Hawaiian Reef Fishes Research Articles

Assemblage-level effects of the introduced peacock hind (Cephalopholis argus) on Hawaiian reef fishes

The peacock hind Cephalopholis argus (family Serranidae), locally known as ‘roi’, was introduced from French Polynesia to Hawaii in the mid-twentieth century as a food fish. However, because of its association with ciguatera fish poisoning, it is rarely fished for food. Previous research indicates that roi could have a negative impact on native reef fish assemblages because of their high densities and prey consumption rates. However, it is unclear whether roi add to the cumulative mortality of prey (predation hypothesis), or whether predation is instead compensatory (doomed surplus hypothesis). This study experimentally assessed the effects of roi on reef fish populations through a long-term (5.5 year) predator removal experiment. A Before-After-Control-Impact study design was used to assess changes in fish assemblages following the removal of roi on 1.3 ha of patch reef. Increases in the density of prey-sized fish (<15 cm TL) were observed 18 months after roi removal. However, those effects did not translate into sustained increases in prey. While increases in potential competitors, wrasses (family Labridae), particularly the piscivorous ringtail wrasse Oxycheilinus unifasciatus, were observed on roi-free reefs, the fish assemblage did not diverge substantially in composition. Native reef fish appeared to resist the potential negative impacts of predation by roi, possibly through a refuge in size for some fish families. Management to protect intact fish assemblage size-structure could serve to bolster native resistance to invading species. In considering the threats facing coral reefs, and the possible solutions, roi removal alone will not likely replenish native fishery resources.

Comparative phylogeography of the western Indian Ocean reef fauna

Assessing patterns of connectivity at the community and population levels is relevant to marine resource management and conservation. The present study reviews this issue with a focus on the western Indian Ocean (WIO) biogeographic province. This part of the Indian Ocean holds more species than expected from current models of global reef fish species richness. In this study, checklists of reef fish species were examined to determine levels of endemism in each of 10 biogeographic provinces of the Indian Ocean. Results showed that the number of endemic species was higher in the WIO than in any other region of the Indian Ocean. Endemic species from the WIO on the average had a larger body size than elsewhere in the tropical Indian Ocean. This suggests an effect of peripheral speciation, as previously documented in the Hawaiian reef fish fauna, relative to other sites in the tropical western Pacific. To explore evolutionary dynamics of species across biogeographic provinces and infer mechanisms of speciation, we present and compare the results of phylogeographic surveys based on compilations of published and unpublished mitochondrial DNA sequences for 19 Indo-Pacific reef-associated fishes (rainbow grouper Cephalopholis argus, scrawled butterflyfish Chaetodon meyeri, bluespot mullet Crenimugil sp. A, humbug damselfish Dascyllus abudafur/Dascyllus aruanus, areolate grouper Epinephelus areolatus, blacktip grouper Epinephelus fasciatus, honeycomb grouper Epinephelus merra, bluespotted cornetfish Fistularia commersonii, cleaner wrasse Labroides sp. 1, longface emperor Lethrinus sp. A, bluestripe snapper Lutjanus kasmira, unicornfishes Naso brevirosris, Naso unicornis and Naso vlamingii, blue-spotted maskray Neotrygon kuhlii, largescale mullet Planiliza macrolepis, common parrotfish Scarus psicattus, crescent grunter Terapon jarbua, whitetip reef shark Triaenodon obesus) and three coastal Indo-West Pacific invertebrates (blue seastar Linckia laevigata, spiny lobster Panulirus homarus, small giant clam Tridacna maxima). Heterogeneous and often unbalanced sampling design, paucity of data in a number of cases, and among-species discrepancy in phylogeographic structure precluded any generalization regarding phylogeographic patterns. Nevertheless, the WIO might have been a source of haplotypes in some cases and it also harboured an endemic clade in at least one case. The present survey also highlighted likely cryptic species. This may eventually affect the accuracy of the current checklists of species, which form the basis of some of the recent advances in Indo-West Pacific marine ecology and biogeography.

Length-based assessment of coral reef fish populations in the main and northwestern Hawaiian islands.

The coral reef fish community of Hawaii is composed of hundreds of species, supports a multimillion dollar fishing and tourism industry, and is of great cultural importance to the local population. However, a major stock assessment of Hawaiian coral reef fish populations has not yet been conducted. Here we used the robust indicator variable “average length in the exploited phase of the population ()”, estimated from size composition data from commercial fisheries trip reports and fishery-independent diver surveys, to evaluate exploitation rates for 19 Hawaiian reef fishes. By and large, the average lengths obtained from diver surveys agreed well with those from commercial data. We used the estimated exploitation rates coupled with life history parameters synthesized from the literature to parameterize a numerical population model and generate stock sustainability metrics such as spawning potential ratios (SPR). We found good agreement between predicted average lengths in an unfished population (from our population model) and those observed from diver surveys in the largely unexploited Northwestern Hawaiian Islands. Of 19 exploited reef fish species assessed in the main Hawaiian Islands, 9 had SPRs close to or below the 30% overfishing threshold. In general, longer-lived species such as surgeonfishes, the redlip parrotfish (Scarus rubroviolaceus), and the gray snapper (Aprion virescens) had the lowest SPRs, while short-lived species such as goatfishes and jacks, as well as two invasive species (Lutjanus kasmira and Cephalopholis argus), had SPRs above the 30% threshold.

Demographic patterns in the peacock grouper (Cephalopholis argus), an introduced Hawaiian reef fish

This study took advantage of a unique opportunity to collect large sample sizes of a coral reef fish species across a range of physical and biological features of the Hawaiian Archipelago to investigate variability in the demography of an invasive predatory coral reef fish, Cephalopholis argus (Family: Epinephelidae). Age-based demographic analyses were conducted at 10 locations in the main Hawaiian Islands and estimates of weight-at-length, size-at-age, and longevity were compared among locations. Each metric differed among locations, although patterns were not consistent across metrics. Length-weight relationships for C. argus differed among locations and individuals weighed less at a given length at Hilo, the southernmost location studied. Longevity differed among and within islands and was greater at locations on Maui and Hawaii compared to the more northern locations on Oahu and Kauai. Within-island growth patterns differed at Kauai, Oahu, and Hawaii. This work provides a case study of fundamental life history information from distant and/or spatially limited locations that are critical for developing robust fishery models. The differences observed both among and within islands indicate that variability may be driven by cross-scale mechanisms that need to be considered in fisheries stock assessments and ecosystem-based management.

Spatial and vertical patterns in the tidepool fish assemblage on the island of O`ahu

The microtides, wave regimes, and relative isolation of the Hawaiian archipelago may provide unique environmental and biogeographic effects that shape the structure of tidepool fishes. We sampled fishes across a narrow gradient at low tide from 6 sites on the island of O`ahu. We tested predictions of the hypotheses that environmental conditions (pool depth, volume, macroalgal cover, temperature, and salinity) would result in a vertically structured tidepool fish assemblage unique to basalt or limestone rocky shores. 343 fish were recorded from 40 pools, and 19 species from 10 families were identified. Tidepool fish diversity (H’: O`ahu = 2.4; Sites Average = 0.0–0.9) was typical for tropical islands, with members from Gobiidae (5 species), Blenniidae (4 species), Pomacentridae (3 species), Acanthuridae (2 species) and Kuhliidae (2 species) among the most common. Endemism (32%) was higher than other well studied assemblages yet similar to Hawaiian reef fishes (25%). Assemblage abundance varied among shores with basalt or limestone substrate, among sites, and vertically among high, mid, and low pools. In general, blenniids occurred at higher proportions on limestone shores and gobiids were more common on basalt shores. High pools were characterized by an abundance of a small sized (29.0 mm median standard length) blenniid Istiblennius zebra, while the blenniid Entomacrodus marmoratus and wrasses Thalassoma spp. were more common in low pools. Temperature was the best environmental predictor of assemblages and this relationship warrants further investigation. Our findings indicate that assemblages can vary across a narrow geographical range and intertidal shore.

Where are they now? The fates of two genetic lineages in an introduced Hawaiian reef fish

Humans, both wittingly and unwittingly, have been transporting marine organisms beyond their native ranges for centuries (Ruiz et al. 1997). A central challenge of invasion biology is to identify the factors that determine whether introduced species fail to become established, become benign members of a community, or spread so far and reach such densities as to be considered invasive. Organismal features such as physiological tolerance, niche breadth and fecundity are critical, but by themselves are inaccurate predictors of the fates of introduced species (Sakai et al. 2001). The size, age distribution, and genetic makeup of founder populations are also important, but because they are usually unknown they are most often viewed as sources of uncertainty. For marine species with planktonic larvae, the challenge is even greater because the consequences of a planktonic phase for dispersal and population viability are not well understood. In this issue, Gaither et al. (2010a) present a remarkable account of the introduction of a reef fish for which the number and genetic makeup of the founders are known. Between 1956 and 1961, the Division of Fish and Game for the Territory of Hawaii introduced 12 non-indigenous fish species into Hawaiian waters to establish commercial and sport fisheries. The introduction of Lutjanus kasmira, the bluestriped snapper, was the most successful (Fig. 1). There were two releases of fish from French Polynesia. In 1958, 2431 fish from the Marquesas Islands were released on Oahu, followed in 1961 with an additional 728 fish from the Society Islands. The blue striped snapper rapidly spread to the other Hawaiian Islands, reaching the northwestern end of the archipelago by 1992. The choice of the Marquesas as one of two sources for the introduction was fortuitous. Gaither et al. (2010b) found that the Marquesas population is genetically distinct from all other Indo-Pacific populations of L. kasmira. Mitochondrial cytochrome b sequences of fish from the Marquesas belong to a separate lineage that diverged from others in the species roughly half a Ma. Allele frequencies for several nuclear loci are also distinct. This provided Gaither et al. (2010a) with an extraordinary opportunity to examine what became of the mixed genetic heritage of Hawaiian blue striped snappers after 50 years.

Ciguatera in the Introduced Fish Cephalopholis argus (Serranidae) in Hawai‘i and Implications for Fishery Management

The Peacock gouper (Cephalopholis argus) was introduced to Hawai‘i in 1956 to establish a new fishery. It has become abundant, but the fishery failed due to concerns about ciguatera fish poisoning, a neurological disease in humans caused by ingestion of fish containing ciguatoxin. The aim of this study was to provide better understanding of geographic patterns of ciguatoxicity in C. argus and of the correlation of toxicity with morphometric characters of this species, with the goal to assess the possibility of a safe fishery. Overall, 18.2% of C. argus specimens from sites around O‘ahu and Hawai‘i Island contained ciguatoxin in concentrations potentially harmful to humans. This was higher than the rate of occurrence in Hawaiian reef fishes in general, and on the scale of ciguatoxicity in species banned from sale in fish markets. Toxicity was high around both analyzed islands. However, toxic individuals were significantly less common around O‘ahu than around Hawai‘i Island (8% versus 24%). Regular geographic patterns in toxicity within islands (e.g., gradients along coastlines) were not present, and variability in toxicity within each sample site was high. Toxicity was significantly but weakly positively correlated with C. argus length but not with fish condition (measured by length at weight). In conclusion, high prevalence of toxic individuals, variability in toxicity on all analyzed spatial scales, and low explanatory power of morphometric characters make the avoidance of ciguatoxic C. argus individuals difficult. A safe fishery for this species in Hawai‘i therefore does not appear feasible at present.

Relationships between Otolith Size and Body Size for Hawaiian Reef Fishes1

Estimating body size of fishes from remains recovered from piscivores, archaeological sites, and sedimentary deposits is desirable but rarely accomplished because the relationships between the size of a fish and its durable anatomical structures are largely unknown. Regression equations to predict the size or weight of 41 common Hawaiian reef fishes from sagittae (saccular otoliths) are presented. Data are also grouped into higher taxa to permit size predictions when otoliths cannot be assigned to species.

Using bathymetric lidar to define nearshore benthic habitat complexity: Implications for management of reef fish assemblages in Hawaii

Habitat complexity plays a major role in determining the distribution and structure of fish assemblages in the aquatic environment. These locations are critical for ecosystem function and have significant implications for conservation and management. In this study, we evaluated the utility of remotely sensed lidar (light detection and ranging) data for deriving substrate rugosity (a measure of habitat complexity) on a coral reef in Hawaii. We also assessed the potential application of lidar data for examining the relationship between habitat complexity and Hawaiian reef fish assemblage characteristics. Lidar-derived rugosity (4 m grid size) was found to be highly correlated with in-situ rugosity and was concluded to be a viable method for measuring rugosity in analogous coral reef environments. We established that lidar-derived rugosity was a good predictor of fish biomass and demonstrated a strong relationship with several fish assemblage metrics in hard bottom habitat at multiple spatial resolutions. This research demonstrates (i) the efficacy of lidar data to provide substrate rugosity measures at scales commensurate with the resources and their environment (ii) the applicability of lidar-derived rugosity for examining fish–habitat relationships on a coral reef in Hawaii and (iii) the potential of lidar to provide information about the seascape structure that can ultimately be used to prioritize areas for conservation and management.

Spatial and temporal variation in the natal otolith chemistry of a Hawaiian reef fish: prospects for measuring population connectivity

One of the most compelling unanswered questions in marine ecology is the extent to which local populations are connected via larval exchange. Recent work has suggested that variation in the chemistry of otoliths (earstones) of fishes may function as a natural tag, potentially allowing investigators to determine sources of individual larvae and estimate larval connectivity. We analyzed the spatial and temporal variation in natal otolith chemistry of a benthic-spawning reef fish from the Hawaiian Islands. We found no consistent chemical variation at the largest scale (&gt;100 km, among islands), but found significant variation at moderate scales (sites within islands, tens of kilometres) and small scales (clutches within sites), and chemistry of otoliths was not stable between years. These results imply that we may be able to use otolith chemistry to track larval dispersal only if the scales of dispersal match those of variation in natal otolith chemistry, and that separate natal otolith collections may be needed to track different cohorts of larvae. Finally, we found that elemental composition of recruit cores often did not match that of natal otoliths, suggesting that additional methodological development is required before we can effectively apply methods in otolith chemistry to the study of larval dispersal.

Visual Biology of Hawaiian Coral Reef Fishes. II. Colors of Hawaiian Coral Reef Fish

The colors of 51 species of Hawaiian reef fish have been measured using a spectrometer and therefore can be described in objective terms that are not influenced by the human visual experience. In common with other known reef fish populations, the colors of Hawaiian reef fish occupy spectral positions from 300–800nm; yellow or orange with blue, yellow with black, and black with white are the most frequently combined colors; and there is no link between possession of ultraviolet (UV) reflectance and UV visual sensitivity or the potential for UV visual sensitivity. In contrast to other reef systems, blue, yellow, and orange appear more frequently in Hawaiian reef fish. Based on spectral quality of reflections from fish skin, trends in fish colors can be seen that are indicative of both visually driven selective pressures and chemical or physical constraints on the design of colors. UV-reflecting colors can function as semiprivate communication signals. White or yellow with black form highly contrasting patterns that transmit well through clear water. Labroid fishes display uniquely complex colors but lack the ability to see the UV component that is common in their pigments. Step-shaped spectral curves are usually long-wavelength colors such as yellow or red, and colors with a peak-shaped spectral curves are green, blue, violet, and UV.

Visual Biology of Hawaiian Coral Reef Fishes. I. Ocular Transmission and Visual Pigments

Abstract The visual biology of Hawaiian reef fishes was explored by examining their eyes for spectral sensitivity of their visual pigments and for transmission of light through the ocular media to the retina. The spectral absorption curves for the visual pigments of 38 species of Hawaiian fish were recorded using microspectrophotometry. The peak absorption wavelength (λmax) of the rods varied from 477–502 nm and the λmax of individual species conformed closely to values for the same species previously reported using a whole retina extraction procedure. The visual pigments of single cone photoreceptors were categorized, dependent on their λmax-values, as ultraviolet (347–376 nm), violet (398–431 nm) or blue (439–498 nm) sensitive cones. Eight species possessed ultraviolet-sensitive cones and 14 species violet-sensitive cones. Thus, 47% of the species examined displayed photosensitivity to the short-wavelength region of the spectrum. Both identical and nonidentical paired and double cones were found with bl...

Spectral Sensitivity of the Hawaiian Saddle Wrasse, Thalassoma duperrey, and Implications for Visually Mediated Behaviour on Coral Reefs

Although tropical coral reefs are one of the most spectrally complex habitats, there is relatively little known about colour vision of reef fish. In this study, we measured the spectral sensitivity of an endemic Hawaiian coral reef fish, Thalassoma duperrey (family Labridae), and assessed the possible role of visual sensitivity in mediating intraspecific communication. Electrophysiological recordings of compound action potentials from retinal ganglion cells were used to generate spectral sensitivity curves for specific wavelengths (380–620 nm). We found at least 2 sensitivity peaks for the on response (λmax=460, 550 nm). The off response lacked a short wavelength mechanism but a medium wavelength mechanism (λmax=545 nm) and a longwave mechanism (λmax=570 nm) were found. To quantify the visual stimulus provided by a conspecific individual, spectral reflectance from the colour pattern of T. duperrey was measured with a spectroradiometer. Luminance and spectral contrast were computed between colour patches of the pattern and between the patches and natural backgrounds (i.e., water and coral). Reflectance from the blue head and contrast from the blue, green and red patches matched the sensitivity maxima of T. duperrey, although this depended on the type of background. Our results indicate that T. duperrey should be able to visually detect the colour pattern of a conspecific fish and that T. duperrey's visual system is designed to enhance target detection in the coral reef habitat with matched and offset cone mechanisms.

Effects of incident light and background conditions on potential conspicuousness of Hawaiian coral reef fish

Many coral reef fish are assumed to be conspicuous in their natural environment due to their bold and distinct colour patterns. However there have been few attempts to quantify the conspicuousness of coral reef fish under natural photic conditions. In this study, the effects of incident light and background conditions on the potential conspicuousness of four species of Hawaiian reef fish (Chaetodon auriga, Labroides phthirophagus, Thalassoma duperrey, Zebrasoma flavescens) were examined. The optical properties of water, coral and fish colour patterns were measured with an underwater spectroradiometer. Potential conspicuousness was quantified by calculating luminance (brightness) contrast and spectral (colour) contrast within fish colour patterns, and between patterns and natural backgrounds, i.e. water and coral. Under different illuminating and background conditions, the contrast from these fishes was highly variable. Different incident light conditions resulted in significant differences in inherent spectral contrast for L. phthirophagus. All fish had significantly different luminance contrast when the optical properties of the water backgrounds varied. Against coral backgrounds, T. duperrey and Z. flavescens had significantly different luminance contrast and L. phthirophagus and T. duperrey had significantly different spectral contrast. These results have important implications for theories on the adaptive significance of reef fish coloration since the conspicuousness of reef fish appears to be highly dependant on local photic conditions and therefore, some colour patterns may not be conspicuous in the wild as is often presumed.

Evaluation of the Hawaiian reef fishes with the solid phase immunobead assay.

This study presents data on the evaluation of a laboratory ciguatera kit based on the solid phase immunobead assay (SPIA) for the detection of ciguatoxin in Hawaiian reef fish. The SPIA was performed on fish catches by volunteer fishermen throughout the State of Hawaii. A total of 1,067 fish of various species were tested for ciguatoxin (CTX) using the SPIA kit. Of the total 1,067 fish tested, 510 were from Oahu, 402 from Hawaii, and 75 from Maui. The number of fish from Molokai, Kauai, and Lanai were 23, 20, and 7 respectively. Twenty percent of the total fish tested were positive, 41% borderline, and 39% negative for ciguatoxin. The highest percentage of SPIA- positive fish were from Hawaii (27%) followed by Oahu (19%) and Kauai (15%). These results correlate with the reported incidents from the Department of Health (DOH) of actual ciguatera poisoning in the State of Hawaii. Fish in all three categories of the SPIA test values were eaten. No false negatives were noted with individuals eating SPIA negative fish. Of the 232 SPIA borderline values eaten, 3 species of fish caused ciguatera poisoning. These fish included 2 papio, 1 mullet, and 1 po'ou. Of the 17 SPIA positive fish eaten, 5 caused ciguatera poisoning: 2 papio, a kole, an uhu, and a weke. The SPIA ciguatera test did protect the public when only SPIA-negative fish were eaten. The borderline and positive SPIA fish were generally unsafe, especially the positive fish. The data indicated that the probability of getting ciguatera with a SPIA positive fish was 1 out of 3.(ABSTRACT TRUNCATED AT 250 WORDS)

Ocean current variability and the spawning season of Hawaiian reef fishes

The spawning patterns of four Hawaiian reef fishes with similar reproductive habits, but different biogeographic distributions were studied from September 1980 to October 1981. Two species are Hawaiian endemics [Centropyge potteri (Pomacanthidae) and Chaetodon multicinctus (Chaetodontidae)] and the other two have pan-tropical Pacific distributions [Ctenochaetus strigosus and Zebrasoma flavescens (Acanthuridae)]. All showed increased spawning activity from January to July, the prevalent pattern among a majority of coastal marine fishes in Hawaii. Environmental correlatives to the period of peak reproduction include cycles of (a) daylight length and temperature which probably function as proximate cues and (b) seasonal variations in ocean current patterns which may ultimately affect survival of larvae and dispersal. Peak reproduction takes place during months when (1) mesoscale eddies most likely occur, and (2) the probability is greatest of drifting objects remaining near the islands.

Patterns of recruitment and spawning in Hawaiian reef fishes

Recruitment of juvenile fishes to five 25 m2 quadrats on an extensive natural reef in Kona, Hawaii was monitored over 51 months. Pronounced between-year variability in recruit abundance was evident for some species. Many exhibited strikingly low levels of recruitment. Overall recruitment was highly seasonal with a major peak in June and July, and a generally smaller, secondary peak in February and March. Recruitment was minimal during early winter (October–December) and a review of other studies similarly indicates minimal recruitment in Hawaii during this period. Spawning in Hawaiian fishes generally begins during the winter months of relatively low temperatures, increases during late winter and early summer and declines rapidly as maximum summer water temperatures are reached (September–October). Seasonal changes in food availability, ocean currents or salinity seem unlikely to be responsible for observed patterns of recruitment and spawning. Rather, the patterns appear to be most closely tied to changes in water temperature or photoperiod. Loss of propagules to offshore-moving eddies or other unfavorable currents may be responsible for the low levels of juvenile recruitment found in this and other Hawaiian studies. In Kona, at least 6 species of fishes recruited in pulses during quarter or new moon phases. Four other species have been reported elsewhere in Hawaii to recruit during either new or full moon phases. Lunar spawning periodicity was present in fewer than half of the species so far examined, and no single adaptive function for lunar periodicity was applicable to all species.

Behavioral thermoregulation in three Hawaiian reef fishes

The preferred temperature of three Hawaiian coral-reef fishes — Acanthurus triostegus sandvicensis, Abudefduf abdominalis, and Chaetodon multicinctus — were determined in two-chambered tanks that permitted the fish to regulate behaviorally tank temperature. Median selected temperatures over 72 h were as follows: adult C. multicinctus, 24.0° C; juvenile C. multicinctus, 27.0° C; adult Ab. abdominalis, 25.9° C; juvenile Ab. abdominalis, 30.2° C; adult Ac. triostegus, 29.2° C; juvenile Ac. triostegus, 29.3° C. Juvenile Ab. abdominalis selected significantly higher median temperatures than the adults. C. multicinctus and juvenile Ab. abdominalis selected higher median temperatures during the day than at night.

Overgrazing of Algae by Herbivorous Marine Fishes

The growth of benthic algae in the intertidal zone in the Hawaiian Islands is usually luxuriant but in deeper regions, where suitable bottom affords attachment, it is often restricted to a low stubble. The paucity of algae is most evident in reef areas in which the available hard surface for plant growth is restricted by the presence of living coral. Since herbivorous animals of a size greater than a few inches do not graze extensively on algae in the intertidal zone (tides in Hawaii are small), the short length of the thalli on rock or reefs which are always submerged may result from heavy grazing by plant-teeding animals. The dominant herbivores in Hawaiian waters are fishes, especially the surgeonfishes (Acanthuridae) and certain parrottishes (Scaridae). These groups represent the most abundant fishes of moderate size regardless of food habits. Paradoxically, they are still the most abundant in coralliferous areas (an analysis of the populations of Hawaiian reef fishes by underwater transect has been made by Brock 1954). Other important plant-feeders are the omnivorous damselfishes (Pomacentridae) and various echinoids. 'lo test the overgrazing hypothesis, 4 enclosures of oneinch mesh wire one square toot in area were attached to coral-free sections of the rocky bottom of coral-rich Kealakekua Bay near Captain Cook's Monument on the island of Hawaii at depths of 4 to 6 feet in April, 1955. The enclosures prevented larger herbivores from feeding on the algae. Prior to being covered, the small areas were observed to be grazed repeatedly by herbivorous fishes, especially the surgeonfishes Acanthurus leucoparcins, A. antilles and Zebrasotna flavescens. The surgeonfish Ctenochaetus strigosus is at least as common as t^.e above species but it is a detritus feeder and the algae it consumes is mostly already detached from the bottom (Randall 1955). The most abundant acanthurid in inshore waters in Hawaii, Acanthurus triostegus, is not common in areas with high coral cover like the experimental site, probably because it is less inclined than other species of Acanthurus to crop close to the substratum (Randall, 1961). A study site on Hawaii was selected because a comparable area on Oahu is more apt to be disturbed by the many skin divers and fishermen at this more populous island. One month after the enclosures were affixed to the bottcm the author was informed by an acquaintance on