Tag Archives: ocean

Coral Reef Ecosystems

From Bright and Bio-diverse to Blighted and Bleached. What are Coral Reefs, and why are they in Danger?

Coral Reefs are among the most productive ecosystems on the planet.  These wondrous undersea worlds are often referred to as ‘rain forests of the sea,’ a name that expresses their ecological complexity, their beauty, and their vulnerability.  But what exactly is a coral reef, and why are they in danger of destruction?

Coral Reef. Photo Courtesy of U.S. Fish and Wildlife Service/Flickr

The first time I saw a coral reef ‘up-close and personal,’ was on a snorkeling trip in the Florida Keys. The beauty of what I saw amazed me. I was eager to explore its nooks and crannies, and I was curious to know how it all got there.  My first question was: What exactly is a coral reef, and what exactly are corals?

I would soon get my answer.  I would also get a lot more information about coral reefs than I had asked. Through an impassioned, impromptu speech from a man who had grown up in the Caribbean, I learned of the destruction of the once beautiful coral reefs off the shores of his hometown. Solemnly, he told me of the remains of a reef that he used to swim at as a teenager.  The reef had once thrived, but now it sat seemingly life-less and abandoned on the seafloor.

In the past three decades, the world’s coral reefs have experienced unprecedented decline.  The trend is continuing.  Decline in coral reef health and coverage is caused by a number of factors; many of them inflicted by humankind.  Overfishing strips reefs of species that keep the ecosystem in balance; pollution from agricultural runoff brings toxins that can kill the coral; and hurricanes ravage and crumble the reef structure. On top of all of this, rising levels of carbon dioxide in the Earth’s atmosphere and oceans, may be the most significant threat of all. Rising sea temperatures and ocean acidification, both of which are linked to increasing carbon emissions, can have serious impacts on coral reefs.

The video below describes some of the most significant threats to coral reefs.

Coral reefs are extremely complex ecosystems: conglomerations of animals, minerals, algae, and other organisms, breaming with life and ecological productivity. What most of us see underwater and identify as ‘coral,’ is actually a colony of thousands upon thousands of tiny invertebrate animals (coral polyps) nestled together and built up upon the calcium carbonate (limestone) ‘skeletons’ of sometimes thousands of years worth of old coral colonies. Mollusks, young fish, sea turtles, and many others, seek food and refuge within the reef, so when coral reefs are destroyed, so are the habitats for all these other living things. But with this complexity and productivity comes vulnerability.

Even small changes in water temperature leave coral reefs vulnerable to a phenomenon called coral bleaching. Bleaching occurs when coral polyps under stress expel the algae that live symbiotically within them. When the algae are gone, the coral appears white, or “bleached,” because algae gives coral reefs their vibrant color.  Bleaching also leaves coral without a significant source of energy, energy from algal photosynthesis.  The stressed, bleached coral may become more susceptible to disease.

Coral Bleaching. Photo by Mark Spalding Courtesy of World Resources Institute/Flick

In their study, Coral Reefs & Global Climate Change, Robert Buddemeier et al., link the bleaching phenomenon to global climate change. They write, “Increases in ocean temperatures associated with global climate change will increase the number of coral bleaching episodes…While coral species have some capacity to recover from bleaching events, this ability is diminished with greater frequency or severity of bleaching. As a result, climate change is likely to reduce local and regional coral biodiversity, as sensitive species are eliminated.”

Ocean acidification, associated with increased atmospheric CO2 levels, may also seriously harm coral reefs. Acidification of the ocean will lessen the availability of carbonate ions in the water, according to the National Oceanic and Atmospheric Administration.  Corals need to be able to extract carbonate ions from the seawater in order to build their skeletons.

Sadly, coral reefs, with all their beauty and biodiversity, are among the first of many ecosystems to suffer the effects of climate change and increased carbon dioxide emissions. However, all hope is not lost. Efforts to protect and restore the world’s coral reefs are underway. Future blogs will discuss some of these efforts, in hopes of inspiring readers towards action.