Increases in surgeonfish populations after mass mortality of the sea urchinDiadema antillarum in Panamá indicate food limitation

In 1983/1984,Diadema antillarum suffered mass mortalities throughout its West Atlantic range. Its populations were reduced by 95% and subsequently have failed to recover. These die-offs led to sustained increases in the abundance of soft algae, including types eaten by herbivorous reef fishes. I monitored adult populations of three herbivorous surgeonfishes (Acanthurus coeruleus, A. chirurugus andA. bahianus) between 1978 and 1990, and the recruitment of their pelagic juveniles between 1979 and 1989, on six patch reefs in Panamá. Adult populations ofA. coeruleus andA. chirurgus, which largely restrict their feeding to reef substrata, increased by averages of 250 and 160%, respectively, after the die-off ofD. antillarum in 1983. No increases occurred in the adult populations ofA. bahianus, which often feeds in off-reef habitats unaffected byD. antillarum. Average annual levels of juvenile recruitment of all three surgeonfishes did not differ before and after the die-off. These results support the hypothesis that adult populations of two herbivorous fishes that are strongly reliant on reef algae for food previously were limited by competition withD. antillarum.     

Gut characteristics and assimilation efficiencies in two species of herbivorous damselfishes (Pomacentridae: Stegastes dorsopunicans and S. planifrons)

The morphological and physiological mechanisms by which marine herbivores assimilate energy and nutrients from primary producers and transfer them to higher trophic levels of reef ecosystems are poorly understood. Two wide-ranging Caribbean fishes, the dusky damselfish, Stegastes dorsopunicans, and the threespot damselfish, S. planifrons, defend territories on patch reefs in the Archipelago de San Blas, Republic of Panama. We examined how relative intestine length and retention time influence digestion and absorption of energy and nutrients in these fishes. The dusky damselfish has a relative intestine length (RIL=intestine length/standard length) of 1.2 and a Zihler index {ZI=intestine length (mm)/10[mass(g)^1/3]} of 3.4. These values are significantly lower (P_RIL=P_ZI<0.0001) than those for the threespot damselfish (3.0 and 8.2, respectively). Both RIL and ZI for both species fall well below previously published values for other herbivorous pomacentrids, and may reflect their primary food resource at San Blas (diatoms). Energy-rich diatoms may be easier to digest than refractory macroalgae characteristic of diets of many herbivorous fishes (RIL range: 2-20). Despite differences in RIL and ZI between these two species, gut retention time is the same (P>0.05) for both dusky (6.6 h) and threespot damselfish (6.5 h). Thus, food travels the length of the threespot damselfish intestine ~2.5 times faster than it does in the dusky damselfish intestine. Levels of protein, carbohydrate, and lipid are significantly (0.003<P<0.030) higher in the feces of dusky damselfish than in the feces of threespot damselfish, when both species were fed a natural diet of benthic diatoms collected from damselfish territories. This indicates threespot damselfish have a greater nutrient-specific and total assimilation efficiency than do dusky damselfish. Furthermore, when fed an artificial pellet diet, protein absorption efficiency differed significantly (P=0.014) between species; threespot damselfish absorbed 98.3% of dietary protein, whereas dusky damselfish absorbed 96.4% of dietary protein.     

Abundances of surgeonfishes on patch-reefs in Caribbean Panamá: due to settlement,or post-settlement events?

I examined whether patterns of settlement of planktonic juveniles determined the size and composition of adult populations of three Caribbean surgeonfishes (A canthurus bahianus, A. chirurgus and A. coeruleus) on six isolated patch-reefs in Panamá. I monitored settlement monthly on six reefs (0.14 to 0.67 ha) for 8 yr (1978–1986), and censused adults on those reefs annually. Year-to-year fluctuations in the absolute and relative abundances of settlers arriving on each reef were not extreme. Densities of adults in 1986 were not correlated with the densities of settlers that arrived between 1979 and 1984. Survival of settlers, although apparently unrelated to the density of adults, was negatively related to the density of settlers per unit of adult habitat (but not per unit of settlement habitat) for each species. Changes in adult populations of each species between 1978 and 1986 were not correlated with the abundance of settlers relative to the initial number of adults. The relative abundances of adults of each species in 1986 did not reflect the relative abundances of settlers (1979–1984); these abundances were due to both spatial variation and interspecific variation in survival. In some cases, relocation of adults between isolated patch-reefs (as much as 100 m from other reefs) substantially altered the size and composition of surgeonfish populations. Thus, either post-settlement mortality or relocation overrode effects of settlement patterns in determining adult abundances on the six reefs. Relocation is important in organizing reef-fish communities and must be further examined, particularly in large habitat mosaics.     

Effects on growth and reproduction of the coral Stylophora pistillata by the mutualistic damselfish Dascyllus marginatus

Although coral dwelling fishes are common on coral reefs, the nature of their effect on the host corals is poorly understood. The present study, conducted in the Gulf of Eilat (Red Sea) between July 1989 and August 1990, demonstrated that the branching coral Stylophora pistillata (Esper) benefits, in two components of coral fitness, from the presence of the damselfish Dascyllus marginatus (Rüppell), an obligate coral dweller. The growth rate of damselfish-inhabited corals was significantly higher than that of corals without damselfish. This was observed, using two growth assessment methods, in long-term (>7 mo) comparisons between: (1) corals where the damselfish were experimentally removed versus corals with unaltered fish groups; and (2) naturally inhabited versus non-inhabited corals. The presence of damselfish did not affect the coral's specific (per surface area) reproductive output, whether it was assessed by the number of female gonads per polyp or by the number of planulae released cm^-2 surface area d^-1. However, the more rapid increase in branch size in damselfish-inhabited corals resulted in an apparent increase in the total reproductive output, with age, in growing corals. These findings demonstrate that the association between the damselfish D. marginatus and its host coral, S. pistillata, is mutualistic.     

Planktonic larval duration of one hundred species of Pacific and Atlantic damselfishes (Pomacentridae)

The plankton larval duration for 100 species of Pacific and Atlantic damselfishes was estimated from daily growth increments on the otolith of juvenile fish collected at various localities between July 1987 and September 1988. For newly-settled fishes, larval duration was determined by counting the entire number of increments present on the otolith, while for older juveniles estimates were made by counting the number of increments between the center of the otolith and a mark corresponding to settlement. We document the development of otolith formation during the period when eggs are incubated on the reef and show that daily increments are only accreted after larvae hatch and enter the planktonic phase. The planktonic larval duration for damselfish is shorter and less variable, both between and within species, compared to other groups of reef fishes such as wrasses and surgeonfishes. Larval duration ranged from 12 to 39 d. Average duration between species ranged from 13.1 to 35.2 d. The time spent in the plankton was not significantly correlated with geographic distribution when evaluated among species, however, genera with confined regional distribution have a shorter mean larval life than do widely distributed genera. Size at settlement was positively correlated with time spent in the plankton among species, but a significant correlation between these variables was only evident within one of ten species. The low variance in planktonic larval duration within species indicates that most damselfish are unable to delay metamorphosis following competency. This inability to postpone settlement limits the potential for dispersal, especially when dispersal time between suitable habitats is greater than about 30 d.     

The social and mating systems of two labrid fishes,Halichoeres maculipinna and H. garnoti,off the Caribbean coast of Panama

Large males of both species are territorial, particularly when spawning. Small Halichoeres maculipinna (but not H. garnoti) are territorial towards equal sized conspecifics, but not towards dissimilar sized conspecifics or any individuals of an abundant congener. Territoriality of small H. maculipinna may be related to the process of sex-change rather than defense of food. Both sexes of both species, but particularly H. maculipinna, migrate from feeding areas to spawning sites at the edges of reefs at specific times of day. In the two species a large male spawns both with females that live in his feeding area and with many others. Differences in the mating system of H. maculipinna in Panama and Florida seem related to habitat differences at those sites. The relative spatial distributions of feeding and spawning sites may affect (a) whether a female spawns with a large male with whom she feeds, and (b) the ability of large males to monopolize mates at the expense of small males. The spawning success of small males seems to depend on whether large males can penalize their participation in spawning rather than on the ability of small males to predict the occurrence of (and then interfere in) spawnings by large males. In both species, the male-specific color pattern is most intensely exhibited by large males during sexual interactions and tends to be lost when they are being aggressive towards conspecifics. The evolutionary development of such a color pattern in labroid fishes seems to be a response to intersexual rather than intrasexual interactions.     

Comparison of the food of Triphoturus mexicanus and T. nigrescens,two lanternfishes of the Pacific Ocean

Prey (chiefly euphausiids and copepods) eaten by two myctophids (lanternfishes) are compared from incidence in fish stomachs and from abundance in the environment. One lanternfish species, Triphoturus mexicanus, lives in the California Current, and the other, T. nigrescens, lives in the central Pacific Ocean. Although these two environments are very different physically and biologically, the feeding habits of the two lanternfishes are surprisingly similar. Prey biomass is 94% euphausiids, 3% copepods, and 3% other organisms for T. mexicanus and 88% euphausiids, 4.5% copepods, and 7.5% other organisms for T. nigrescens; the difference between the fish species is not significant when tested statistically. The two fishes resemble one another in frequency distributions of ingested copepod individuals, copepod species, euphausiid individuals, and euphausiid species. During a single diurnal feeding period, both fishes eat a variety of copepod species but tend to eat only a single species of euphausiid. T. mexicanus grows to twice the length of T. nigrescens and eats proportionally larger euphausiids; however, both fishes eat copepods having the same median size. The frequencies of euphausiid species in the diets of both fishes differ from the frequencies in the environment. The chief differences between the feeding habits of the two lanternfishes are that T. nigrescens, in comparison to its congener, eats a greater variety of organisms during one diurnal feeding period and captures smaller euphausiids. The feeding patterns for each lanternfish species are consistent over distances of hundreds of kilometers and over many years of sampling.     

Comparison of larval duration and pre- and post-settlement growth in two species of damselfish,Chromis atripectoralis andPomacentrus coelestis (Pisces: Pomacentridae), from the Great Barrier Reef

Light traps were used to capture larval fishes, immediately before settlement, at two localities 500 km apart on the Great Barrier Reef (GBR) in December, 1987. Samples from Lizard Island, in the northern GBR, and Davies Reef, in the central GBR, were dominated by two species of damselfish:Chromis atripectralis andPomacentrus coelestis. Analysis of otoliths revealed significant differences in both size and age at settlement between the two localities forP. coelestis, but not forC. atripectoralis. Growth rates determined for pre- and post-settlementP. coelestis suggested a sigmoidal growth trajectory through the larval life, with growth slowing as fishes approached the time of settlement. Post-settlement growth rates were faster than growth prior to settlement in both species. Growth in both species was, however, similar between localities. The relationship between fish size and otolith size was complex, varying both between pre- and post-settlement fishes, and among localities. This emphasizes the need to validate the relationship between fish size and otolith size before otoliths may be used to back-calculate individual growth trajectories.Contribution No. 500 from the Australian Institute of Marine Science     

Herbivory by the myctophid fish Ceratoscopelus warmingii

During a study of midwater fish feeding in the oligotrophic North Pacific gyre in August 1978, nine specimens of a tropical-subtropical myctophid, Ceratoscopelus warmingii, were found to have been feeding on mats of diatoms, Rhizosolenia spp. Chemical analyses of the intestinal contents of several additional specimens showed significantly elevated levels of diatom degradation products. Therefore, C. warmingii, although known to feed on zooplankton, appears to be adapted for occasional herbivory. Such an adaptation is exceptional within a major ecological group of oceanic fishes that was previously thought to be exclusively carnivorous. Like omnivorous and herbivorous fishes in general, C. warmingii has a longer intestine than other myctophid species. As an adaptive response to competition from a diverse fish fauna in a low-productivity environment, occasional herbivory by C. warmingii runs counter to the theoretical expectation by expanding rather than narrowing the range of potential food types.     

Parrotfish predation on cryptic sponges of Caribbean coral reefs

Some sponge species that live in crevices in the reef frame appear to be restricted to their cryptic habitat by predation. When cryptic sponges were excavated, on Guigalotupo reef, San Blas, Panama, exposing them to potential predators, they were eaten by fishes that are generally considered to be herbivores, primarily parrotfishes of the genus Sparisoma: S.aurofrenatum (Cuvier & Valenciennes), S.viride (Bonnaterre), and S.chrysopterum (Bloch & Schneider). Of the 9150 bites observed to be taken by these species during paired (i.e., with sponges versus without sponges) trials conducted in defined feeding areas during 1986, 1987, and 1988, 72% (i.e. 6581 bites) were on cryptic sponges, even though these were only offered during half of the total observation time and never constituted more than 7% of the cover of the feeding observation areas. Individual parrotfish returned over and over to take bites of the exposed cryptic sponges until they were entirely consumed. They vigorously chased each other away from the sponges, but exhibited no such defense of their usual algal foods. A total of 18 sponge species were tested. Of the cryptic and semi-cryptic sponge species tested, only one of six was rejected by the parrotfish. Two of these six sponge species were consistently consumed entirely, and two were consumed entirely whenever their surfaces were sliced off with a razor blade, demonstrating that these sponges concentrate defenses against predators in their surfaces. One semi-cryptic species and one semi-exposed species were fed upon, but not entirely consumed. By contrast, 11 of 12 of the exposed and semi-exposed species were rejected. Cryptic sponges grew out of their cavities in the reef only when protected by seasonally thick mats of macroalgae or by cages that excluded fish. Received: 10 January 1997 / Accepted: 4 February 1997     

Odd fish abandon mixed-species groups when threatened

Summary In a field experiment, two juvenile size classes of striped parrotfish (Scarus iserti), stoplight light parrotfish (Sparisoma viride), and ocean surgeonfish (Acanthurus bahianus) were threatened by a model of a common predator (the trumpetfish, Aulostomus maculatus) while alone and in mixedspecies groups of 3–100 members. Striped parrotfish, which usually consitute the majority of a group, used the groups for protection. Stopight parrotfish, present in very low numbers, hid in the coral. Individuals of both species left a group sooner if it had fewer conspecifics. Small surgeonfish sought protection in groups, while larger individuals too big to be consumed by the trumpetfish, swam away alone. These results may be explained by differences in the protection derived from mixed-species groups, and particularly, by the high predation risk suffered by odd individuals.     

Development of the nasal olfactory organs in the larvae, settlement-stages and some adults of 14 species of Caribbean reef fishes (Labridae, Scaridae, Pomacentridae)

Larval fishes likely use a variety of settlement cues to locate and navigate toward the habitats they will inhabit as juveniles. Information about the morphology and state of development of the sensory organs of larval stages of fishes provides insight into their capabilities at the time of settlement. The peripheral olfactory organ of wild-caught late-stage larvae and early juveniles and some adults of 14 species of the Caribbean reef fishes wrasses (Labridae), parrot fishes (Scaridae) and damselfish (Pomacentridae) were examined using scanning electron microscopy and compared in terms of settlement specificity. Ages in days after hatching and days post-settlement were determined from the otoliths. Morphology of the nares and the olfactory epithelium are described for these species by stage. The separation of the anterior and posterior nares occurred before settlement in the labrids but in some specimens of scarids this separation was not complete by the time of settlement. Densities of ciliated and microvillous receptor cells and non-sensory ciliated epithelial cells were calculated. Densities of ciliated receptor cells ranged from 0.389 μm⁻² in a specimen of Thallasoma bifasciatum to 0.0057 μm⁻² in Bodianus rufus and of microvillous receptor cells from 0.038 μm⁻² in a Clepticus parrae juvenile to 0.266 μm⁻² in a juvenile Doratonotus megalepis. Densities of non-sensory cilia, also associated with high olfactory ability, were also high. The olfactory organ in wrasses is well developed prior to settlement and is comparable to that of adult fishes. The possible role of olfaction in larval schooling, reef cue detection and orientation toward habitat at settlement is discussed.

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Reef-basel herbivores and the distribution of two seagrasses (Syringodium filiforme and Thalassia testudinum) in the San Blas Islands (Western Caribbean)

Two seagrasses, manatee grass (Syringodium filiforme) and turtle grass (Thalassia testudinum), predominated in the areas bordering Ukkup Tupo, San Blas Islands, Western Caribbean. These seagrasses occupied the following three concentric zones extending outward from the reef: a near-reef turtle grass zone, an intermediate manatee grass zone and an off-reef turtle grass zone. Feeding experiments between January and March 1980 indicate that the absence of manatee grass close to the reef resulted from grazing by reef-associated herbivores, mainly day-active fishes and night-active sea urchins (Diadema antillarum). Grazing on manatee grass by fishes was approximately six times greater than grazing by sea urchins; thus, it appears that herbivorous fishes restrict the near-reef distribution of manatee grass at the study area. Where grazing was heaviest, the inner boundary of the manatee grass zone was farthest from the reef. The volume of manatee grass grazed during experiments was five times the volume of turtle grass consumed, strongly suggesting that the former species is a preferred food item. This is the first evidence for selective grazing on seagrasses.     

Social facilitation of selective mortality

Territorial defense by breeders influences access to resources near defended nest sites by intruder species and may have indirect effects on other species within the territory, leading to local patchiness in distribution patterns. The present study demonstrates that adult males of a damselfish, Pomacentrus amboinensis, indirectly facilitate the increased survival of conspecific juveniles through the territorial defense of their nesting site from potential egg predators. Moreover, male territoriality results in a shift in the selectivity of predation on newly settled juveniles. We monitored the fate of pairs of predator-naive, newly settled P. amboinensis placed inside and outside nesting territories. Individuals within a pair differed in size by approximately 1 mm and were tagged for individual identification. Away from male territories larger juveniles had greater survival, while within territories, larger juveniles suffered higher mortality. Behavioral observations indicated that the moonwrasse Thalassoma lunare, a predator of benthic eggs and small fishes, had reduced access to juveniles within male territories, while another predator on small fishes, the dottyback Pseudochromis fuscus, had unobstructed access to male territories. Experimental removal of P. fuscus indicated that the shift in the direction of phenotypic selection on newly settled juveniles was the indirect effect of aggression by nest-guarding male damselfish, which resulted in differential access to male territories by these two predators of small fishes. Evidence suggests that behavioral interactions between the resident community and intruders will influence patchiness in selective pressures imposed on benthic prey by influencing both the composition of predator types that can access the prey resource and their relative abundance. How this spatial and temporal patchiness in predator pressure interacts with spatial patchiness of recruiting prey will have a major influence on the resulting distribution of juveniles and their phenotypic traits.     

Geographical gradients of marine herbivorous fishes: patterns and processes

We present new data and the first rigorous analysis of latitudinal and thermal gradients of diversity, density and biomass of marine herbivorous fishes and review proposed explanatory mechanisms. Consistently, negative relationships between latitude, and positive relationships between sea surface temperature (SST), and relative richness and relative abundance of herbivorous fishes were found worldwide. Significant differences in the strength of gradients of richness and abundance with latitude and SST between tropical and extratropical zones were found consistently across ocean basins. Standardized sampling along the western Atlantic also showed negative relationships between latitude and total density and biomass. The trends, however, are driven by different components of the fish assemblages (i.e., scarids in the Caribbean and acanthurids in Brazil). Patterns of abundance along thermal gradients, generally associated with extensive latitudinal gradients, also were found at the local scale. Feeding rate of the ocean surgeonfish Acanthurus bahianus decreases with temperature more rapidly than the mean metabolic rate of teleost fishes. This relationship suggests a temperature-related physiological constraint. From the new standardized and comparative data presented and the review of the explanatory hypotheses, we conclude that temperature-related feeding and digestive processes are most likely involved in the distribution patterns of herbivorous fishes. Electronic Supplementary Material Supplementary material is available for this article at     

Sulfide tolerance and detoxification in shallow-water marine fishes

Hydrogen sulfide is a potent inhibitor of aerobic respiration. Sulfide is produced in sediments, and many species of fish live in association with the bottom. Tolerance tests, enzyme assays, and chromatography of sulfur compounds in thirteen species of shallow-water marine fishes (collected in San Diego, California, USA in 1987–1988) indicate adaptations to sulfide that vary with habitat and lifestyle. Tidal-marsh inhabitants, like Gillichthys mirabilis and Fundulus parvipinnis, have higher tolerance to sulfide (96 h LC₅₀ at 525 to 700 M) relative to outer-bay and open-coast inhabitants (surviving <12 h at much lower concentrations). The cytochrome c oxidase of all species shows high activity and susceptibility to sulfide poisoning, with 50% inhibition at 30 to 500 nM in various tissues. The two marsh species are able to survive at sulfide concentrations already inhibitory to their cytochrome c oxidase and fatal to other species. All species detoxify sulfide by oxidizing it to thiosulfate. All have sulfide-oxidizing activity in the blood, spleen, kidney, liver and gills, which correlates significantly with heme content. Thiosulfate appears in the tissues of sulfide-exposed fish and builds up to high concentrations (up to 2 mM) with stronger and longer exposure. Unexposed fish contain little or no thiosulfate. Sulfide is barely detectable in the tissues, even in high-sulfide exposure tests. We suggest that fish blood, in having high sulfide-oxidizing activity and no cytochrome c oxidase, can act as a short-term first line of defense against sulfide, and thus minimize the amount that reaches the vital organs. The results of this study indicate that sulfide is a significant environmental factor influencing the ecological distribution of marine fishes.     

Effects of fish feeding by snorkellers on the density and size distribution of fishes in a Mediterranean marine protected area

Although there is a great deal of evidence to show that supplementary feeding by humans in terrestrial environments causes pronounced changes in the distribution and behaviour of wild animals, at present very little is known about the potential for such effects on marine fish. This study evaluated the consequences of feeding by snorkellers on fish assemblages in the no-take area of the Ustica Island marine protected area (MPA; western Mediterranean) by (1) determining if reef fish assemblage structure is affected in space and time by tourists feeding the fish; (2) assessing the effects of feeding on the abundance of the most common fish species; and (3) assessing the effects of feeding on the size structure of the two most numerically dominant ones. In particular, we hypothesised that both the abundance and the size structure of some fish species would increase at the study site following supplementary feeding, since the additional food provided by humans would make the site more appealing to them. Fish feeding influenced the fish assemblages within the Ustica MPA, and significant spatio-temporal changes occurred. While fish feeding appeared to have no effect on the ornate wrasse Thalassoma pavo, there was a noticeable increase in the number of Oblada melanura and Epinephelus marginatus in the impacted location after feeding. It is very likely that aggregations of fishes that evolve as a result of fish feeding by the public may have negative effects on local populations of fishes and invertebrates that make up their prey. Recreational use of coastal areas and MPAs is increasing elsewhere, making fish feeding a generalised human activity. Accurate information about its effect on the fish assemblage is essential to make responsible management decisions.Communicated by R. Cattaneo-Vietti, Genova     

Ontogeny of space use and diet of two temperate damselfish species, <Emphasis Type="Italic">Parma microlepis</Emphasis> and <Emphasis Type="Italic">Parma unifasciata</Emphasis>

Studies of reef fish herbivory have mainly focused on the impacts and behaviour of adults of tropical species. In this study, the ontogenetic shifts in home range, aggression, feeding rate, diet and gut morphology in juveniles and adults of two temperate territorial damselfishes, Parma microlepis and Parma unifasciata, were determined. Both P. microlepis and P. unifasciata juveniles under 80 mm TL exhibited no aggressive chases towards conspecifics or other species, while above 80 mm TL aggressive chase frequency increased in conjunction with an increase in home range, defended as a territory. Ontogenetic diet shifts, characterised by an increase in herbivory (P. unifasciata: juveniles: 64% plant material, adults: 95% plant material; P. microlepis: juveniles: 43% plant material, adults: 67% plant material) were observed for both species. The ratio of digestive tract length to body length, which often accompanies a switch to herbivory, increased significantly with ontogeny for both species. Compared to tropical confamilial grazers, these temperate damselfish species feeding rates were lower, and they had larger territories which were not as strongly defended (fewer aggressive chases).     

The trophic status of herbivorous fishes on coral reefs

Estimates of feeding rates, alimentary tract structure and temporal patterns of food processing obtained from twelve species of nominally herbivorous fishes on the northern Great Barrier Reef were compared. These included members of the families Acanthuridae, Scaridae and Kyphosidae. Based on an analysis of diet and short-chain fatty acid (SCFA) profiles from a previous study we initially partitioned the twelve species into four dietary categories, as follows: (a) Category 1: herbivores with a diet of macroscopic brown algae and high SCFA profiles in the hindgut region (Naso unicornis, Kyphosus vaigiensis); (b) Category 2: herbivores feeding on turfing and filamentous red and green algae with moderate SCFA profiles in the hindgut region (N. tonganus, K. cinerascens, Zebrasoma scopas, Acanthurus lineatus); (c) Category 3: zooplankton feeders with moderate SCFA profiles (N. vlamingii, N. brevirostris); (d) Category 4: species feeding on detrital and sedimentary materials with low levels of SCFA (Chlorurus microrhinos, Scarus schlegeli, Ctenochaetus striatus, A. olivaceus). The purpose of this comparison was to determine whether measures of feeding activity, alimentary tract structure, and food processing were concordant with diet. A dichotomy in feeding rates was observed. Species with a diet of algae and zooplankton (categories 1–3) had slower feeding rates than those feeding on detrital aggregates and sediment (category 4). The pattern of food processing also followed the same dichotomy with species of categories 1–3 retaining food in the alimentary tract overnight and commencing the feeding day with substantial amounts of food in the intestine and hindgut. Category-4 species commenced the feeding day with empty alimentary tracts suggesting a rapid turnover of gut contents. Within the herbivorous and zooplankton-feeding species neither alimentary tract structure nor food processing mode were predicted by diet or SCFA profiles. A hindgut fermentation chamber was present in K. vaigiensis but not in N. unicornis, a species with high levels of SCFA in the hindgut region and a diet of brown macroscopic algae. In contrast N. vlamingii, with a diet dominated by animal matter, retained large amounts of food material in a hindgut chamber over the entire feeding cycle. In tropical perciform fishes, herbivory and fermentation are not associated with the alimentary tract structures that characterise herbivorous terrestrial vertebrates. Estimates of the abundance of the different groupings of nominally herbivorous fishes indicated that the dominant elements in the reef grazing and browsing fauna were consumers of detrital and sedimentary materials. These could not be classified as herbivores. Members of this group were dominant in all habitats investigated. Explicitly herbivorous taxa were a minority component in all habitats investigated.Communicated by G.F. Humphrey, Sydney     

Combined Effects of Levels of Protection and Environmental Variables at Different Spatial Resolutions on Fish Assemblages in a Marine Protected Area

Abstract: The links between species–environment relations and species’ responses to protection are unclear, but the objectives of marine protected areas (MPAs) are most likely to be achieved when those relations are known and inform MPA design. The components of a species’ habitat vary with the spatial resolution of the area considered. We characterized areas at two resolutions: 250 m² (transect) and approximately 30,000 m² (seascape). We considered three categories of environmental variables: substrate type, bottom complexity, and depth. We sought to determine at which resolution habitat characteristics were a better predictor of abundance and species composition of fishes and whether the relations with environmental variables at either resolution affected species’ responses to protection. Habitat features accounted for a larger proportion of spatial variation in species composition and abundances than differences in protection status. This spatial variation was explained best by habitat characteristics at the seascape level than at the transect level. Species’ responses to protected areas were specific to particular seascape characteristics, primarily depth, and bottom complexity. Our method may be useful for prioritizing marine areas for protection, designing MPAs, and monitoring their effectiveness. It identified areas that provided natural shelter, areas acting as buffer zones, and areas where fish species were most responsive to protection. The identification of such areas is necessary for cost‐effective establishment and monitoring of MPAs.