroalgal stands , others show that natural densities of sea urchins can help maintain coral health by controlling algal-sediment accumulation and promoting coral survival . Additionally, the feeding preferences of sea urchins, like Diadema antillarum, for different macroalgae species have been studied, revealing selective feeding behaviors that can influence coral reef ecosystems . These experiments collectively emphasize the intricate relationship between sea urchin density and herbivory on macroalgae in coral reef environments.

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The research paper demonstrates the significant impact of sea urchin density on herbivory by showing that natural urchin densities maintain coral health by controlling algal-sediment accumulation.
Not addressed in the paper.
Yes, experiments in the inner Seychelles showed that higher sea urchin densities led to a moderate reduction in macroalgal cover, indicating the importance of sea urchin density for herbivory on macroalgae.
Increased sea urchin density did not significantly impact macroalgae covers in Moorea's lagoon. Moderate diadematid densities alone may not reduce macroalgal stands without other herbivore guilds.
The study highlights the importance of sea urchin density in herbivory on macroalgae, indicating their selective feeding preferences and potential impact on coral reef ecosystems.

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