What marine ecosystem is known for being the equivalent of rainforests in terms of biodiversity?

Coral reefs are often referred to as the "rainforests of the sea" due to their extraordinary levels of biodiversity. They provide a complex habitat that supports a wide array of marine life, including thousands of species of fish, invertebrates, and other organisms. This high diversity is supported by the structure of the reef itself, which offers numerous niches for different species to thrive.

In addition to their variety of species, coral reefs play a critical role in the health of marine ecosystems. They contribute to coastal protection, support fisheries, and provide resources for many communities. The intricate relationships among the species in coral reefs, along with their capacity to adapt and foster diverse communities, solidify their analogy to terrestrial rainforests, which are also hotspots of biodiversity. Other ecosystems listed, while important in their own right, do not match the incredible biodiversity typically found in coral reefs.