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Corals are small animals that form a symbiotic relationship with algae. The algae produce sugars for the corals and are in turn provided with needed nutrients and protection from predators.

That's all great, but it doesn't explain where the amazing diversity of fish, mollusks, crustaceans, everything else comes from. As far as I can tell, the whole point of the coral's success is that their hard skeleton protects them from all but the most specialized predators.

So if the corals don't directly add (much) energy input to the coral reef ecosystem, what is it that makes the reefs so productive and diverse? Or, put another way, what makes a coral reef environment more productive than simple phytoplankton floating in the open ocean?

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One role of corals is to provide structure that offers protection from predation to many prey species as well as larvae and hatchlings. Reefs also provide relief from strong currents which, again, afford protection. Many other critters such as sponges, tunicates and other sessile animals use the reef as a substrate for attachment.

Don't be fooled by the apparent inedibility of coral, many fish eat it, notably Parrotfish. To give an idea of the extent of this activity, the bleached white beaches in Palau are carbonate "sand", not silica. They are the product of millenia of Parrotfish activity on the coral. (I don't have a link, this knowledge is courtesy of the Oceanic Society guide on our snorkeling trip.) In addition to Palau, I've snorkeled Indonesia, Honduras, Hawaii and elsewhere. In every venue, multitudes of many species of Parrotfish were to be seen aggressively chomping away at coral.

Also, the reef is also a substrate for many algae which serve as a food for other varietiesw of fish. Many of the coral inhabiting algae wouldn't be recognized as such looking like bubbles, fans and other oddities unlike common kelp.

Other species also feed on coral including welks, fireworms, nudibranchs and some starfish. Here's a link:http://infolific.com/pets/coral-reef-life/eating-the-coral-reef/

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  • $\begingroup$ So I was aware of the parrotfish, and I get that the shelter is a plus. But do you have other examples of fish that eat the coral? How do you get from coral to the incredible diversity of sea lillies, nudibranchs, and all the other various non-coral eating organisms? What is the food source? $\endgroup$ – kingledion Jan 14 '17 at 22:14
  • $\begingroup$ @kingledion. I've added to my post. Sorry, I was a tad rushed before having forgotten about coral as an algae substrate. $\endgroup$ – bpedit Jan 14 '17 at 23:12

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