The reef face zone (also often called the “fore reef” or “reef front”) begins at the seaward base of the reef crest. Here the sea floor begins to slope downward somewhat gently at first and then ever more steeply.
This zone contains the greatest mass and diversity of hard corals found in coral reef ecosystems. It also is home to the greatest number of coral reef fish species of any of the three major reef zones.
For these reasons, along with the zone’s extensive depth range and ease of access from the open sea, this is where most recreational coral reef scuba diving occurs. In many cases, the face plunges abruptly to great depths, creating formations popularly known to scuba divers as “walls”.
Two distinctly different segments of this zone are generally recognized, simply called the “upper” and “lower” portions.
The upper face begins immediately seaward of the reef crest. It is characterized by a comparatively gentle downward slope.
Wave energy is high at the base of the reef crest, so the very shallowest parts of the face are typically dominated by massive or encrusting corals that are more resistant to the destructive forces of wave impact.
As depth increases and wave energy abates, the frequency of branching corals (e.g., Acropora spp., Agaricia spp., Montastrea spp.) rapidly increases, along with boulder corals such as Diploria spp. It is here that we find the highest coral species diversity and greatest variety of hard coral colony forms to be found in the entire coral reef ecosystem.
Usually this “upper” portion of the face extends from about 3-15 meters in depth, but it is not uncommon for this sub-zone to reach depths of 20 meters.
Deeper yet, the “upper” face gives way to the “lower” segment, characterized by different dominant corals. This sub-zone extends from the margin of the upper face into waters too poorly lit to permit coral growth.
At first, branching corals become far less frequent and massive coral forms like Montastrea spp. dominate the hard coral assemblages. As depth continues to increase, branching forms become infrequent and massive colonies become less dominant.
Here, the relative abundance of plate-like coral colonies (e.g., Agaricia spp.) increases. These colony forms have larger surface areas relative to their total mass, and therefore are best adapted to take advantage of the minimal sunlight present at greater depths.
Eventually, diminished sunlight is insufficient to permit photosynthesis by the the corals symbiotic zooxanthellae, and hard coral growth ceases.
Get updates via email on all things coral.