What term describes the puzzle of reefs thriving in nutrient-poor tropical waters?

The puzzle of reefs thriving in nutrient-poor tropical waters is called Darwin’s paradox. Tropical seas often contain little dissolved nitrogen and phosphorus, yet coral reefs can be among the most productive and diverse ecosystems on Earth.

The paradox is named for Charles Darwin, whose 1842 work examined coral reefs and their distribution. The modern ecological question is not mainly about how atolls form; it asks how reefs sustain high biological productivity despite apparently infertile surrounding water.

One major explanation is efficient nutrient recycling. Corals live in close partnership with photosynthetic dinoflagellates, commonly called zooxanthellae, which provide organic energy while receiving nutrients and shelter. Reefs also retain and reuse material through food webs involving algae, plankton, sponges, fish, and invertebrates.

Corals can absorb nutrients directly and capture zooplankton with their tentacles, especially at night. Pollution and excess nutrients can still damage reefs, so “nutrient-poor” does not mean reefs are immune to human-caused enrichment or decline.