Wai‘anae Ecological Characterization

Coral Reefs

The value of Hawai‘i's coral reefs cannot be overstated. They provide shoreline protection from waves and storm surge. They have provided a continuous supply of fresh fish and other basic food for the people of Hawai‘i for the past thousand years. They are the source of the sand on Hawai‘i's beaches. They are an integral aspect of Hawai‘i's multi-billion dollar tourist industry, providing countless snorkeling, diving, surfing, and fishing opportunities. A recent analysis estimated that Hawai‘i's coastal reefs generate $364 million annually in added value, with 84 percent of this money coming from snorkeling and diving activities (Cesar 2003). Coral reefs and hard bottom habitats are found along the length of the Wai‘anae coast and provide food and shelter for reef fish and invertebrates (see map).

Reef Structure

Most reefs on the inhabited islands of Hawai‘i are known as fringing reefs, growing near the shoreline. Fringing reefs are the first type of reef to form around young volcanic islands, such as Hawai‘i, Maui, O‘ahu, and Kaua‘i. These reefs form in areas of low rainfall runoff, primarily along the leeward shores such as the Wai‘anae coast of O‘ahu. Typical reef zonation consists of (1) reef flat zone (0 to 2 meters or 0 to 6.5 feet), (2) reef bench zone (2 to 10 meters or 6.5 to 32.8 feet), (3) reef slope zone (10 to 30 meters or 32.8 to 98.4 feet) and (4) rubble zone (30 to 40 meters or 98.4 to 131 feet) (AECOS, Inc. 2002).

Reef Flat Zone. Off the Wai‘anae coast, sand is affected by substantial wave energy, especially through the winter due to the wrap-around effect from North Pacific storms. Below the waterline, sand does not continue; instead, there is a limestone platform, or reef flat, that extends several meters offshore. This platform is virtually barren of macroinvertebrates and macroalgae, although covered with short turf algae. Corals, represented by the compact and sturdy cauliflower coral (Pocillopora meandrina), are distributed in patches on the reef flat. Animals living in this zone need to contend with strong surge and crashing waves by either boring into the rock (urchins), or by darting out between waves from a protective hole to feed on turf algae (AECOS, Inc. 2002).

Reef Bench Zone. The limestone platform drops off vertically within 10 to 20 meters (approximately 30 to 65 feet) from shore, and the deeper vertical portions, known as the reef bench, contain the corals P. meandrina, Porites lobata, and Lepastrea purpurea. In areas of boulders, the common brown algae (Padina spp.) and red algae (Liagora spp.) are present. Unattached benthic invertebrates, such as sea urchins, are rare. Reef fish are moderately abundant around the boulders, and in the deeper areas of the shoreline bench (AECOS, Inc. 2002).

Reef Slope Zone. Wave energy subsides at the depth of the reef slope zone, and the more delicate finger coral becomes common. The greatest concentration of living material is here, at the reef's seaward edge, where plankton and clear water of normal salinity are dependably available. The characteristics of the seafloor are of great importance in structuring fish communities and in determining the number of fishes living in the area. In areas of high relief, where fish can seek refuge, a high abundance and diversity of fishes are present. Large schools of taape (bluelined snapper; Lutjanus kasmira), kole (goldring surgeonfish; Ctenochaetus strigosus), aloiloi (black damselfish; Dascyllus albisella), and other common fish species are present swimming over these rocks (Russo 1997). Sandy bottoms or pavement rock generally attract very few fish to the area (AECOS, Inc. 2002).

Rubble Zone. Coral cover diminishes in the rubble zone, and coral rubble and sand dominate the seascape. Fish concentrations drop off considerably, as the habitat provides little refuge in this zone (AECOS, Inc. 2002).

Coral Species and Cover

Coastal sites with high wave exposure have the lowest coral cover (less than 10 percent), while bays and wave-protected coastal areas have the highest coral cover (70 to 80 percent) (Brainard and others 2002). Coral cover is low along the Wai‘anae coast (one to two percent of bottom area), a condition typical of shallow, flat, low-relief bottoms in this area (Russo 1997). A 20-year monitoring study of high surf and hurricane impacts on the Wai‘anae coast determined that while hurricanes have a significant impact on the coral reef environment (namely, the reduction of coral cover), impacts from high surf and storm surge are much less predictable (Coles and Brown in press). Most of the seafloor is uncolonized pavement, a flat hardbottom of volcanic or limestone rock, interspersed with sand channels. However, corals thrive on the artificial reefs and on the armor rock at the inshore wastewater effluent pipeline, probably because of artificial topographical relief (Harrison 1987).

The Wai‘anae moku is dominated by two coral species, P. meandrina and P. lobata (Russo 1997). P. lobata, a massive and encrusting species, is the most common coral in the main Hawaiian Islands. It is surge-tolerant and can be found in a variety of habitats, from tide pools to depths of 45 meters (approximately 145 feet). It is most common on wave-exposed reef slopes between three and 14 meters (approximately 10 to 45 feet), in a zone below the cauliflower coral. P. meandrina is one of the four most abundant species of Hawaiian reef-building corals. It is a surge-tolerant species that inhabits exposed shorelines and the surge zone of reef slopes. Its dense skeleton, sturdy branches, and symmetrical head formation suit it to the moderate wave action encountered close to the surface. It is the dominant coral species on reef slopes at depths of less than three meters (10 feet), but can also be found to 27 meters or more (greater than 85 feet in depth). The thin encrusting species L. purpurea is also found in Wai‘anae.

Fish and Other Species

There are 557 documented species of reef and shore fish in Hawai‘i, of which 135 are endemic. Surgeonfish are the dominant fish group, and herbivores generally account for over 70 percent of the total reef fish biomass, followed by invertebrate feeders (13 percent) and plankton feeders (9.7 percent). Predators are rare, accounting for 3.8 percent of reef fish biomass (Brainard and others 2002).

The highest numbers and species of fish are found in locations of moderate wave exposure. The lowest biomass is found in areas exposed to north and south swells. Increasingly complex habitats have more fish and a greater variety of species, which illustrates the importance of shelter as a refuge for some fish to avoid predation (Jokiel and others 2001). Exceptions do occur in a few places around the islands where high fish biomass occurs in sites with low habitat complexity, but these sites are protected from fishing. The Wai‘anae coast has few locations with complex habitat and has no no-fishing areas. Thus, most of the reef along the coast has low species diversity and biomass.

Although the Wai‘anae coast in general offers relatively few fish species and low numbers of fish, there are exceptions where large schools of reef fish have been documented. They include the three artificial reefs: Pōka‘ī Bay Artificial Shoal (created with old cars, concrete pipes and a steel barge in 1963), the Mahi shipwreck (sunk in 1982) and the seaplane wreck (sunk in 1986), the outfall pipe of the wastewater treatment plant in Wai‘anae town; and the thermal outfall of the Kahe power plant just south of the Wai‘anae moku (Kanenaka 1991; Russo 2001a, b; Harrison 1987).

The weke (yellowstripe goatfish; Mulloidichthys flavolineatus), na‘ena‘e (surgeonfish; Acanthurus dussumieri), u u (menpachi; Myripristis berndti), and the saddleback wrasse (Thalassoma duperrey) occur in large schools at these sites (Hobson 1984). Also common are the brown surgeonfish (Acanthurus nigrofuscus), Pacific Gregory (Stegastes fasciolatus), goldring surgeonfish (Ctenochaetus strigosus) and the blackfin chromis (Chromis vanderbilti). Armor rock surrounding pipes and artificial reefs provide ample habitat space for hiding and mating, ample surface for the colonization of food sources, and a reference point above the seafloor for aggregation and maintenance of schools. Artificial structures placed in areas normally devoid of bottom relief can attract large numbers of fish and provide surfaces for coral and other sessile organism attachment. For more information about fish and artificial reefs, please see the Coastal and Marine Resource Use: Fishing section.

Macroalgae represent over 50 percent of the benthic cover in the Hawaiian coral reef ecosystem. Red algae are the most commonly occurring algae in Hawai‘i, representing four of the five most common species. Green and brown algal species are found in most reefs in smaller numbers (Brainard and others 2002).

Research and Monitoring

The Kahe power plant outfall, just south of the Wai‘anae moku, is the longest running coral reef study area in the world, with monitoring occurring continuously since 1971 (AECOS, Inc. 2003). The rocks around the twin thermal outflow pipes form an artificial reef. Surveys of coral cover, fish species richness and biomass, sand movement, and water quality are prepared for the Hawaiian Electric Company annually. A number of more extensive surveys of marine life, including detailed studies of phytoplankton to marine mammal assemblages, have occurred sporadically at this site.

The Wai‘anae Wastewater Treatment Plant (WWTP) outfall pipeline was installed in 1986 and extends 1.8 kilometers offshore into 33 meters of water. Benthic community structure and fish community structure have been monitored quantitatively at sampling stations every year since 1990 for possible effects of treated sewage effluent inshore of the outfall diffuser discharge (Russo 2001a, b). Current year data are compared with data from previous years to determine whether any statistically significant change has occurred in the measured biological parameters. In 1996, the WWTP was converted from a primary to a secondary WWTP, reducing the concentration of the effluent entering the ocean. A noticeable decline in fish abundance around the diffuser in subsequent years was attributed to this conversion.

The state's artificial reef program has monitored numbers of fish, estimated total biomass, and species richness or diversity at the major sites along the Wai‘anae coast. Regular surveys have been conducted at the Pōka‘ī Bay Artificial Shoal since 1962, and fish abundance has been monitored at the sunken vessel Mahi since 1986 (Kanenaka 1991).

The Hawai‘i Coral Reef Assessment and Monitoring Program was created during 1997-1998 by leading coral reef researchers, managers, and educators in Hawai‘i. The program developed a statewide network of over 30 long-term coral reef monitoring sites, with three on the Wai‘anae coast. All of them are in the vicinity of the Kahe power plant, to build on the 30-year data set from that location. Rapid quantitative assessments of the benthic and fish species were conducted and compared among sites. The three Kahe sites were among the least abundant and diverse across the islands. These data will be used in conjunction with the National Oceanic and Atmospheric Administration's shallow water habitat maps to understand their ecology in relation to other geographic areas.

References Cited

AECOS, Inc. 2003. Annual Report: Kahe Generating Station. AECOS No. 649M. NPDES Monitoring Program. Hawaiian Electric Co., Inc. 49 pp.

AECOS, Inc. 2002. Inventory Catalogue of Hawaii's Coral Reefs. Hawaii Wildlife Fund. http://home.hawaii.rr.com/cpie/CoralReefBib.html

Brainard, R., D. Gulko, C. Hunter, A. Friedlander, R. Kelty and J. Maragos. 2002. Status of Coral Reefs in the Hawaiian Archipelago. In Status of Coral Reefs of the World. 14 pp.

Cesar, H. 2003. Economic Valuation of Coral Reefs in Hawaii. Hawaii Coral Reef Initiative Program, 2001-2003. Report of Hawaii Coral Reef Initiative Program. http://www.hawaii.edu/ssri/hcri/rp/reports_by_principal_investigator-cesar.htm

Coles, S.L., and E. Brown. in press. Twenty-Year Changes In Coral Coverage On a Hurricane Impacted Reef in the Vicinity of a Thermal Outfall.

Harrison, J.T. 1987. 40 MW(e) OTEC Plant at Kahe Point, Oahu, Hawaii: A Case Study of Potential Biological Impacts. NOAA-TM-NMFS-SWFC-68. National Oceanic and Atmospheric Administration. 105 pp.

Hobson, E.S. 1984. "Structure of Reef Fish Communities in the Hawaiian Archipelago." Proceedings of the Second Symposium on Resource Investigations in the Northwestern Hawaiian Islands. Honolulu, HI. University of Hawaii Sea Grant College Program, UNIHI-SEAGRANT-MR-84-01. p. 101-122.

Jokiel, P., E.K. Brown, A. Friedlander, S.K. Rodgers, and W.R. Smith. 2001. Hawaii Coral Reef Initiative: Coral Reef Assessment and Monitoring Program (CRAMP) Final Report, 1999-2000. Prepared for Hawai`i Coral Reef Initiative, University of Hawaii, and NOAA National Ocean Service. http://cramp.wcc.hawaii.edu/Results/Final_Reports/Final_Report_1999-2000.pdf

Kanenaka, B.K. 1991. "Hawaii's Artificial Reef Program: Past, Present and Future." Proceedings of the Fifth International Conference on Aquatic Habitat Enhancement. Long Beach, CA.

Russo, A.R. 1997. Survey of Selected Coral and Fish Assemblages Near the Waianae Ocean Outfall, Oahu, Hawaii (1996). Project Report PR-97-03. Water Resource Research Center.

Russo, A.R. 2001a. Benthic Sampling Adjacent to the Waianae Ocean Outfall, Oahu, Hawaii (June 2000). Project Report PR-2001-04. Water Resource Research Center.

Russo, A.R. 2001b. Survey of Selected Coral and Fish Assemblages Near the Waianae Ocean Outfall, Oahu, Hawaii (2000). Project Report PR-2001-06. Water Resources Research Center.

Related References

Ball, E.E., D.C. Hayward, J.S. Reece-Hoyes, N.R. Hislop, G. Samuel, R. Saint, P.L. Harrison, and D.J. Miller. 2002. "Coral Development: from Classical Embryology to Molecular Control." International Journal of Developmental Biology 46(4): 671-678.

Brock, J.A. 1998. Necropsy and Liver Histopathology for Fish Sampled in the Vicinity of the Waianae Ocean Outfall, Oahu, Hawaii, September - October, 1997. Project Report PR-2000-09. Water Resources Research Center.

Brock, J.A. 1999. Necropsy and Liver Histopathology for Fish Sampled in the Vicinity of the Waianae Ocean Outfall, Hawaii. June 1998. Project Report PR-99-03. Water Resource Research Center.

Brock, J.A. 2000. Necropsy and Liver Histopathology for Fish Sampled in the Vicinity of the Waianae Ocean Outfall and at the Reference Station in Maunalua Bay, Oahu, Hawaii. Project Report PR-2000-09. Water Resources Research Center.

Coles, S.L. 1979. Annual Report. Kahe Generating Station. NPDES Monitoring Program. Hawaiian Electric Co., Inc. 263 pp.

Coles, S.L. 1980. Annual Report. Kahe Generating Station. NPDES Monitoring Program. Hawaiian Electric Co., Inc. 277 pp.

Coles, S.L., and D.T. Fukuda. 1975. Reef Coral and Algal Communities of the Kahe Nearshore Region of Oahu, Hawaii. Environmental Department. Hawaiian Electric Co., Inc. 89 pp.

Coles, S.L., and D.T. Fukuda. 1984. Annual Report. Kahe Generating Station. NPDES Monitoring Program. Hawaiian Electric Co., Inc. 225 pp.

Coles, S.L., and D.T. Fukuda. 1983. Annual Report. Kahe Generating Station. NPDES Monitoring Program. Hawaiian Electric Co., Inc. 173 pp.

Coles, S.L., and J.C. McCain. 1973. Effects of the Kahe Generating Station on the Nearshore Environment. A Report of the 1973 Monitoring Program. Hawaiian Electric Co., Inc. 199 pp.

Coles, S.L., D.T. Fukuda, and C.R. Lewis. 1982. Annual Report. Kahe Generating Station. NPDES Monitoring Program. Hawaiian Electric Co., Inc. 221 pp.

Coles, S.L., D.T. Fukuda, and C.R. Lewis. 1981. Annual Report. Kahe Generating Station. NPDES Monitoring Program. Hawaiian Electric Co., Inc. 237 pp.

Coles, S.L., D.T. Fukuda, and K.S. Oda. 1985. Annual Report. Kahe Generating Station. NPDES Monitoring Program. Hawaiian Electric Co., Inc. 172 pp.

Coles, S.L., K.S. Oda, and J.M. Peck. 1986. Annual Report. Kahe Generating Station. NPDES Monitoring Program. Hawaiian Electric Co. 109 pp.

Davidson, K., M. Hamnett, and C. Minato (eds). 2003. First Four Years: Hawaii Coral Reef Initiative Research Program, 1998-2002. Social Science Research Institute, University of Hawaii at Manoa. 72 pp. http://www.hawaii.edu/ssri/hcri/files/summary_report.pdf

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Dollar, S.J., and R.W. Grigg. 2004. "Anthropogenic and natural stresses on selected coral reefs in Hawaii: A multi-decade synthesis of impact and recovery." Pacific Science 58(2): 281-304.

Douglas, A.E. 2003. "Coral Bleaching - How and Why?" Marine Pollution Bulletin 46: 385-392. http://fig.cox.miami.edu/~ddiresta/BIL151/Bleaching.pdf

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Jokiel, P., E.K. Brown, A. Friedlander, S.K. Rodgers, and W.R. Smith. 2003. "Hawaii Coral Reef Assessment and Monitoring Program: Spatial patterns and temporal dynamics in reef coral communities." Pacific Science58(2): 159-174.

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Russo, A.R. 1993. Survey of Selected Coral and Fish Assemblages Near the Waianae Ocean Outfall, Oahu, Hawaii (1993). Project Report PR-94-10. Water Resources Research Center.

Russo, A.R. 1995. Survey of Selected Coral and Fish Assemblages Near the Waianae Ocean Outfall, Oahu, Hawaii (1994). Project Report PR-95-04. Water Resources Research Center.

Russo, A.R. 1996. Survey of Selected Coral and Fish Assemblages Near the Waianae Ocean Outfall, Oahu, Hawaii (1995). Project Report PR-96-01. Water Resource Research Center.

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Russo, A.R., E.A. Kay, J.H. Bailey-Brock, and W.J. Cooke. 1999. Benthic Sampling Adjacent to the Waianae Ocean Outfall, Oahu, Hawaii (May 1998). Project Report PR-99-06. Water Resources Research Center.

Russo, A.R., E.A. Kay, J.H. Bailey-Brock, and W.J. Cooke. 1998a. Benthic Sampling Adjacent to the Waianae Ocean Outfall, Oahu, Hawaii (October 1996). Project Report 98-02. Water Resource Research Center.

Russo, A.R., E.A. Kay, J.H. Bailey-Brock, and W.J. Cooke. 1998b. Benthic Sampling Adjacent to the Waianae Ocean Outfall, Oahu, Hawaii (July 1997). Project Report PR-98-11. Water Resource Research Center.

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