The fore reef zone (also often called the “reef front” or “reef face”) begins at the seaward base of the reef crest zone. Here the sea floor begins to slope downward somewhat gently at first and then ever more steeply. Two distinctly different segments (sub-zones) of the fore reef are often recognized, simply called the “upper” and “lower” portions.
This part of the fore reef zone begins immediately seaward of the reef crest. It is characterized by a comparatively gentle downward slope and the frequent presence of branching corals.
Wave energy is high at the base of the reef crest, so the uppermost portion of the fore reef is 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.) rapidly increases. This deeper part of the upper fore reef sub-zone contains the highest coral species diversity and greatest variety of hard coral colony forms to be found in the entire coral reef ecosystem. Most typically, this “upper” portion of the fore reef extends from about 3-15 meters in depth, but it is not uncommon for the upper section to reach depths of 20 meters.
Deeper yet, the “upper” fore reef sub-zone gives way to the “lower”, where branching corals become far less frequent and massive coral forms become dominant. Eventually, massive forms become less prevalent and the reef becomes dominated by plate-like coral forms best adapted to take advantage of the minimal sunlight present at greater depths.
The lower part of the fore reef zone extends from the margin of the upper segment into waters too poorly lit to permit coral growth. In many cases, the lower fore reef plunges abruptly to great depths, creating formations popularly known to scuba divers as “walls”.
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