Prepared for

Two transects (numbers 5 and 6) were established on limestone substratum offshore of the Honolulu International Airport Reef Runway. This station lies between 760 and 840 m seaward of the runway in water ranging from 9.1 to 11.6 m deep. The substratum of this area is a mosaic of emergent limestone spur and groove formations grading seaward into a series of low limestone mounds. The general orientation of the spur and groove formations is perpendicular to the shoreline and direction of usual wave impact. The spurs are from 5 to 40 m in width, 30 to 80 m in length and are spaced from 10 to 100 m apart. Sand is the dominant substratum in the intervening areas. The maximum topographical relief formed by these spurs is about 3.5 m. Just seaward of the spurs and grooves is a zone of low emergent limestone; these “patches” of hard bottom are from 5 ¥ 10 m to several hundred square meters in size; spacing of these limestone areas is between 10 to 50 m and sand is again found in the interven-ing areas. Corals are restricted to the areas of hard substratum. Water clarity at this station ranged from 7 to 20 m during our 1992 visits; usually the clarity did not exceed 12 m. Hurricane Iniki caused considerable damage to the benthic communities at Station C. A large (approximately 60 m in diameter) sand patch located between Transects 5 and 6 has disappeared and has been replaced by coral rubble. Much of the hard substratum on both transects was broken and the underlying limestone rock exposed and crevices and holes were filled with coral rubble. The result of this has been a change in the abundance of both invertebrates and fishes at this location.

Both transects were established on spurs or ridges of limestone (see Fig. 4). Transect 5 was established on a limestone ridge at a depth of 9.1 to 11 m. Table 6 presents the results of the biological survey carried out at Station 5. The quadrat survey noted the coralline algal species (Porolithon onkodes), two soft corals (Anthelia edmondsoni and Palythoa tuberculosa), and four coral species (Porites lobata, P. compressa, Pocillopora meandrina, and Pavona duerdeni) having a mean coverage of 0.4 percent. This coverage is down from the previous survey (2.1%). The invertebrate census found one hermit crab (Calcinus herbstii) and two sea urchin species, the green sea urchin (Echinometra mathaei) and the black sea urchin (Tripneustes gratilla). The photographic quadrat survey completed after Hurricane Iniki noted the encrusting coralline algae (Porolithon onkodes), soft coral (Palythoa tuberculosa), and two coral species (Porites lobata and Pocillopora meandrina) having a mean estimated coverage of 0.2 percent (down 2% from the previous year).

The fish census (App. Table A) counted 136 individuals amongst 23 species. The most common species included the manybar goatfish or moano (Parupeneus multifasciatus), the brown surgeonfish or ma‘i‘i‘i (Acanthurus nigrofuscus), and the goldring surgeonfish or kole (Ctenochaetus strigosus). The standing crop of fishes on Transect 5 was estimated to be

Transect 6 was established approximately 80 m seaward of Transect 5. The substratum at Transect 6 was similar to Transect 5 and is situated on a limestone spur that is about 40 m wide and 80 m long. Water depth at this site varies between 10.7 to 11.6 m. A summary of the biological observations made on Transect 6 is given in Table 7. The quadrat survey found two algal species (Porolithon onkodes and Cladymenia pacifica having a mean coverage of 6.5%), one soft coral (Anthelia edmondsoni), and six coral species (Porites lobata, P. compressa, Pocillopora meandrina, Montipora patula, M. verrucosa, and Pavona duerdeni) having a mean coverage of 3.1 percent. This coral coverage estimate is down 3.6 percent from last year’s survey. The census of macroinvertebrates noted three species: the terebellid polychaete worm (Loimia medusa), the green sea urchin (Echinometra mathaei), and the black sea urchin (Tripneustes gratilla). The photo quadrat survey noted coralline algae (Porolithon onkodes) with a mean coverage of 15 percent as well as three coral species (Porites compressa, P. lobata, and Pocillopora meandrina) with a mean coverage of 5 percent.

The fish census found 247 individuals belonging to 36 species in the 4 ¥ 20 m census area. The most abundant fishes on Transect 6 included the damselfish (Chromis vanderbilti), the brown surgeonfish or ma‘i‘i‘i (Acanthurus nigrofuscus), the goldring surgeonfish or kole (Ctenochaetus strigosus), and the plankton feeding surgeonfish (Acanthurus thompsoni). The standing crop of fishes on this transect was estimated to be 108 g/m²; the largest contributors to this biomass included the bullethead parrotfish or uhu (Scarus sordidus - 22% of the total), the goldring surgeonfish or kole (Ctenochaetus strigosus - 17%), the black triggerfish or humuhumu ‘ele‘ele (Melichthys niger - 11%), and the brown surgeonfish or ma‘i‘i‘i (Acanthurus nigrofuscus - 8%).

There were from one to three green sea turtles (Chelonia mydas) usually present at Transect 6 in the past. No green turtles were seen during the 1992 survey work in the vicinity of Transects 5 and 6. A short underwater reconnaissance of the usual resting area (a small ledge under a large Porites lobata colony) revealed that the resting site had been completely covered with coral rubble from the hurricane (as had most of the depressions in the surrounding area).

Physical measurements were made on the morning of 22 December 1992. These data are presented in Table 8. Little variation was noted in temperature (22.6 to 22.8°C), percent oxygen saturation (102 to 105%) or salinity (all 34‰) despite the fact that measurements for oxygen and temperature were made both at the surface and about 1 m above the bottom. In all cases the secchi disk measurements did not yield an extinction value; water clarity was such that the disk was still plainly visible on the bottom from the surface. As has been suggested previously, a better method of determining water clarity might be to collect water samples and measure turbidity with a nephalometer in the laboratory.

The biological data for all three surveys (1990, 1991, and 1992) are summarized as means for each transect in Table 9. The 1990 and 1991 data are from Brock (1992a, 1992b). Differences are apparent for some of the parameters between the three years. Some change is evident in the benthic measures (such as coral cover) between the 1991 and 1992 (pre- and post-hurricane) surveys and this is to be expected. Despite these changes the Kruskal-Wallis anova shows that there are no statistically significant changes from the 1990 survey to the most recent 1992 field effort for the mean coral cover at a sample site (P > 0.69, df = 2, N.S.), mean number of coral species at each site (P > 0.28, df = 2, N.S.), mean number of invertebrate species on a transect (P > 0.52, df = 2, N.S.), mean number of individual invertebrates at each location (P > 0.74, df = 2, N.S.), mean number of fish species on a transect (P > 0.36, df = 2, N.S.), mean number of individual fish at a sample site (P > 0.16, df = 2, N.S.), and mean standing crop at a station (P > 0.44, df = 2, N.S.). The Student-Neuman-Keuls multiple range test likewise demonstrated that there are no statistically significant differences among these parameters between the six stations and three sample periods.

The biological parameters measured in the three surveys (i.e., number of coral species, percent cover, number of macroinvertebrate species, number of fish species, number of individual fish and biomass of fishes), point to the fact that the Kewalo Landfill site has the most diverse communities, followed by the Reef Runway. The least diverse appears to be the Kalihi Entrance Channel site; this ranking has not changed over the three surveys. The low biological diversity at the Kalihi Entrance Channel site is not surprising in view of the fact that this station was heavily impacted by the old shallow water outfall until 1978.

From a commercial fisheries standpoint, a number of important species have been encountered in the vicinity of the Kewalo Landfill transects and Reef Runway sites including goatfishes (weke - Mulloides flavolineatus and weke‘ula - M. vanicolensis), amberjack or kahala (Seriola dumerili), emperor or mu (Monotaxis grandoculis), uku (Aprion virescens), and the squirrelfish or menpachi (Myripristes amaenus).

Since their delineation in December 1990, the six transects have been visited on a number of occasions to insure that permanent markers are remaining in place, etc. During these visits reconnaissance surveys have been carried out in the areas surrounding the selected stations. At a minimum, these qualitative surveys have covered about 4 hectares around each of the three sites. These qualitative observations suggest that the marine communities sampled at the three stations are representative of those found in the surrounding areas.

The working hypothesis is that all three study sites, being situated in relatively shallow water, are outside of the zone of influence of the present deep water outfall. However if impacts from the present deep ocean outfall are occurring to the shallow water coral reef areas shoreward of the outfall, our monitoring should be able to quantitatively discern these impacts. Because of bottom time constraints, potential dangers with deep diving and the fact that coral community development is usually greatest in water less than 30 m of depth, the placement of biological monitoring stations was restricted to waters 20 m or less in depth in this study. Monitoring the shallow water stations provides additional information regarding the recovery of these communities to the perturbation of raw sewage released from the old shallow water outfall that was terminated in 1977–78. Dollar’s (1979) study showed that the Kewalo Landfill station was not directly impacted by the old outfall but the Kalihi Entrance Channel station was “acutely” perturbed and the station offshore of the Reef Runway received an “intermediate” level of disturbance. Additionally in the mid-1970’s the reef runway was constructed which must have contributed to the disturbance of benthic communities at this station (Chapman 1979). The results of these impacts are still evident in the average coral cover estimates made at these stations: the mean coverage offshore of the Kalihi Entrance Channel is only 3 percent, at the Reef Runway station it is 4 percent, and offshore of the Kewalo Landfill it is 23 percent.

The shallow marine ecosystem fronting Sand Island and Honolulu has received considerable perturbation from human activity over the last 100 years. Among the disturbing influences was the disposal of raw sewage effluent in shallow water between the 1930’s and 1977–78 when the deep ocean outfall became operational. In the period from 1955 through 1977 the shallow outfall released 3 m³/sec (62 mgd). Dollar (1979) noted two distinct zones of impact to marine communities: the area of “acute” perturbation was an ellipse 500 m to the east and 1000 m to the west of the outfall. Outside of this area the impacts were evident in a decreasing gradient with distance from the outfall. The maximal extent of impact attributed to this sewage input was 1.9 km to the east and 5.8 km to the west of the outfall. The ellipsoid shape of the zone of influence was attributed to the predominant westerly direction of current flow.

The Kewalo Landfill station is 4.75 km east and inshore of the terminus of the deep ocean outfall, the Kalihi Entrance Channel station is about 2.1 km east and inshore of the terminus and the Reef Runway station is about 3.25 km inshore and west of the deep ocean outfall terminus (Fig. 1). Presumably the present outfall releases the sewage below the thermocline and little interaction occurs with the inshore biota. If however the material was carried into inshore waters, impacts to shallow marine communities would occur in those communities situated primarily to the west of the outfall based on Dollar’s (1979) findings.

The Kewalo Landfill station served as a “control” site in this study. Despite the fact that coral coverage and fish community development is greater at this location, the Kewalo Landfill station has received perturbations in the past. The two transects (T-1 and T-2) that sample the Kewalo Landfill site are situated close to an old, non-operable sewage discharge pipe. Operations utilizing this pipe ceased sometime prior to 1955, and the pipe was probably used sometime in the 1940’s (Mr. A. Muranaka, Oceanographic Team, Division of Wastewater Management, City and County of Honolulu). The development of Kewalo Basin and the entrance channel in the mid-1930’s would have created considerable turbidity that probably impacted this site, some 200 m to the west. From the historical perspective, human induced perturbations have occurred in probably all marine communities situated in shallow waters fronting Honolulu over the last 100 years. The Kewalo Landfill site was selected as the “control” site for this study because of relatively diverse coral and fish communities present as well as its location well to the east of the present deep ocean outfall (presumably out of the zone of influence).

On 11 September 1992 the Hawaiian Islands were struck by Hurricane Iniki. The hurricane passed directly over Kaua‘i with sustained winds of 144 mph and gusts to 172 mph resulting in considerable damage to improvements and forests of that island and the west (leeward) coast of O‘ahu. To a lesser extent, high surf caused damage to marine communities along the south, east and west shores of O‘ahu, Kaua‘i, Maui, Lo(¯,a)na‘i and Hawai‘i; this damage was primarily to coral communities. In many areas a large amount of sand and other loose material was moved and/or advected out of the shallow areas (i.e., depths of less than 27 m) into deeper waters. On O‘ahu, storm waves emanating from the southeast were estimated to exceed 6 to 7 m in height and were breaking in water at least 20 m deep (personal observations).

Storm damage to benthic and fish communities is frequently patchy resulting in a mosaic of destruction (personal observations, Walsh 1983) and occasional storm events generating high surf are important factors in determining the structure of Hawaiian coral communities (Dollar 1982). Numerous studies have shown that storm generated surf may keep coral reefs in a non-equilibrium or sub-climax state (Grigg and Maragos 1974; Connell 1978; Woodley et al. 1981; Grigg 1983). Indeed, the large expanses of near-featureless lava or limestone substratum present around much of the Hawaiian Islands at depths less than 30 m attest to the force and frequency of these events (Brock and Norris 1989). These same wave forces also impact fish communities (Walsh 1983).

Hurricane Iniki caused damage to coral communities at all three study sites; the greatest impact occurred to the benthic communities at Station C (Reef Runway) where areas of the Porolithon covered substratum (up to 1 ¥ 2 m in area and up to 0.75 m in depth) were completely removed; other sites were entirely covered with coral rubble at scales from 10 m² to over 30 m². In some cases a “blanket” up to 0.5 m deep of rubble buried coral colonies or has killed the lower portions of larger colonies. The hurricane broke many coral colonies into pieces; some of these have survived where they have lodged into the substratum. These live fragments are responsible for the increase in the number of coral species seen in some quadrats between the pre- (1991) and post-hurricane (present) surveys. This same phenomenon (i.e., live fragments) has also served to lessen the decrease in coral cover encountered in some of the quadrats where coverage was low prior to the storm. Despite these large changes, many of the benthic components survived as shown in the results above. However, since Hawaiian corals are relatively slow growing, it will be years before the impact of this large storm will no longer be evident in the benthic communities of the study sites.

The hurricane also impacted the fish communities at the sample sites. Coral rubble deposited in depressions serves to lessen the rugosity of the submarine topography (i.e., shelter available to fishes). The loss of local shelter causes fishes to move and take up residence elsewhere; at Stations 5 and 6 (Reef Runway) where considerable rubble was present, many of the resident fishes (such as a school of emperor or mu (Monotaxis grandoculis) were no longer on Transect 6 but had moved about 100 m east to an area where the coral and benthic community remained relatively intact.

Despite the impact of Hurricane Iniki, the summary data in Table 9 which spans three years (December 1990 and December 1992) shows that there has been no statistically significant change in the biological parameters measured in this study. The most variable parameters through time have been the number of fish censused and the estimated standing crop of fish; these changes have been greatest at the Kewalo Landfill site. Relative to many other locations in the Hawaiian Islands, the fish community is well developed at the Kewalo Landfill station. The high standing crop estimates in 1990 and 1992 are much greater than found on most coral reefs; the maximum fish standing crop encountered on natural coral reefs is about 200 g/m² (Goldman and Talbot 1975; Brock et al. 1979). There are two explanations for the high biomass of fishes at the Kewalo Landfill site; these are (1) the shelter created by the old sewer pipe locally enhances the fish community and (2) chance encounters with roving predators or planktivorous and/or other schooling species during censuses.

Space and cover are important agents governing the distribution of coral reef fishes (Risk 1972; Sale 1977; Gladfelter and Gladfelter 1978; Brock et al. 1979; Ogden and Ebersole 1981; Anderson et al. 1981; Shulman et al. 1983; Shulman 1984; Eckert 1985; Walsh 1985; Alevizon et al. 1985). Similarly, the standing crop of fishes on a reef is correlated with the degree of vertical relief of the substratum. Thus Brock (1954) using visual techniques on Hawaiian reefs estimated the standing crop of fishes to range from 4 g/m² on sand flats to a maximum of 186 g/m² in an area of considerable vertical relief. If structural complexity or topographical relief is important to coral reef fish communities, then the addition of materials to increase this relief in otherwise barren areas may serve to locally increase the biomass of fish. The additional topographical relief is usually in the form of artificial reefs but any underwater construction activity (such as the deployment of a sewer line) will have a similar effect. The old sewer discharge pipe is set above the seafloor creating considerable local topographical relief (about 2 m high) in an area where the maximum natural vertical relief does not exceed 25 cm. The shelter and high topographical relief must foster greater development of the fish community (see Brock and Norris 1989).

Chance encounters with large roving predators (such as uku, Aprion virescens; mu, Monotaxis grandoculis; kahala, Seriola dumerili; papio, Caranx melampygus or C. orthrogrammus) or schools of planktivorous fishes (opelu, Decapterus macarellus; kala holo, Naso hexacanthus; kala lolo, N. brevirostris; lauwiliwili, Chaetodon miliaris; mamo, Abudefduf abdominalis) or other schooling species (weke, Mulloides flavolineatus) may greatly increase the counts and biomass of a particular transect. The presence of the sewer pipe serves to focus numerous predators and schooling fishes in the vicinity of the two transects at the Kewalo Landfill site and an encounter with these fishes during a census will result in high biomass estimates. Chance encounters with a small school of mu or emperor (Monotaxis grandoculis) at Station 6 (Reef Runway) accounts for 51 percent of the biomass at that station in 1990; on Transect 2 (Kewalo Landfill) the two planktivorous surgeonfishes (kala holo and kala lolo - Naso hexacanthus and N. brevirostris) accounted for 40 percent of the biomass and the two roving predators the kahala (Seriola dumerili) as well as the papio (Caranx orthogrammus) contributed 21 percent to the biomass estimate for that transect in 1990. In 1991 these planktivorous surgeonfishes and some predators were present around Transects 1 and 2 at the Kewalo Landfill site but did not enter the actual census area while the counts were proceeding, thus do not appear in the data. In 1992 the large school of yellowstripe goatfish or weke (Mulloides flavolineatus) that are resident to the old sewer pipe made up 78 percent of the biomass of Transect 1 and 93 percent of the standing crop present on Transect 2.

Making biological measurements underwater can often be a time-consuming process; use of the photographic technique lessens bottom time in measuring coral and other benthic species coverage. However as noted by Brock (1992b) inspection of the results of the coral coverage data from visual appraisal of quadrats in the field relative to the data from the photographic method points out several things. First, mean coral coverage estimates are in reasonable agreement by either method and the regression of visual versus the photographic coverage data show a statistically significant relationship. However, the photo quadrat technique does not discern small coral colonies or other small colonial benthic species such as the soft coral Anthelia edmondsoni; these are easily seen in the field using the visual assessment method. Both methods work but the technique selected should be done so keeping the objectives of the study in mind. This study will continue to use both methods.

In the present survey the photographs for Transects 1–4 were collected in August 1992 and for Transects 5 and 6 in late September. The hurricane struck on 11 September thus the photo quadrat data from stations 5 and 6 represent post-hurricane conditions. The visually assessed (field) quadrat data were all collected after the hurricane. Thus the photo and field quadrat data are not all directly comparable in the 1992 dataset.

The six transects selected for this study show a considerable range in community development that is probably related to past (historical) impacts. Separating the impact of advanced primary treated effluent released at depth from a multitude of other ongoing and historical impacts that have occurred in and to the shallow marine communities fronting Sand Island is difficult at best. The added natural disturbance of Hurricane Iniki on 11 September 1992 is an additional impact to these communities that varies tremendously with location. However, the siting of these permanent stations to capitalize on presumed gradient(s) of impact created by the variety of land derived sources as well as the repeated sampling of these permanent stations should allow delineation of any changes attributable to the Honolulu deep ocean outfall. The sampling of these stations over the first two years (1990–1991) shows that there was little change to the communities over that period of time suggesting that there was no quantitatively definable impact to shallow water benthic and fish communities due to the operation of the Honolulu deep ocean outfall. Many of the changes seen in the 1992 survey appear to be related to the natural storm event that occurred in September of that year.