How do sea urchins affect coral reefs and sea-grass beds?

Sea urchins play a complex role in marine ecosystems, acting as both destructive forces and essential regulators depending on their population density and environment.

• Coral Reefs: Certain tropical sea urchins are vital for the health of coral reefs. By grazing on and controlling the growth of seaweed, they prevent algae from overgrowing and smothering the coral, which allows the reef to flourish. If these urchins are removed, seaweed can proliferate, leading to the degradation of the reef habitat.1
• Sea-grass Beds: In contrast, when sea urchin populations become excessively large, they can devastate sea-grass beds in tropical regions. This overgrazing negatively impacts the various organisms that rely on these beds for shelter and sustenance.1

Beyond these specific impacts, sea urchins also contribute to the physical environment; those that burrow into rocks or along shorelines can accelerate the erosion of those areas.1