Concerning Corals

by Jean Kenyon and Erin Looney
photos by Benjamin Richards and Jason Helyer

Stony corals (Class Anthozoa, Order Scleractinia) are marine invertebrates that secrete a calcium carbonate skeleton.  Stony corals can be hermatypic (significant contributors to the reef-building process) or ahermatypic, and may or may not contain endosymbiotic algae called “zooxanthellae”.  The largest colonial members of the Scleractinia help produce the carbonate structures known as coral reefs in shallow tropical and subtropical seas around the world.  The rapid calcification rates of these organisms have been linked to the mutualistic association with the zooxanthellae, found in the coral tissues.  Massive and branching stony corals are the major framework builders of shallow tropical reefs.  Some stony corals occur in deep water and are azooxanthellate (they do not contain zooxanthellae), but these deep water corals typically do not form extensive reefs. Corals are arguably one of the most important components of the coral reef system, providing substrate for colonization by benthic organisms, constructing complex protective habitats for myriad other species, including commercially important invertebrates and fishes, and serving as food resources for a variety of animals.

While at Johnson Atoll we are collecting data on corals that will tell us more about species abundance and distribution, size class distribution, and disease.  Each site we visit differs in terms of species dominance, the relative abundance of coral, and the health of the corals present.  Many factors contribute to this, including the location of the reef (whether it is a backreef, forereef, or in a lagoon), wave intensity, and its closeness to human population and associated pollution.  One would expect that reefs as far removed as Johnston would be pristine, healthy, flourishing environments, but even these are subject to disturbances such as hurricanes, marine debris, and pollutants introduced to the environment throughout history.  Especially in the Pacific, many island which are not currently inhabited, have had sizable human populations in the past. Johnston is one of these and, we find a relatively high prevalence of coral disease at Johnson Atoll compared to other islands.

Although these reefs may not be as pristine as we might hope, they are by far some of the most beautiful and deserve our best efforts in understanding the dynamics that keep them thriving. Every day we are amazed by something new, something we've never seen before (possibly that no one has seen before), and are reminded of why we are out here, trying to learn more about this complicated and amazing environment.