concept

Darwin's paradox

The question Charles Darwin raised looking at coral reefs: how can one of the richest, most crowded ecosystems on Earth flourish in clear tropical seawater almost devoid of nutrients — water that should support very little life? The answer is retention and recycling: the coral–algae symbiosis locks nitrogen and phosphorus internally before they can leak away; sponges reclaim the dissolved carbon corals shed and return it to the food web; and the island or reef mass itself obstructs currents to generate local upwelling. The water is poor, but the reef lets almost nothing escape.