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Resource Description: NODC Accession # 0000177
Dr. Richard E. Brock, Dr. Roger S. Fujioka, and Dr. James E.T. Moncur
To determine the status of the marine resources in the vicinity of the discharge in an effort to quantitatively ascertain if any impacts are occurring to the coral reef biota.
Station A (Kewalo Landfill) Utilized as a control area. This station lies east of the present deep-ocean outfall in 17.0 to 18.2 m of water. Prevailing currents create a westerly movement of sewage effluent (Dollar 1979), thus the shallow Kewalo Landfill area is probably not directly impacted. At this location, corals occur in areas of emergent limestone. Immediate coverage over short linear distances may exceed 30%. This station is in the vicinity of Dollar's (1979) station 2.
Station B (Kalihi Channel) Located about 120 m east of the Kalihi Entrance Channel in approximately 15.0 m of water. This station is about 900 m west of the bypass (old) outfall in an area heavily impacted by the old (1955 to 1977) shallow-water discharge and is very close to Dollar (1979) station 14. There is emergent limestone at this station, but coral coverage is low (less than 1%).
Station C (Reef Runway) Located in an area of complex limestone substratum in water ranging from 7.5 to 12.0 m in depth fronting Honolulu International Airport's Reef Runway. This station is located close to Brock's (1986) station that was monitored quarterly in 1977-78 (AECOS, Inc. 1979) and again in 1986. It is close to Dollar's (1979) station 19. This station was moderately impacted by the old shallow-water sewage outfall (Dollar 1979).
MATERIALS AND METHODS# The quantitative sampling of macrofauna of marine communities presents a number of problems; many of these are related to the scale on which one wishes to quantitatively enumerate organism abundance. Marine communities in the waters fronting Sand Island may be spatially defined in a range on the order of a few hundred square centimeters (such as the community living in a Pocillopora meandrina coral head) to many hectares (such as areas which are covered by major biotopes). Because considerable interest focuses on visually dominant corals, diurnally exposed macroinvertebrates, and fishes, a sampling program was designed to delineate changes that may be occurring in communities at this scale.
At each station two transect lines were permanently established using metal stakes and plastic-coated no. 14 copper wire. The transects are 20 m in length and have an orientation that is perpendicular to shore. Two transects were established at each location to provide some replication. Both sample approximately the same benthic communities. On each transect are five permanently marked locations (0 m, 5 m, 10 m, 15 m, and 20 m) for the taking of photographs of the benthic communities. Cover estimates were also made in the field with a 1 m x 1 m quadrat placed at the -1 to 0 m, 4 to 5 m, 9 to 10 m, 14 to 15 m, and 19 to 20 m marks on the transect line in each survey.
Fish abundance and diversity are often related to small-scale topographical relief over short linear distances. A long transect may bisect a number of topographical features (e.g., coral mounds, sand flats, and algal beds), thus sampling more than one community and obscuring distinctive features of individual communities. To alleviate this problem, a short transect (20 m in length), which has proved to be adequate for sampling many Hawaii benthic communities (see Brock 1982; Brock and Norris 1989) is used. Information is collected at each transect location using methods including a visual assessment of fishes, benthic quadrats for cover estimates of sessile forms (e.g., algae, corals, and colonial invertebrates), and counts along the transect line for diurnally exposed motile macroinvertebrates. Fish censuses are conducted over a 20 m x 4 m corridor (the permanent transect line). All fishes within this area to the water's surface are counted. A single diver equipped with scuba, slate, and pencil enters the water, then counts and notes all fishes in the prescribed area (method modified from Brock 1954). Besides counting the numbers of individuals of all fishes seen, the length of each is estimated for later use in the estimation of fish standing crop by linear regression techniques (Ricker 1975).
Species-specific regression coefficients have been developed over the last 30 years by the author and others at the University of Hawaii, Naval Undersea Center (see Evans 1974), and the Hawaii Division of Aquatic Resources using weight and body measurements of captured fishes; for many species the coefficients have been developed using sample sizes in excess of a hundred individuals. For the 1990 survey two weeks were allowed to elapse from the time of station selection and marking to the time of the first fish census to reduce the bias caused by wary fishes. The same individual (the author) performs all fish censuses to reduce bias.
Besides frightening wary fishes, other problems with the visual census technique include the underestimation of cryptic species such as moray eels (family Muraenidae) and nocturnal species such as squirrelfishes (family Holocentridae) and bigeyes or oaweoweo (family Priacanthidae). This problem is compounded in areas of high relief and coral coverage that afford numerous shelter sites. Species lists and abundance estimates are more accurate for areas of low relief, although some fishes with cryptic habits or protective coloration, such as scorpionfishes or nohu (family Scorpaenidae) and flatfishes (family Bothidae), might still be missed.
Another problem is the reduced effectiveness of the visual census technique in turbid water. This is compounded by the difficulty of counting fishes that move quickly or are very numerous. Additionally, bias related to the experience of the census taker should be considered in making comparisons between surveys. Despite these problems, the visual census technique is probably the most accurate, nondestructive assessment method currently available for counting diurnally active fishes (Brock 1982).
A number of methods are utilized to quantitatively assess benthic communities at each station, including the taking of photographs at locations marked for repeated sampling through time (each covering 0.67 m2) and the placing of 1 m x 1 m quadrats at marked locations for repeated measurements. Both the photographs and quadrats are used to estimate coverage of corals and other sessile forms. Photographs, which provide a permanent record from which to estimate coverage, were used in the eight most recent surveys (1991 through 1998); the 1 m x 1 m quadrats were used for an in-the-field appraisal of coverage in all surveys. Cover estimates from photographs and quadrats are all recorded as percent cover. Diurnally exposed motile macroinvertebrates greater than 2 cm in some dimension are censused in the same 4 m x 20 m corridor used for the fish counts.
Macrothalloid algae encountered in the 1 m X 1 m quadrats or photographs were quantitatively recorded as percent cover. Emphasis was placed on those species that were visually dominant, and no attempt was made to quantitatively assess the multitude of microalgal species that constitute the algal turf so characteristic of many coral reef habitats.
As requested by permit agencies, divers made simple physical measurements at the three stations while in the field. Measurements of percent oxygen concentration and temperature were made with a YSI Model 57 Oxygen meter, salinity was taken with a hand-held refractometer, and water clarity was determined using a 12-inch secchi disk.
During fieldwork, an effort was made to note the presence of any green sea turtles (a threatened species) and protected marine mammals within or near the study sites.
#INSTRUMENT TYPES: -SCUBA -Visual census -Photography -Percent oxygen concentration and temperature were made with a YSI Model 57 Oxygen meter, salinity was taken with a hand-held refractometer, and water clarity was determined using a 12-inch secchi disk.
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