Specialist corallivores dominate butterflyfish assemblages in coral‐dominated reef habitats

This study examined the dietary habits and functional composition of butterflyfishes in the Chagos Archipelago, central Indian Ocean. Eighteen species of butterflyfishes were recorded in Chagos, including six obligate corallivores (Chaetodon bennetti, Chaetodon guttatissimus, Chaetodon meyeri, Chaetodon trifascialis, Chaetodon trifasciatus and Chaetodon zanzibarensis), five facultative corallivores (Chaetodon auriga, Chaetodon falcula, Chaetodon interruptus, Chaetodon kleinii and Chaetodon madagaskariensis), two non‐corallivores (Chaetodon lunula and Chaetodon xanthocephalus) and a further five species (Chaetodon citrinellus, Chaetodon lineolatus, Heimitaurichthys zoster, Heniochus monoceros and Forcipiger flavissimus), for which local dietary habits were not studied. There were marked differences in the abundance of butterflyfishes among sites and between reef zones, mostly associated with variation in abundance of scleractinian corals. Obligate coral‐feeding species (mostly C. trifascialis) dominated across all sites. This study suggests that coral feeding and high levels of dietary specialization contribute to high population‐level fitness among coral reef butterflyfishes. Despite being more vulnerable to habitat disturbances and coral loss, it appears likely that specialist coral‐feeding butterflyfishes are also much more resilient to occasional disturbances, and therefore dominate in a wide range of coral reef habitats.     

The use of specialisation indices to predict vulnerability of coral‐feeding butterflyfishes to environmental change

In the absence of detailed assessments of extinction risk, ecological specialisation is often used as a proxy of vulnerability to environmental disturbances and extinction risk. Numerous indices can be used to estimate specialisation; however, the utility of these different indices to predict vulnerability to future environmental change is unknown. Here we compare the performance of specialisation indices using coral‐feeding butterflyfishes as a model group. Our aims were to 1) quantify the dietary preferences of three butterflyfish species across habitats with differing levels of resource availability; 2) investigate how estimates of dietary specialisation vary with the use of different specialisation indices; 3) determine which specialisation indices best inform predictions of vulnerability to environmental change; and 4) assess the utility of resource selection functions to inform predictions of vulnerability to environmental change. The relative level of dietary specialisation estimated for all three species varied when different specialisation indices were used, indicating that the choice of index can have a considerable impact upon estimates of specialisation. Specialisation indices that do not consider resource abundance may fail to distinguish species that primarily use common resources from species that actively target resources disproportionately more than they are available. Resource selection functions provided the greatest insights into the potential response of species to changes in resource availability. Examination of resource selection functions, in addition to specialisation indices, indicated that Chaetodon trifascialis was the most specialised feeder, with highly conserved dietary preferences across all sites, suggesting that this species is highly vulnerable to the impacts of climate‐induced coral loss on reefs. Our results indicate that vulnerability assessments based on some specialisation indices may be misleading and the best estimates of dietary specialisation will be provided by indices which incorporate resource availability measures, as well as assessing responses of species to changes in resource availability.     

Interspecific variation in distributions and diets of coral reef butterflyfishes (Teleostei: Chaetodontidae)

This study examined within‐reef distributions for 19 species of butterflyfishes (Chaetodontidae) at Lizard Island, northern Great Barrier Reef, Australia, and compared spatial patterns of abundance among species with contrasting diets. Spatial variation in abundance of butterflyfishes was most prominent among physiognomic reef zones mainly due to significant zonation of eight species, including four obligate hard‐coral feeders (Chaetodon trifascialis, Chaetodon baronessa, Chaetodon plebeius and Chaetodon lunulatus) and four generalist species (Chaetodon auriga, Chaetodon citrinellus, Chaetodon kleinii and Chaetodon rafflesi). Distributions of obligate hard‐coral feeders were closely associated with spatial variation in percentage cover of scleractinian corals, but no more restricted compared with facultative hard‐coral feeders or non‐coral feeders. Species with highest dietary specialization (C. trifascialis and C. baronessa), however, exhibited the most pronounced zonation patterns and were restricted to habitats with greatest abundance of their preferred prey. While there are conspicuous links between dietary specialization v. spatial patterns in abundance of butterflyfishes, it remains unclear whether dietary specialization is the cause or consequence of more restricted distributions.     

Differences in demographic traits of four butterflyfish species between two reefs of the Great Barrier Reef separated by 1,200?km

Many species demonstrate variation in life history attributes in response to gradients in environmental conditions. For fishes, major drivers of life history variation are changes in temperature and food availability. This study examined large-scale variation in the demography of four species of butterflyfishes (Chaetodon citrinellus, Chaetodon lunulatus, Chaetodon melannotus, and Chaetodon trifascialis) between two locations on Australia’s Great Barrier Reef (Lizard Island and One Tree Island, separated by approximately 1,200 km). Variation in age-based demographic parameters was assessed using the re-parameterised von Bertalanffy growth function. All species displayed measurable differences in body size between locations, with individuals achieving a larger adult size at the higher latitude site (One Tree Island) for three of the four species examined. Resources and abundances of the study species were also measured, revealing some significant differences between locations. For example, for C. trifascialis, there was no difference in its preferred resource or in abundance between locations, yet it achieved a larger body size at the higher latitude location, suggesting a response to temperature. For some species, resources and abundances did vary between locations, limiting the ability to distinguish between a demographic response to temperature as opposed to a response to food or competition. Future studies of life histories and demographics at large spatial scales will need to consider the potentially confounding roles of temperature, resource usage and availability, and abundance/competition to disentangle the effects of these environmental variables.     

Abundance,diversity, and feeding behavior of coral reef butterflyfishes at Lord Howe Island

Endemic species are assumed to have a high risk of extinction because their restricted geographic range is often associated with low abundance and high ecological specialization. This study examines the abundance of Chaetodon butterflyfishes at Lord Howe Island in the south‐west Pacific, and compares interspecific differences in local abundance to the feeding behavior and geographic range of these species. Contrary to expected correlations between abundance and geographic range, the single most abundant species of butterflyfish was Chaetodon tricinctus, which is endemic to Lord Howe Island and adjacent reefs; densities of C. tricinctus (14.1 ± 2.1 SE fish per 200m²) were >3 times higher than the next most abundant butterflyfish (Chaetodon melannotus), and even more abundant than many other geographically widespread species. Dietary breadth for the five dominant butterflyfishes at Lord Howe Island was weakly and generally negative correlated with abundance. The endemic C. tricinctus was a distinct outlier in this relationship, though our extensive feeding observations suggest some issues with the measurements of dietary breadth for this species. Field observations revealed that all bites taken on benthic substrates by C. tricinctus were from scleractinian corals, but adults rarely, if ever, took bites from the benthos, suggesting that they may be feeding nocturnally and/or using mid‐water prey, such as plankton. Alternatively, the energetic demands of C. tricinctus may be fundamentally different to other coral‐feeding butterflyfishes. Neither dietary specialization nor geographic range accounts for interspecific variation in abundance of coral reef butterflyfishes at Lord Howe Island, while much more work on the foraging behavior and population dynamics of C. tricinctus will be required to understand its’ abundance at this location.     

Habitat associations of juvenile versus adult butterflyfishes

Many coral reef fishes exhibit distinct ontogenetic shifts in habitat use while some species settle directly in adult habitats, but there is not any general explanation to account for these differences in settlement strategies among coral reef fishes. This study compared distribution patterns and habitat associations of juvenile (young of the year) butterflyfishes to those of adult conspecifics. Three species, Chaetodon auriga, Chaetodon melannotus, and Chaetodon vagabundus, all of which have limited reliance on coral for food, exhibited marked differences in habitat association of juvenile versus adult individuals. Juveniles of these species were consistently found in shallow-water habitats, whereas adult conspecifics were widely distributed throughout a range of habitats. Juveniles of seven other species (Chaetodon aureofasciatus, Chaetodon baronessa, Chaetodon citrinellus, Chaetodon lunulatus, Chaetodon plebeius, Chaetodon rainfordi, and Chaetodon trifascialis), all of which feed predominantly on live corals, settled directly into habitat occupied by adult conspecifics. Butterflyfishes with strong reliance on corals appear to be constrained to settle in habitats that provide access to essential prey resources, precluding their use of distinct juvenile habitats. More generalist butterflyfishes, however, appear to utilize distinct juvenile habitats and exhibit marked differences in the distribution of juveniles versus adults.     

High gene flow across large geographic scales reduces extinction risk for a highly specialised coral feeding butterflyfish

The vulnerability of ecologically specialised species to environmental fluctuations has been well documented. However, population genetic structure can influence vulnerability to environmental change and recent studies have indicated that specialised species may have lower genetic diversity and greater population structuring compared to their generalist counterparts. To examine whether there were differences in population genetic structure between a dietary specialist (Chaetodon trifascialis) and a dietary generalist (Chaetodon lunulatus) we compared the demographic history and levels of gene flow of two related coral-feeding butterflyfishes. Using allele frequencies of ≥11 microsatellite loci and >350 bases of mitochondrial control region sequence our analyses of C. trifascialis and C. lunulatus from five locations across the Pacific Ocean revealed contrasting demographic histories and levels of genetic structure. Heterozygosity excess tests, neutrality tests and mismatch distributions were all highly significant in the dietary specialist C. trifascialis (all P < 0.01), suggesting genetic bottlenecks have occurred in all locations. In contrast, we found little evidence of genetic bottlenecks for the dietary generalist C. lunulatus. High gene flow and low genetic structuring was detected among locations for C. trifascialis (amova: R(ST) = 0.0027, P = 0.371; Φ(ST) = 0.068, P < 0.0001). Contrary to our expectations, a greater level of genetic structuring between locations was detected for C. lunulatus (amova: R(ST) = 0.0277, Φ(ST) = 0.166, both P < 0.0001). These results suggest that dietary specialisation may affect demographic history through reductions in population size following resource declines, without affecting population structure through reductions in gene flow in the same way that habitat specialisation appears to. Although C. trifascialis is highly vulnerable to coral loss, the high gene flow detected here suggests populations will be able to recover from local declines through the migration of individuals.     

Influence of dietary specialization and resource availability on geographical variation in abundance of butterflyfish

Empirical evidence indicates that both niche breadth and resource availability are key drivers of a species' local abundance patterns. However, most studies have considered the influence of either niche breath or resource availability in isolation, while it is the interactive effects that are likely to influence local abundance. We examined geographic variation in the feeding ecology and distribution of coral-feeding butterflyfish to determine the influence of dietary specialization and dietary resource availability on their local abundance. Dietary composition and abundance of five butterflyfish and coral dietary resource availability were determined at 45 sites across five locations (Lizard Island and Heron Island, Great Barrier Reef; Kimbe Bay, Papua New Guinea; Noumea, New Caledonia; and Moorea, French Polynesia). Multiple regression models using variables representative of total dietary resource availability, availability of specific dietary resources, and interspecific competition were used to determine the best predictors of local abundance across all sites and locations for each species. Factors influencing local abundance varied between butterflyfish with specialized and generalized diets. Dietary resource availability had the strongest influence on the abundance of Chaetodon trifascialis-the most specialized species. Local abundance of C. trifascialis was best predicted by availability of the Acropora corals that it preferentially feeds on. In contrast, abundance of generalist butterflyfish was poorly described by variation in availability of specific resources. Rather, indices of total dietary resource availability best predicted their abundance. Overall, multiple regression models only explained a small proportion of the variation in local abundance for all five species. Despite their relatively specialized diets, dietary resource availability has limited influence on the local abundance of butterflyfish. Only the most specialized species appear to be consistently limited by prey availability. Local and total abundance of species are influenced by a wide range of different factors and there is definite need to conduct independent species assessments.     

Corallivory in tubelip wrasses: diet,feeding and trophic importance

This paper describes a 2 month study of the patterns of abundance, feeding pressure, diet and feeding selectivity in corallivorous tubelip wrasses (Labridae), rarely studied, yet widespread and abundant group of corallivores on Indo‐Pacific coral reefs. The relative abundance and feeding pressure of corallivorous wrasses and butterflyfishes (Chaetodontidae) in Kimbe Bay, Papua New Guinea, were compared. Overall, tubelip wrasses were more than twice as abundant as corallivorous butterflyfishes and accounted for three times as many feeding bites on corals. The three most abundant tubelip wrasses (yellowtail tubelip Diproctacanthus xanthurus, Allen's tubelip Labropsis alleni and the tubelip wrasse Labrichthys unilineatus) were all obligate corallivores taking > 97% of bites from the surface of live corals. Labropsis alleni and D. xanthurus were highly selective, consuming preferred prey species in proportions significantly higher than expected given their availability. In contrast, L. unilineatus was fairly non‐selective and consumed most corals in direct accordance with their availability. As coral predators, tubelip wrasses are highly comparable to coral‐feeding butterflyfishes in the coral species consumed, range of dietary specialization and their reliance on live coral. Tubelip wrasses, however, may supersede butterflyfishes as the predominant corallivorous family in some Indo‐Pacific locations, and coral‐feeding tubelip wrasses are likely to be severely affected by coral decline.     

Monogamy in a feeding generalist, <Emphasis Type="Italic">Chaetodon trichrous</Emphasis>, the endemic Tahitian Butterflyfish

Butterflyfishes have been well studied for their feeding ecology and mating systems. In particular, studies of corallivorous butterflyfishes have supported models of monogamy based on their predictable, low quality food; a patch of coral that is economically defensible by a pair. Moreover, pairs often exhibit trade-offs in territorial defense (greater by males) and feeding (greater by females) that improve their reproductive success. However, this model has not been well tested for more generalist feeders. In addition, recent hypotheses for monogamy in fish have emphasized parental care, but butterflyfishes do not provide parental care. This study tests five hypotheses for monogamy in the endemic Tahitian butterflyfish, Chaetodon trichrous: 1) uniform distribution of limiting resources, 2) joint defense of a territory, 3) low mate availability, 4) predator detection, and 5) benefits of cooperative behavior. Chaetodon trichrous was the most abundant butterflyfish in bays. Pairs jointly patrolled feeding territories. They preferentially fed over hard substrate other than live coral, however, this substrate was available outside of territories. They also ate plankton. Pairs were sorted positively for size, and all pairs were heterosexual. Males were larger than their partners, but females fed at higher rates. These results suggest that C. trichrous is monogamous, but reject the hypotheses that pairs form for joint defense of a territory (pairs swam together), that pairs remain together because of low mate availability (frequent interactions with neighbors), or that pairs form for predator detection (no homosexual pairs). Monogamy in C. trichrous is associated with the uniform distribution of hard substrate, although this resource is not limiting. Further, the higher feeding rate of females may represent a benefit provided by their monogamous mates.     

Influence of Resource Availability on the Foraging Strategies of the Triangle Butterflyfish Chaetodon triangulum in the Maldives

Obligate coral feeders such as many members of the Chaetodontidae family (also known as butterflyfish) often show strong preferences for particular coral species. This is thought to have evolved through natural selection as an energy-maximising strategy. Although some species remain as highly specialised feeders throughout their lifetime, many corallivores show a degree of dietary versatility when food abundance is limited; a strategy described by the optimal foraging theory. This study aimed to examine if, within-reef differences in the feeding regime and territory size of the Triangle Butterflyfish Chaetodon triangulum occurred, as a function of resource availability. Results showed that the dietary specialisation of C. triangulum was significant in both areas of low and high coral cover (χL2² = 2.52 x 102, P<0.001 and χL2² = 3.78 x 102, P<0.001 respectively). Resource selection functions (RSFs), calculated for the two main sites of contrasting coral assemblage, showed that in the resource-rich environments, only two Genera (Acropora and Pocillopora) were preferentially selected for, with the majority of other corals being actively ‘avoided’. Conversely, in territories of lower coral coverage, C. triangulum was being less selective in its prey choice and consuming corals in a more even distribution with respect to their availability. Interestingly, coral cover appeared to show no significant effect on feeding rate, however it was a primary determinant of territory size. The findings of the study agree with the predictions of the optimal foraging theory, in that where food supply is scarce, dietary specialisation is minimised and territory size increased. This results in maximising energy intake. This study represents the first scientific evidence that C. triangulum is an obligate corallivore and, as with many other butterflyfish, is therefore dependent on healthy scleractinian corals for survival.     

Cross-species amplification of 44 microsatellite loci developed for Chaetodon trifascialis, C. lunulatus and C. vagabundus in 22 related butterflyfish species

Forty‐four microsatellite primers developed for three species of butterflyfish were cross‐tested against 22 related confamilial species. Amplification success and cross‐species transferability of these markers were moderately high. Between 24 and 37 loci were amplified successfully in each species, with a mean success rate per species of 71.7% (± 1.8 SE). Rates of amplification success were comparable among primers designed for the three source species, ranging from a mean success rate per species of 16.9 loci (± 0.8 SE) for Chaetodon trifascialis source loci to 13.7 loci (± 1.5 SE) for C. vagabundus source loci. Polymorphism rates were high (76.1%± 3.1 SE of all successfully amplified loci), and 10 loci were polymorphic in all successfully amplified species (Tri14, B11, C5, D3, D113, D6, D117, D120, D111, D118). The number of alleles per polymorphic locus ranged from 2 to 8, and the average number of alleles across all polymorphic loci and all species was 3.6 (± 0.07 SE). Polymorphism rates were higher overall in primers designed for C. vagabundus (89.9%± 3.9 SE). Overall cross‐testing success was lowest for Heniochus chrysostomus, the most phylogenetically divergent species. The significant cross‐testing reported here provides a valuable resource that will enable population genetics studies to be undertaken on a range of butterflyfishes without the need for expensive and time‐consuming de novo microsatellite development.     

Temporal and areal feeding behavior of the butterflyfish,Chaetodon trifascialis,at Johnston Atoll

Synopsis The chevron butterflyfish,Chaetodon trifascialis, is found throughout the Indo-Pacific. It is a territorial, diurnal, corallivore found in close association withAcropora spp. corals. The feeding behavior of 33 individuals was studied over six seasons in three habitats.Chaetodon trifascialis spent one third of its active time feeding. However, there was much individual variation. Fish had significantly higher feeding rates during the early afternoon, and there were no significant differences in the feeding rates between the seasons. Feeding rates were significantly different between the three habitats. TheMontipora-rich habitat had the highest feeding rates (x = 10.74 bites min^-1 ± 0.87, all corals combined) and theAcropora-Montipora mixed habitat had the lowest feeding rates (x = 4.58 bites min^-1 ± 0.63, all corals combined). Females fed significantly more than males. WhileC. trifascialis had been thought to only eatAcropora spp. corals, it occasionally fed onMontipora spp. andPocillopora sp. corals whenAcropora spp. were scarce.Chaetodon trifascialis exhibited patterns predicted by foraging theory of an energy maximizer. Territory sizes were inversely related to food density and feeding rates were inversely related to intruder rates. This is a promising system for future testing of foraging strategy models.     

Cryptic dietary components reduce dietary overlap among sympatric butterflyfishes (Chaetodontidae)

This study used three different methods to ascertain dietary composition for 21 Chaetodontidae species co-occurring on a single fringing reef in Derawan Island, East Kalimantan, Indonesia. The combination of in situ feeding observations, examination of gut contents and stable-isotope analyses was expected to identify previously unresolved prey items that contribute to dietary separation. In situ feeding observations identified five species that feed predominantly on anthozoans ( Chaetodon baronessa , Chaetodon bennetti , Chaetodon lunulatus , Chaetodon punctatofasciatus and Chaetodon speculum ). Stable-isotope ratios for these species, as well as for Chaetodon ornatissimus (for which no feeding observations were completed), were very similar and consistent with diets comprising mostly anthozoans. Feeding observations, however, showed that they mostly fed on different coral species, while the identifiable portion of their gut contents showed clear separation based on cryptic dietary components. For example, C. baronessa and C. bennetti appeared to ingest annelid worms during the course of coral feeding, whereas gut contents of C. punctatofasciatus and C. speculum were dominated by crustaceans. In situ feeding observations further identified the following groups: coral–bottom feeders, bottom feeders, sponge feeders and pelagic feeders, feeding on a wide variety of prey items such as Annelida, Crustacea, Cnidaria, Mollusca and macroalgae. Overall, many chaetodontid species had similar reliance on major prey items ( e.g . anthozoans or polychaetes) but differed greatly in the minor prey items that they utilized. Partitioning of minor prey items may be important in reducing interspecific competition and facilitating coexistence of chaetodontids on coral reefs.     

Only the largest terrestrial carnivores increase their dietary breadth with increasing prey richness

1. Animals should adapt their foraging habits, changing their dietary breadth in response to variation in the richness and availability of food resources. Understanding how species modify their dietary breadth according to variation in resource richness would support predictions of their responses to environmental changes that alter prey communities.
2. We evaluated relationships between the dietary breadth of large terrestrial carnivores and the local richness of large prey (defined as the number of species). We tested alternative predictions suggested by ecological and evolutionary theories: with increasing prey richness, species would (1) show a more diverse diet, thus broadening their dietary breadth, or (2) narrow their dietary breadth, indicating specialisation on a smaller number of prey.
3. We collated data from 505 studies of the diets of 12 species of large terrestrial mammalian carnivores to model relationships between two indices of dietary breadth and local prey richness.
4. For the majority of species, we found no evidence for narrowing dietary breadth (i.e. increased specialisation) with increasing prey richness. Although the snow leopard and the dhole appeared to use a lower number of large prey species with increasing prey richness, larger sample sizes are needed to support this result.
5. With increasing prey richness, the five largest carnivores (puma Puma concolor, spotted hyaena Crocuta crocuta, jaguar Panthera onca, lion Panthera leo, and tiger Panthera tigris), plus the Eurasian lynx Lynx lynx and the grey wolf Canis lupus (which are usually top predators in the areas from which data were obtained), showed greater dietary breadth and/or used a greater number of large prey species (i.e. increased generalism).
6. We suggest that dominant large carnivores encounter little competition in expanding their dietary breadth with increasing prey richness; conversely, the dietary niche of subordinate large carnivores is limited by competition with larger, dominant predators. We suggest that, over evolutionary time, resource partitioning is more important in shaping the dietary niche of smaller, inferior competitors than the niche of dominant ones.

     

Seasonal variations in food resource partitioning among four sympatric gudgeon species in the upper Yangtze River

Knowledge of food resource partitioning among sympatric fish species is crucial for understanding the potential mechanisms of species coexistence. Gudgeons (Teleostei: Cyprinidae: Gobioninae) often dominate fish assemblages in the upper Yangtze River. However, little research has been conducted on their trophic interactions. In this paper, seasonal diet and feeding strategy variations of four sympatric gudgeon species, Coreius guichenoti, Coreius heterodon, Rhinogobio ventralis, and Rhinogobio cylindricus, were investigated by analysis of intestinal tract contents, aiming to explore whether food resource partitioning occurred among them. Fish specimens were collected during spring (April–May) and autumn (August–October) in 2010 in Hejiang, a free‐flowing stretch of the upper Yangtze River. Coreius guichenoti, C. heterodon, and R. cylindricus showed omnivorous feeding habits, while R. ventralis exhibited an obligate carnivore feeding habit. Diet overlap among the four studied species was high, especially in spring. However, changes in feeding strategies were observed in autumn. Specifically, C. guichenoti and R. cylindricus expanded their dietary niche breadth and consumed detritus, Sinopotamidae or Hydropsychidae as important complementary food resources. In contrast, C. heterodon and R. ventralis reduced their dietary niche breadth and became more specialized on mussels (Limnoperna lacustris). These results confirmed that sympatric fish species can coexist with high diet overlap, and food resource partitioning among these species may also fluctuate with the seasons.     

Toxic coral gobies reduce the feeding rate of a corallivorous butterflyfish on Acropora corals

The obligate coral-dwelling gobiid genus Gobiodon inhabits Acropora corals and has developed various physiological, morphological and ethological adaptations towards this life habit. While the advantages of this coral-fish association are well documented for Gobiodon, possible fitness-increasing factors for the host coral are unknown. This study examines the influence of coral-dwelling gobies on the feeding behaviour of obligate corallivorous butterflyfishes. In an aquarium experiment using video observation, the corallivorous butterflyfish Chaetodon austriacus fed significantly less on corals inhabited by two Gobiodon species compared to unoccupied coral colonies of similar size. The more agonistic species G. histrio, which mostly displayed directed movements towards butterflyfishes, decreased butterflyfish bite rate by 62–98 % compared to uninhabited colonies. For Gobiodon sp. 3, which mostly displayed undirected movements in response to visits by C. austriacus, bite rate reduction was 64–68 %. The scale-less skin of Gobiodon spp. is covered by mucus that is toxic and multi-functional by reducing predation as well as affecting parasite attachment. A choice flume experiment suggests that the highly diluted skin mucus of Gobiodon spp. also functions as a corallivore repellent. This study demonstrates that Gobiodon spp. exhibit resource defence against coral-feeding butterflyfishes and also that coral colonies without resident Gobiodon suffer higher predation rates. Although the genus Gobiodon is probably a facultative corallivore, this study shows that by reducing predation on inhabited colonies by other fishes, these obligate coral-dwellers either compensate for their own fitness-decreasing impact on host colonies or live in a mutualistic association with them.     

Effects of juvenile coral-feeding butterflyfishes on host corals

Corals provide critical settlement habitat for a wide range of coral reef fishes, particularly corallivorous butterflyfishes, which not only settle directly into live corals but also use this coral as an exclusive food source. This study examines the consequences of chronic predation by juvenile coral-feeding butterflyfishes on their specific host corals. Juvenile butterflyfishes had high levels of site fidelity for host corals with 88% (38/43) of small (<30 mm) juveniles of Chaetodon plebeius feeding exclusively from a single host colony. This highly concentrated predation had negative effects on the condition of these colonies, with tissue biomass declining with increasing predation intensity. Declines were consistent across both field observations and a controlled experiment. Coral tissue biomass declined by 26.7, 44.5 and 53.4% in low, medium and high predation intensity treatments. Similarly, a 41.7% difference in coral tissue biomass was observed between colonies that were naturally inhabited by juvenile butterflyfish compared to uninhabited control colonies. Total lipid content of host corals declined by 29–38% across all treatments including controls and was not related to predation intensity; rather, this decline coincided with the mass spawning of corals and the loss of lipid-rich eggs. Although the speed at which lost coral tissue is regenerated and the long-term consequences for growth and reproduction remain unknown, our findings indicate that predation by juvenile butterflyfishes represents a chronic stress to these coral colonies and will have negative energetic consequences for the corals used as settlement habitat.     

Environmental determinants of butterflyfish social systems

Synopsis Butterflyfishes (Chaetodontidae) display a variety of social systems, including monogamous pair-bonds, harems, and schooling with group spawning. The range of reproductive options available to butterflyfishes is shaped by their general life history characteristics, such as broadcast spawning with widely dispersed pelagic larvae, large body size and low adult mortality. The distribution and quality of food resources are major determinants of group size and mobility, thereby influencing the relative costs and benefits of available options, and determining specific social systems. Planktivorous and corallivorous butterflyfishes exemplify the relationship between food resources and social systems. Pelagic plankton is a patchy, but temporally and spatially unpredictable food resource which is efficiently exploited by fish in mobile schools. Neither sex is able to monopolize food resources necessary for the other sex, and plantivorous butterflyfishes appear constrained to spawn in groups. In contrast, corals are stable and predictable in space and time, favoring residence in one area and territorial defense of that space by coral-feeding butterflyfishes. Females defend food resources from other females, and males defend territories containing a female from other males. Males attempt to defend areas containing more than one female, but are unsuccessful. A monogamous social system results. This system favors the evolution of cooperative behavior between mates to increase female fecundity, as long as the male has an opportunity of sharing in that reproduction. Mate removal experiments conducted on two monogamous coral-feeding species,Chaetodon multicinctus andChaetodon quadrimaculatus reveal a division of labor between male and female pair-mates. Paired males assume most of the territorial defense activities, allowing their mates to feed more.     

Territoriality of the omnivorous butterflyfish, Chaetodon auriga (Chaetodontidae)

Butterflyfish research has focused on corallivorous species, with little attention paid to the other, equally abundant, omnivorous and planktivorous species. This study sought to explore the nature of ranging behaviour of the omnivorous butterflyfish, Chaetodon auriga, across two geographic regions. Pairs of C. auriga defended non-overlapping territories, ranging in area from 97.44 m² to 2281.64 m². Mean territory area varied among study sites while remaining consistent between geographic regions. Most of the variation in territory area was explained by variation in butterflyfish density, while damselfish density, total fish density, and percent sand cover inside territories were also correlated with territory area. Benthic assemblages of territories did not mirror study sites, suggesting that territory establishment is non-random. At all study sites, Chaetodon auriga exhibited significant selection in its patterns of habitat resource use. These results highlight the importance of research on generalist butterflyfishes as damage to coral reef ecosystems continues to threaten their specialist counterparts.