There's no doubt that the Great Barrier Reef is one of those landmarks people refer to as a single entity (like a mountain or a historic building). What people actually see is a collection of living architectural structures, spanning thousands of kilometers along the coastline of Queensland, northern Australia. In fact, the reef is composed of thousands of separate reefs and islands that vary dramatically along their length. To understand what I mean by "varies," consider that if you were to visualize the entire reef as one long stretch, you'd be missing what makes the Great Barrier Reef such a fascinating environment: the reef is a mosaic of broken-up spaces -- including various types of habitats, lagoons, channels, and gaps.

Most people refer to "the reef" as being constructed from coral polyps, tiny animals that construct hard skeletons over time through the accumulation of these skeletal remnants. These skeletal foundations then support a diverse array of ecosystems, giving the appearance of being overcrowded with life. Some examples of species that make themselves at home among the maze of ridges and crevices include fish, rays, sharks, sea turtles, clams, sponges, sea stars and countless other species that people rarely learn about. This is not merely a visually appealing setting for scuba divers -- it's a complex ecosystem where the structure and integrity of the coral directly impacts how it feeds, provides shelter, and breeds.

One other aspect of coral is equally significant, yet somewhat obscure: each coral polyp has a symbiotic relationship with algae that live within the coral itself. These algae produce energy for the coral, and in return receive protection. As such, the presence of these algae enables corals to thrive in clear tropical waters lacking in nutrients. The overall efficiency of this system is dependent upon both sides of the relationship, and as such is quite delicate. When the water reaches an elevated temperature for extended periods of time, the coral becomes stressed and begins to expel the algae. At this point, the coral appears white/pale due to the absence of the algae producing the colors. While the bleached coral may not die immediately after losing the algae, it will be weakened and in a state of distress. The loss of these algae is known as coral bleaching. However, repeated or prolonged events of coral bleaching can ultimately lead to the death of the coral.

The Great Barrier Reef is also influenced by unseen forces (or events) that do not appear apparent when viewing photographs. Currents transport larvae from one reef to another creating a network of invisible pathways. Storms can damage the coral and break it into smaller pieces that could potentially serve as the foundation for new coral growth depending upon where these pieces settle. Predation plays a role as well, specifically the crown-of-thorns starfish, a spiny creature capable of consuming coral. When conditions favor the crown-of-thorns starfish and its populations increase rapidly, it can cause widespread destruction of coral, resulting in a reef that appears healthy from afar, however, the majority of its living coral cover has been destroyed.

There is also a human component to the Great Barrier Reef. The Great Barrier Reef is an integral part of Australia's natural heritage and a key driver of tourism in Australia. Many coastal communities view the Great Barrier Reef not as an environmental issue, but as a source of employment, commerce, and lifestyle. Both fishing and shipping occur within the boundaries of the Great Barrier Reef and the challenge lies in finding a balance between utilizing the reef and protecting it. Management has attempted to zone areas of the reef to restrict certain activities and there are currently ongoing initiatives to improve water quality through reduction of land-based pollutants, such as sediments and fertilizers, since pollution originating in rivers can travel downstream and affect the reef.

Water quality may seem uninteresting unless you recognize how closely related everything is. During periods of heavy rainfall, rivers can carry sediment, fertilizers, and pesticides down stream and out to sea. Sediments can reduce sunlight necessary for coral growth by clouding the water, while excessive nutrients can stimulate the growth of algae competing with corals for space. While neither of these represents immediate, dramatic threats (such as a shipwreck), they represent gradual increases in stress that can continue to build over time. When a reef is already under stress due to increased water temperatures, the additional pressure exerted by sediment and nutrient-rich runoff reduces the reef's ability to recover from disturbances.

Climate change is the larger-scale context that complicates all of the above factors. Reefs can recover from storms, local outbreaks of predators, etc., provided the underlying conditions remain favorable. Recovery is an essential part of the history of reefs -- reefs are dynamic systems that do not exist in a static state. However, when frequent high-temperature events occur and the average ocean temperature continues to rise, the opportunities for recovery decrease and begin to resemble a constant push rather than a temporary setback. Therefore, the urgency surrounding the Great Barrier Reef stems largely from the need for time to preserve the reef's resiliency, and climate warming is essentially removing time from the equation.