Why are cnidarians especially diverse in tropical waters?

Cnidarians are most abundant and diverse in tropical waters, where they play a fundamental role in building the frameworks of reefs and atolls.1

Their high diversity in these regions is closely linked to their ability to form mutualistic symbioses with unicellular algae known as zooxanthellae. These algae provide essential benefits that allow reef-forming corals to develop more substantial skeletons than those that lack such associations. Because these corals are highly dependent on their algal partners, they thrive specifically in the shallow, well-illuminated waters characteristic of tropical environments.2

Beyond these symbiotic relationships, the structural complexity provided by their calcareous skeletons creates diverse habitats that support a wide array of marine life, further contributing to the ecological richness of tropical seas.31