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Island: Moloka‘i

Region: Moloka‘i

Watersheds: Kalama‘ula, Manawainui, Kāluape‘elua & Waiahewahewa

Figure 1: Map of watersheds in the Pālā‘au region (light green) of South Moloka‘i.
 

Geographic coordinates of watershed boundary:

South coast of Moloka‘i (21° 05‘N, 157° 06‘ W).

Watershed Area in Acres:

Perennial Streams:

none
 

Human Population:

2,265
 

Physiography:

An extremely broad reef flat and reef face is bisected by Pālā‘au Channel (Fig. 2 and 3). Much of the shallow reef flat is exposed at low tide. Sand, algae and silt dominate the reef flat with scattered coral colonies near the channel. Coral cover increases seaward of the reef flat to the reef crest and slope.

Extensive mangrove area occupies the shoreline, which has been advancing seaward for the past century due to high sediment loading. The mangroves and the floodplain intercept silt and consolidate sediments.

Figure 2: Aerial view of South Moloka‘i‘s Pālā‘au region.

Figure 3: Chart showing Pālā‘au coastline. Red arrows show location of CRAMP transect sites.
 

Reef Structure/Habitat Classification:

The general structure of the reef consists of an extremely broad reef flat and reef face bisected by Pālā‘au Channel. The reef flat near the inner channel and near the Fishing House is fully exposed at minus low tides. Sand and fine sediments cover most of the reef flat with no live coral. Moving seaward through the Pālā‘au Channel area takes one through a transition zone where small colonies of coral are found. There is a question as to whether these corals are remnants of a once-thriving area of healthy reef or if these corals will continue to decline with the progradation of the shoreline. If the mangroves have stabilized the mud flats, these corals may represent the beginnings of recovery in the area. As one moves seaward across the reef flat, crest and reef slope, more and more live healthy corals can be found. In the outer portion of the Pālā‘au Channel we find a healthy, diverse reef.

Figure 4: View of agricultural land upslope of Pālā‘au.  Turbid sediment plume over Pālā‘au reef can be seen in the distance.  Photo by Paul Jokiel.
 

Noteworthy Biota or Ecological Conditions:

The Inshore area is quite diverse. In the area of the CRAMP survey site one encounters two very rare corals: Gardinoseris planulata and Montipora studeri. The offshore site has extremely high coral cover.

The American Sugar Company introduced Rhizophora mangle, the Florida Red Mangrove to Pālā‘au in 1902 in an attempt to stabilize and contain the silt deposited near the shoreline. This introduced species quickly invaded the area extending its range seaward. A vast area of mud is now trapped behind this alien mangrove barrier. This invasive species has spread quickly invading coastal areas on the south shore of the island and has proliferated in and around many fishponds.

Oceanographic/Meteorological Conditions:

Although wave energy may be the dominant forcing function in determining coral community structure, light, temperature, salinity, nutrient and sediment regimes also play important roles.

Wave and Current Regime:

Optimum reef growth is usually observed between 10 and 20 meters. Coral growth appears to be a trade-off between wave energy and available light. Thus, less developed reefs in high wave environments have lower coral cover and a species composition that reflects the wave regime, while reefs with low wave energy regimes are well-developed and support high coral cover and more delicate, branching species. This is evident from Pālā‘au westward.

The wave wrap around from the west side begins to diminish at Pālā‘au. The lack of high wave activity is responsible for the high coral cover and dominance of Porites compressa and Montipora capitata with its branching morphology conducive to lower water motion regimes (Storlazzi et al., 2001).

Westward of Pālā‘au the coral cover and composition change rapidly in response to changes in the wave regime. Within 8 km of the west end of the island, the cover of the branching species, Porites compressa drops rapidly, while the plate morphology of Montipora capitata increases. As wave energy increases moving westward, Porites lobata, a species more tolerant of high wave energy due to its lobate or encrusting morphology, increases from less than 5% to over 30% then decreases thereafter. Pocillopora meandrina, another extremely wave tolerant species due to morphology and high skeletal strength, also increases near the west end (Storlazzi et al., 2001).

Human Use Patterns:

As in the past, current use of the reef resources in the Pālā‘au area is largely focused on subsistence fishing.

The terrestrial environment has been severely altered over time. Geologic evidence determined two shield volcanoes formed the island of Moloka‘i approximately 2 million years ago (Fig. 5). The Ho‘olehua saddle which lies between these two volcanoes is rich in alluvial plains deposits from millions of years of erosion from Moloka‘i’s two founding volcanoes.

Figure 5: Elements affecting reef deposits from the Pālā‘au watershed

With the arrival of Westerners came accelerated erosional loss of nutrient-rich topsoil. In the period following western contact high rates of sedimentation and reef deposition occurred.

In the mid 1800’s, much of the upper saddle was used for cattle ranching. Problems associated with both grazing and soil compaction from trampling by herds driven to docks at Pālā‘au for shipment to O‘ahu. Sediment deposition in the lowland plains reached an alarming rate of one foot per 6 years. The progadation rate of sediment from 1886 to 1983 has been extensive (Fig. 6).

Figure 6: Progradation of shoreline on the south central coast of Moloka’i. From Roberts 2001.

This devegetation of the saddle region by cattle was accelerated by sheep ranching in the early 1900’s that denuded pasture lands. Due to this reduction in pasture land combined with a depressed market for wool, sheep rearing was discontinued.
The environmental damage caused by feral animals including wild cattle, goats, sheep and deer were accelerated by a decline in human population in the surrounding area. Population estimates at the time of initial European contact was approximately 10,000 found mainly on the more hospitable southeastern coast. By 1840 the population had dropped by half and by the turn of the century the population had shifted towards the west and declined to less than 2,500. As a direct result of this population decline, the feral animal populations increased from lack of predation (Summers 1971).

The denuded landscape, reduced water supply and declining population led to loss of farmed lands.

Hawaiian Homestead Lands in the Ho‘olehua Saddle were established in 1920. Due to degraded soils few homesteaders farmed their own lands. Pineapple plantations leased lands from owners further accelerating the environmental damage. Large plantations requiring little water and continued cattle grazing increased sedimentation onto the coastal plains and adjacent reef flat. Most fishponds in this area were unusable due to substantial sediment deposits that filled the ponds (Handy 1931).

Agricultural experimentation in the first half of the 19th century introduced insect pests and disease. Ho’olehua Homestead was not developed further due to lack of water and drought.

To assist homesteaders in restoration efforts, the Dept. of Agriculture formed the Moloka‘i-Lāna‘i Soil Conservation District. Promotion of conservation efforts through assistance and dissemination of information had limited success due to lack of continued funding.

In 1983, the Nature Conservancy continued the attempt to reverse the damage to the environment and halt its progression. State and federal agencies are currently working with local hunters in an attempt to control feral animal populations (Kepler and Kepler, 1991).

The USGS is working with the community and university programs to address the sedimentation problems to the coastal reef environment.

Economic Value and Social Benefits:

Subsistence fishing is commonly practiced on the south shore of Moloka‘i. With increased fishing pressure, stocks have steadily declined. Once practiced regularly in the Kamalō region, drag netting and bull pen fishing moved to the Kawela and Pālā‘au areas as a result of community pressure at Kamalō (Baker, 1987).

Status (Degree of Legal Protection):

Open access, no special protection. 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).

Management Concerns:

Over the past century the management concern at Pālā‘au is severe sedimentation due to accelerated land erosion.

Historical and Cultural Importance:

Hawaiian fishponds integrated fish ecology with geology, hydrology and engineering. These archeological structures can be found nowhere else in the world. Ten fishponds can be found within the Pālā‘au watershed. Three ponds are located in Nāiwa, four in Kalama‘ula and one in īloli. The ponds at Pālā‘au and Ho‘olehua are extensive ponds that have been filled with mud (Fig. 7). A small inland pond at Kalama‘ula is less than one acre in size.

The Pālā‘au Fish House is located on the reef flat on the east side of the channel. The fish house which is frequented by overnight fishermen is most easily accessible by boat. It can also be accessed from Moloka‘i Sea Farms across a path cut through the mangroves and over the shallow reef flat.

Figure 7: Pālā‘au mudflats and surrounding mangroves. Photo by Kurt Storlazzi.

Scientific Importance and Research Potential:

This site was chosen as one of the Coral Reef Assessment and Monitoring Program (CRAMP) sites for the Project. Biological transects are laid out at 3m and 10m depths, and an additional CRAMP photoquadrat area is on the reef flat in 1 m of water. Site selection was based upon the premise that Pālā‘au was the western end point before high wave energy from the wrap around effect changed the morphology and composition of the reef. The photoquad site on the inner reef flat along the west edge of the channel is a transitional zone where mainly small colonies of coral are found. It is unknown at this point as to whether these corals are remaining from a more expansive reef or are newly recruited to this area. CRAMP baseline data was collected in February 2000. The location is revisited annually to detect change.

The USGS has deployed time series sediment traps and a wave gauge at 10 meters in the area. The focal points of scientific investigations at this location center on the impact of sedimentation (increasing damage or recovery) and the importance of wave energy in structuring the coral reef communities. The inshore mangrove area is also the subject of ongoing studies.

References

Baker, Michael E.1987.Backyard fishing on the south coast of Moloka‘i. MA Thesis, University of Hawai‘i at Mānoa, Honolulu, 128 pp

Handy, E.C. 1931. Cultural Revolution in Hawai‘i. Paper presented to the Fourth General Session of the Institute of Pacific Relations. Hangchow, China.

Kepler, A.K. and C.P. Kepler. 1991. Majestic Moloka‘i: A nature lovers guide. Honolulu, Mutual Publishing.

Roberts, Lucile. 2000. Historical Land Use, Coastal Change, and Sedimentation on South Moloka’i Reefs. Recent Advances in Marine Science and Technology, 2000 PACON International 2001 Honolulu, Hawai‘i.

Storlazzi, C.D., Field, M.E., Dykes, J.D. Jokiel, P.L., Brown, E.K. 2001. Wave control on reef morphology and coral distribution: Moloka‘i, Hawai‘i. Ocean Wave Measurement and Analysis. Proceedings of the Fourth International Symposium Waves 2001, American Society of Civil Engineers. San Francisco, California.

Summers, C.C. 1971. Moloka‘i: A Site Survey. Pacific Anthropological Records, No. 14, Honolulu, Bishop Museum.

Last Update: 04/21/2008

By: Lea Hollingsworth

Hawai‘i Coral Reef Assessment & Monitoring Program

Hawai‘i Institute of Marine Biology

P.O. Box 1346

Kāne‘ohe, HI 96744

808-236-7440 phone

808-236-7443 fax

email: jokiel@hawaii.edu