What is Coral?

What is coral? Just hearing that phrase can conjure up many different images in ones mind. images of beautiful oceanic rain forests or or white skeletons that sit on a shelf in grandma’s living room. Half plant and half marine organism, corals are the result of hundreds of millions of years of evolution. As small as a single polyp that can just barely be seen with the naked eye or as large as the great barrier reef which stretches over 1300 miles, corals amaze us and at the same time teach us about how the climate and marine environments evolved into that we see today.

The Nature of Coral

At the most simple level, corals are comprised of a tissue, polyps, and sometimes a skeleton. The tissue contains unicellular flagellate protozoa of the genus zooxanthellae which undergo photosynthesis and provide food for the coral.  These Zoox as they are called are what give corals their stunning colors.  The coral tissue in turn uses the energy from photosynthesis for growth and other biological functions.  In some corals, this tissue surrounds a calcium carbonate skeleton.  These skeleton secreting corals or Scleractinian corals come in many shapes and sizes ranging from large branches to ball shaped mounds to encrusting plates. The goal of these shapes is to compete for light as well as to maximize surface area for feeding and nutrient exchange with the surrounding sea water.


Coral distribution

The majority of coral species are found in warm, nutrient poor tropical waters sandwiched between the tropic of cancer and capricorn(23 degrees north and south latitude). Yet, as we learn more about the vast expanses of the oceans, we are finding that corals are actually not confined to tropical waters as was once thought.  We are also learning that they can grow many hundreds of feet deep in almost complete darkness. The basics biology we spoke of where corals use the sun’s light for the majority of their energy, and secrete a skeleton to reach toward this energy source,  seems to be more of a sliding scale rather than a hard and fast rule.  A deeper coral may have more exaggerated polyp features which can be used to maximize prey capture.  While corals in shallow water may have relatively smaller polyps and have a bright color which acts as sunblock to protect the coral from UV rays.  It is these curious facts that we are learning which makes corals and coral reef research such an interesting topic.

photo courtesy of NOAA

An uncertain future

It seems an unsettling reality that an organism as diverse and as able to adapt as corals is being impacted as heavily and as quickly as we are witnessing in the last 40 years or so. The fact that corals have been on this planet for as long as they has is a testament to their ability to readily adapt to their environment through hundreds of millions of years of climate changes, mass extinctions, and predation.  As of late though, our impacts on the worlds oceans both direct and indirect have summoned up a toxic trifecta of impacts that are happening so quickly on an evolutionary scale, that they are  proving harmful to many of the worlds reefs.  In the last 30 years alone, we have lost over 10% of the worlds reefs. Add to that an accelerated rate of bleaching events caused by various man made factors, and you have a very bleak outlook for the worlds reefs unless actions are taken to reverse the conditions.