CRAMP Study Sites: Olowalu, Island of Maui
Geographic Name: Olowalu
CRAMP Site Code: MaOlo
20° 48.505‘ N; 156° 36.693‘ W
20° 48.363‘ N; 156° 36.733‘ W
Chart showing Olowalu coastline. Red arrows show location of transect sites. (Click image for larger view.)
1993 NOAA aerial photo of the Olowalu area. Image provided by Steve Rohmann. (Click image for larger view.)
Olowalu is located on the eroded west flank of the volcano that originally formed west Maui. Inland, the terrain is mountainous forest reserve. The watershed consists of the large Olowalu valley which has steep walls and is drained by Olowalu stream. The lower areas of the valley have a more moderate slope and were in sugar cane production until recently. A narrow coastal plain is occupied by the main road connecting West Maui with the rest of the island. A narrow basalt rampart separates the narrow olivine sand beach and the adjacent highway. Sections of the shoreline adjacent to the road are undergoing erosion. The subtidal consists of basalt cobble. A reef platform extends seaward with extensive sand channels interspersed with large aggregated coral formations. These large structures may be tahe result of reef accretion or may be volcanic covered with a veneer of limestone. Offshore topography is quite varied and complex with high relief.
Reef Structure, Habitat Classification:
The Olowalu site contains some of the most extensive "spur and groove" reef formations seen on Maui. Coral cover is moderate to high (30-40%) in deeper water with substantial relief above the sand channels. Sand in the area is a mixture of carbonate (Halimeda fragments) and terrigenous sediments (high olivine content). At 4 m depth large heads of the coral Porites lobata are found. Numerous dead coral heads are found throughout the area and appear to be killed by resuspended sediments during high wave conditions. Live colonies also abound. The carbonate substrata and dead corals have an unusual dark appearance due to a thin coating of fine black basaltic sediment. The area is characterized by high coral diversity, moderate coral cover, complex bottom relief with varied reef formations. Coral coverage increases seaward.
These leeward reefs are well protected from all but the most severe south swells. The very gradual slope dissipates wave energy over the width of the reef (up to 1 mile offshore in some places). High turbidity develops during periods of south swell due to the resuspension of benthic sediments.
Adjacent Land Tenure, Land Use:
The steep mountainous valley of Olowalu is in forest reserve (West Maui Natural Reserve Area and West Maui Forest Reserve. The lower portion of the Olowalu watershed was formerly used for sugar cane production. The fields have been taken out of production with the closing of the mills, and recently have been lying follow (2000). These may go into diversified agriculture, but areas at the north end of Olowalu are already under consideration for housing development.
Human Use Patterns:
Olowalu can be easily reached from the road. Consequently, this is a popular site for tourists and residents alike. The site is also accessible by boat. Parking is limited and there are no public facilities, so the area is only lightly used for recreational skin diving. Creel surveys during June and July of 1987 showed light fishing activity (Ambrose et al., 1988).
Economic Value and Social Benefits:
This is a popular area for skin diving and limited subsistence fishing.
Status (Degree of Legal Protection):
Open access - no special marine life conservation restrictions. Authority for managing the marine resources within three miles (4.8 km) of the high tide mark lies with the Division of Aquatic Resources, Department of Land and Natural Resources. All laws pertaining to the management of state marine resources apply (see pamphlet "Hawai‘i Fishing regulations, September 1999", 51 pp. available from Division of Aquatic Resources, Department of Land and Natural Resources, Kalanimoku Building, 1151 Punchbowl St., Rm. 330, Honolulu, Hawai‘i).
A section of shoreline adjacent to the road is undergoing erosion and has been fortified with large basalt boulders. Photo by Paul Jokiel. (Click image for larger view.)
Past concerns were over impact of agricultural practices that can lead to increased sedimentation. At present there is growing concern about possible urbanization of the area in future years. The shoreline off Olowalu is subject to coastal erosion, a factor that contributes to reef decline.
Noteworthy Flora and Fauna:
This area has a highly diverse coral fauna. Coverage is only moderate, but many uncommon coral species are found here.
Scientific Importance and Research Potential:
This site has been well studied by a variety of agencies which include the Pacific Whale Foundation, Western Washington University, University of Hawai‘i, and the State of Hawai‘i Department of Land and Natural Resources (DLNR).
An unusual feature off Olowalu is the presence of dark basaltic sand mixed with dead Halimeda fragments. These fragments are the dead remains of a calcareous frondose algae and have the appearance of corn flakes. Live Halimeda cannot be found inshore, but occurs offshore at depths of 60 feet and is apparently transported inshore by waves and currents. Photo by Paul Jokiel. (Click image for larger view.)
Dead coral skeletons at Olowalu take on an unusually dark color due to the presence of fine basaltic sand. The dark color of these dead skeletons contrasts with the Halimeda fragments. the large number of dead colonies suggests frequent disturbance by sedimentation events, sand burial and/or algal blooms due to nutrient pulses. Photo by Paul Jokiel. (Click image for larger view.)
Algae turf at Olowalu competes with the reef corals for space. The abundance of algae here suggests that nutrients may be reaching the reef through seepage from ground water and runoff. High nutrient levels can favor the development of algae to the detriment of corals. Septic systems and runoff from any future development or increased use of fertilizers for agricultural purposes could exacerbate the problem. Photo by Paul Jokiel. (Click image for larger view.)
Last Update: 02/24/2011
By: Dan Lager
Hawai‘i Coral Reef Assessment & Monitoring Program
Hawai‘i Institute of Marine Biology
P.O. Box 1346
Kāne‘ohe, HI 96744