Sometimes the Corals Fight Back

During my semester abroad, I had the pleasure of scuba diving the Great Barrier Reef. Not only was it one of the most humbling experiences of my life, it was also intellectually stimulating. The corals on the reef are very densely packed together in what could be described as “forests” of corals. Although the reefs may look peaceful and calm, there is a war raging at all times.


All animals have some sort of competition for resources between themselves and other species. For corals, it is not as pronounced as, say, a male lion scaring off other males. However, corals fight for resources just like any other animal. The biggest resource they scavenge for is sunlight. The sunlight provides energy for their endo-symbiotic partners, their zooxanthalae. Without sunlight the corals may grow much slower, or even die. They also fight for space in the water column to feed, as well as physical space to grow.

Corals have two forms of competition: direct and indirect. Indirect competition is simply competition without actual physical contact. Some corals have evolved to grow very rapidly, and in this way simply grow over or faster then their neighbors. In this way they can out-shade their competition and monopolize the sunlight in the area. Direct competition is competition with contact. A common method of direct competition is to fling out tentacles with nematocysts, stinging cells often filled with toxins, to destroy their opposition. Other corals can also release deadly mucous into the water column. They can even release polyps that act as carriers to deliver painful or fatal stings from nematocysts. Indirect competition is often the safer option for coral, as they do not come in contact with other coral. However, it is much slower since the coral has to physically outgrow other coral. Direct competition is faster but it puts the coral in question in danger from a counterattack as well.

It was astounding to see all of the amazing coral in person. It was even more astounding to understand that the coral I was observing might be waging a slow, silent war as I glided over them.

-Patrick Rex

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