Shallow-Water Benthic Habitats of the Republic of Palau

Project Methods

Zone

Zone

Thirteen mutually exclusive zones were identified from land to open water corresponding to typical insular shelf and coral reef geomorphology (Fig. 1-3). These zones include: shoreline intertidal, vertical wall, lagoon, back reef, reef flat, reef crest, fore reef, bank/shelf, bank/shelf escarpment, channel, dredged (since this condition eliminates natural geomorphology), unknown, and land. Zone refers only to each benthic community's location and does not address substrate or cover types within. For example, the lagoon zone may include patch reefs, sand, and seagrass beds; however, these are considered structural elements that may or may not occur within the lagoon zone and therefore, are not used to define it.



Barrier Reef cross-section

Figure 1. Barrier reef cross-section. Reef separated from the shore by a relatively wide, deep lagoon.

Fringing reef cross-section

Figure 2. Fringing reef cross-section. Reef platform is continuous with the shore.

Atoll cross-section

Figure 3. Atoll cross-section. Reef surrounding a lagoon.

Shoreline Intertidal

Area between the mean high water line (or landward edge of emergent vegetation when present) and lowest spring tide level (excluding emergent segments of barrier reefs).

Typical Habitats:

Vertical Wall

Area with near-vertical slope from shore to shelf or shelf escarpment. This zone is typically narrow and may not be distinguishable in remotely sensed imagery, but is included because it is recognized as a biologically important feature.

Typical Habitats:

Lagoon

Shallow area (relative to the deeper water of the bank/shelf) between the shoreline intertidal zone and the back reef of a reef or a barrier island. This zone is protected from the high-energy waves commonly experienced on the bank/shelf and reef crest. If no reef crest is present there is no lagoon zone.

Typical Habitats:

Back Reef

Area between the seaward edge of a lagoon floor and the landward edge of a reef crest. This zone is present when a reef crest and lagoon exist.

Typical Habitats:

Reef Flat

Shallow (semi-exposed) area between the shoreline intertidal zone and the reef crest of a fringing reef. This zone is protected from the high-energy waves commonly experienced on the shelf and reef crest. Reef flat is typically not present if there is a lagoon zone.

Typical Habitats:

Reef Crest

The flattened, emergent (especially during low tides) or nearly emergent segment of a reef. This zone lies between the backreef and forereef zones. Breaking waves will often be visible in aerial images at the seaward edge of this zone.

Typical Habitats:

Forereef

Area from the seaward edge of the reef crest that slopes into deeper water to the landward edge of the bank/shelf platform. Features not forming an emergent reef crest but still having a seaward-facing slope that is significantly greater than the slope of the bank/shelf are also designated as forereef.

Typical Habitats:

Bank/Shelf

Deep water area (relative to the shallow water in a lagoon) extending offshore from the seaward edge of the fore reef to the beginning of the escarpment where the insular shelf drops off into deep, oceanic water. The bank/shelf is the flattened platform between the fore reef and deep open ocean waters or between the shoreline/intertidal zone and open ocean if no reef crest is present.

Typical Habitats:

Bank/Shelf Escarpment

The edge of the bank/shelf where depth increases rapidly into deep, oceanic water. This zone begins at approximately 20 to 30 meters depth, near the depth limit of features visible in satellite images. This zone extends well into depths exceeding those that can be seen on aerial photographs and is intended to capture the transition from the shelf to deep waters of the open ocean.

Typical Habitats:

Channel

Naturally occurring channels that often cut across several other zones.

Typical Habitats:
Dredged

Area in which natural geomorphology is disrupted or altered by excavation or dredging.

Typical Habitats:

Unknown

Zone, Cover, and Structure uninterpretable due to turbidity, cloud cover, water depth, or other interference.

Land

Terrestrial features above the spring high tide line.