GEOLOGICAL SCIENCES 100
CORAL REEFS MINI-COURSE
KYGER C LOHMANN

 
8.  Interaction of the Reef and the Physical Environment

Basic Concepts:

When one examines the distribution of coral forms and types, these directly reflect the energy distribution across the reef.  Below is a figure that summarizes many of the feature we described in class.   Keep track of what the energy is in each part of the reef:  Fore reef, Reef Front, Reef Crest, Reef Flat, and Back Reef.  Each of these subenvironments is characterized by unique energy and depth conditions.
 
 

Key Points to Remember:

In the deep ForeReef, Elkhorn develop as broad flat branched corals with their frond (branches) oriented subhorizontially to maximize the absorption of light.

As the energy increase up into the Reef Front, we see the Foundation corals, the massive head varieties dominating the corals types.  These are ornamented with branching Elkhorns whose branches become narrower,and thicker to withstand the greater forces exerted by the incoming waves.   One also finds flexible sea whips and fans growing in association with these corals.

Within this Fore Reef and Reef Front, because of the refraction of waves we see the development of spur and groove structures.  The spurs are finger like projections of the reef separated by valleys or grooves in which current actively move sediment up across the reef.

At the reef crest where the waves break,  the highest energies exist.  Here, only the strongest coral and encrustor types can persist.   A common form here is the firecoral (Millepora) which forms as interlocking honeycomb structures.

The Reef Flat is an area if high currents that result from the breaking of waves at the reef crest.  Here we find an interlocking framework of Elkhorn corals that have been encrusted by a variety of other forms that develop on and within the cavities between branches of the Elkhorn.

With the breaking of the wave energies, the Back Reef area is of lower energy.  Here, we see the fragile forms developed.  Quite common is the staghorn coral.  Also this area is dominated by debris that is washed over the reef flat during storms.   Therefore, the sediment accumulates in this area and is colonized by grasses.
 
 

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