It's amazing if you think about it: In some parts of the ocean (usually tropical), the plankton is so thick that some animals can anchor themselves to a rock and spend their whole lives grabbing dinner whenever they feel like it, never moving from one spot.   Even more amazing, quintillions of such creatures can colonize an area, and live the good life over thousands, if not millions, of years!

Over time, the protective stony shells excreted by colonies of coral polyps, hydrozoa, bryozoa, and sponges build up into massive formations of a limestone-like substance.  To geologists, it is an important process forming sedimentary rock1. More importantly to oceanographers, marine biologists, and almost everyone else, the most beautiful and diverse type of ecosystem in the world, not to mention the most wild and woolly laboratory for evolution that ever existed, develops around a coral reef.

A list of the wonders of a coral reef ecosystem would stretch forever: Creatures from thousands of species congregate around the reef, competitors for the rich broth of plankton, predators of the coral or their egg capsules, predators to the predators, scavengers on the detritus from the ruin of battle.  Specialized ecological niches, parallel evolution, symbioses, and opportunities for parasitism are everywhere. Fish are so thick that sea anemones anchor themselves to the rocks in the same way as corals, and pick off fish without having to budge.  Other fish use the sea anemones as a refuge from predators, occasionally bringing in a meal for their hosts. Colors abound as grazing creatures announce their toxicity to would-be predators.


The coral reef cycle was first articulated by Charles Darwin and the patriarch of geomorphology, William Morris Davis:

  • Coral polyps not only consume plankton, they are part of the plankton before they settle down.  Thus, larval coral polyps are spread throughout the oceans.  Eventually, the larvae find a place to anchor themselves. Sometimes this is a new area without a reef, such as the shallows along the coast of a volcanic island recently emerged from the ocean.
  • Over millennia, the corals build fringing reefs hugging the coastline.
  • Meanwhile, land erosion due to rainfall, as well as coastal erosion due to wave action, erodes the island.  Unlike the land, the reef can renew itself.  Inside the reef there is less plankton, and coral doesn't grow as fast there.  The reef becomes separated from the shoreline, creating a barrier reef, with a lagoon separating the reef from the shore. The largest coral reef in the world, the Great Barrier Reef, parallels the coast of Australia for 2000 kilometers (1200 miles).
  • A barrier reef will protect the shoreline from the worst of the ocean's waves, but erosion will still occur. Eventually an island with a barrier reef ringing it is eroded completely away, leaving an atoll.

This description, although adequate for the time, has proven to be too simplistic; things are far more complex.  Other processes complicate the development of coral reefs.  The subsidence of the sea floor as it moves away from tectonic spreading centers drives coral reef growth. Sea level change is known to affect the cycle: As sea level rises, the land is drowned, but the reefs have room to grow. However, it is a race between the sea and the reef: If sea level rises too quickly, the zone where the all-important plankton grows can rise completely above the reef, drowning it.  When sea level falls, reefs are left high and dry, and new areas become shallow enough for the whole cycle to begin again. This, and caldera-forming volcanic eruptions, most likely hasten an island's development towards an atoll.

Predation of the coral can serve to keep the reef in trim, but can also destroy it. The most intriguing predator of coral, and the most important recycler of coral reefs, is the parrot fish.  Parrot fish use their hard beaks to bite of chunks of coral, and grind it up to extract the yummy coral polyps inside.  They then excrete the sandy bits that are left; most of the coral sand on the bottoms of lagoons, or on the beaches, has passed through a parrot fish in this manner.  A well-known recent opportunist, the Crown-of-thorns starfish, has been wreaking destruction of the coral reefs off the coast of California.  Human predators also exist: Methods of harvesting tropical fish in the Philippines are extremely destructive.

Climate change and anything else affecting the location of the plankton zones will also affect the reef.   Over the past  decade or so, scientists have become increasingly worried as coral reefs die off with no good explanation.  Global warming and pollution have been blamed but no clear link has been demonstrated.  What is clear is that something is unraveling the unimaginably complex fabric of ecological dependencies that make coral reefs possible, rendering their bewildering beauty into wasteland.


1Entire mountain ranges, such as the Guadeloupe Mountains of southwestern New Mexico, are made of coral.

        In recent years, human activities resulting in the overharvesting and pollution of coral reefs have taken a great toll on coral ecosystems. Destructive fishing practices contribute greatly to the failure of coral ecostystems to function. Overfishing leads to the lack (and in some cases extinction) of essential links in the food chain resulting in the starvation of organisms on the higher end of the chain and the overpopulation of organisms on the lower end.

Methods such as expelling cyanide into fishing waters to stun a potential catch not only affects the fish to be caught but all of the organisms living nearby the catch site. Chemicals like cyanide cause paralyzation of fish and marine organisms as well as coral bleaching. The pollution of coral ecosystems is also largely responsible for the degradation and deterioration of coral ecosystems. The direct disposal of hazardous waste (whether it be trash, bottles, oil or radioactive material), in the ocean is the greatest cause of reef deterioration.

Also responsible is the lack of the presence of coastal mangroves, whose roots hold soil in place, therefore minimizing sediment runoff during storms. Mangroves also play an important role in the exchange of oxygen and carbon dioxide between the reefs and the air, providing an oxygen-rich environment in which marine organisms thrive.

The recreational utilization of coral ecosystems also harms the reefs. Illegal sport fishing is a great problem for coral reefs due to the removal of necessary aspects of coral systems, such as sharks being poached for their dorsal fins. Also, the harvesting of coral, fish, shells and plant life as to be used in pet aquariums or for souveniers inhibit’s the system’s ability to function properly as one thriving unit.

These problems may seem distant, but they are in no way insignificant.



        The deterioration of these coral systems not only affects the surrounding marine life, but the stability of surrounding human life as well. In Jamaica, almost all reefs are dead due to overfishing by commercial boats satisfying the needs of ritzy, five-star restaurants in wealthy countries, but causing famine among the country’s inhabitants.

This corruption of the coral systems deprives coastal villages not only of fish to eat, but also of natural resources only harvestable in the presence of the coral reef. And although it is seemingly insignificant, from the perspective of a well-to-do country, what people do not realize is that a great lot of the earth’s population live in third-world countries where food and resources are scarce. There is no justification in the upper class’ living frivolously at the expense of the poverty and starvation of those who are not so lucky.

Reefs also provide resources needed to produce prescription drugs to the modern world and are a valuable resource when it comes to finding cures for diseases. Today, billions of people are dying of incurable diseases having yet to be cured (HIV/AIDS, cancer, leukemia, etc.) whose remedies are believed to rest in the ocean.

Are these priceless sites worth losing, at the cost of possibly salvagable lives, simply so that the unreasonable demands of commerce and recreation are satisfied? Today’s economy is one which thrives on the pleasure and leisure of the people fueling it, but if we do not watch our consumption of the earth, these standards may find themselves less than possible. Coral ecosystems not only provide food and medicine to this modern society, but also support tourism, the production of cosmetics, textiles and many other aspects of the economy, but by overutilizing the resourcefulness of the coral reefs, people will find themselves confronted with a dead end of the modern leisure that they so enjoy. Although seemingly unlikely, humans depend greatly upon coral reefs to provide them with many things they take for granted; a problem which must be resolved with urgency if people expect the environment to continue to support them with its resources.

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