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Pacific Coastal and Marine Science Center

USGS Pacific Coral Reefs

Photo of coral reef.  

Project Videos

“Breaking Down Reefs, Building Up Beaches”

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“Exploring Causes of Coral Disease”

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Videos of the South Molokaʻi Reef Tract

Coral reef near Kamalō
The South Molokaʻi reef tract near Kamalō Harbor forms a complex pattern of channels, blue holes, and shallow reef flat. Kamalō also lies offshore from the most mountainous part of Molokaʻi, which receives the highest annual precipitation. The living reef in this video is close to shore in very shallow water and generally very healthy, however high sediment loads from streams or construction activities are a nearby threat. Broken and dead colonies of coral attest to the impact of large waves, which occasionally wash across the reef flat to this shallow area.

Coral reef offshore from Kapuāiwa (King Kamehameha V) coconut grove
Outer fore reef corals, at 25-40 feet depth (7-12 m), offshore from the Kapuāiwa coconut grove (near Kaunakakai), are representative of the generally very healthy reefs of the south coast of Molokaʻi. Species diversity is relatively high. The water is clear, and sediment that is present in the system is largely derived from the natural breakdown of the reef. During scuba dives, scientists collect samples from coral-encrusted pavements and spur-and-groove channels to detect the amount of sediment that comes from land sources. This footage was taken approximately one mile west of the Kaunakakai Wharf and shows us that reef health is locally variable.

Coral reef near Pālāʻau
Near Pālāʻau, the shallow coral reef flat reaches its widest development on southern Molokaʻi, approximately 1.5 miles (2.5 km). At the time this video was taken, a recreational fishing structure (known locally as the Fish Hut) is built on the reef flat at the edge of a channel. Viewed from the air, the channel cuts across the reef flat. The channel likely originates from a recent period of lower sea lever when streams flowed directly across the reef flat. At present, it focuses land-derived sediments that have funneled between the volcanic highlands of west and east Molokaʻi. Sediment is transported across the reef, suspended in water, possibly affecting coral reef health, as evidenced by the general lack of living coral in this nearshore area. A fishing net caught on a coral reef head is evidence of human impact on the reef. Coral rubble, debris from coralline algae, and mud and sand from land blanket the shoreward stretches of the reef. For a reef that is noted for its overall excellent health, portions clearly are degraded by both human-induced and natural processes.


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Page Last Modified: 13 April 2016 (lzt)