Why Coral Reefs Have So Much Biodiversity
Understanding Nutrient Cycles and Darwin's Paradox
Jul 8, 2009
Coral reefs are well known as hot spots of biodiversity surrounded by large schools of colorful fish, gliding rays, and scuttling mollusks. However, the clear blue waters that coral reefs inhabit do not contain many nutrients – hence the water’s clarity. That one of the world’s richest ecosystems live in such a nutrient poor area is known as “Darwin’s Paradox”. Yet there is a reason that corals and so many species came to evolve in the ocean’s crystal clear waters. The reason comes down to efficient nutrient cycling.
The Coral Reef Food Web
Stanford University writes in its Microdocs article “Species on Coral Reefs” that there are between 1 and 9 million species living on coral reefs. Although coral reefs cover less than one-tenth of the world’s ocean, they are home to more than one-fourth of all marine species. This vast number of species leads to the existence of many intricate food webs with big fish eating little fish that eat smaller shrimp and so on. However all food webs eventually come down to producers – on land, plants use sunlight and nutrients from the soil to feed many animals. On the reefs, the major producers are corals’ symbiotic algae.
Coral Reefs Recycle Nutrients
Producers in coral reefs include phytoplankton drifting through the water column and the corals’ algae. The phytoplankton and algae are both photosynthetic organisms that use sunlight to power carbon fixation. Fish and crustaceans eat the phytoplankton and thus pass along nutrients throughout the food web. The algae pass on nutrients to their corals. Another important organism in the nutrient cycle is cyanobacteria which fixes nitrogen. Elizabeth Wilson writes about the bacteria in the August 16, 2004 article “Coral’s Symbiotic Bacteria Fluoresce, Fix Nitrogen” for Chemical and Engineering News. Nitrogen is a vital nutrient that most organisms need to live.
The Importance of Sponges to Coral Reef Biodiversity
A study done in 2001 reports that sponges may be the key to solving Darwin’s Paradox. John Roach of National Geographic discusses this study in the November 7, 2001 article “Rich Coral Reefs in Nutrient-Poor Water: Paradox Explained?” A team of researchers studied sponges in the Red Sea and found that a variety of sponges live in the crevices of the Red Sea’s reefs. These sponges are efficient filter feeders consuming roughly sixty percent of the phytoplankton drifting by. The sponges then excrete the nutrients gained from the phytoplankton, for corals to use. Some scientists take this finding with a grain of salt and say much more research needs to be done to truly explain Darwin’s Paradox.
Coral Biodiversity and Darwin’s Paradox
The final answer behind coral reef’s rich biodiversity may still be unknown. However as researchers continue to study the organisms on the reefs they come closer to resolving Darwin’s Paradox. Understanding the biodiversity of coral reefs is important as people rely on reefs for a variety of functions. The massive food webs that coral reefs support help feed millions of people every day.
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