Chemical stimuli in coral reefs: how butterflyfishes find their food

Animals use sensory stimuli either to assess and select habitats, mates or food, as well as for communication. The present study aimed to understand the behavioural processes enabling several Chaetodon species (butterflyfishes) to locate one of their food sources (epibionts present on pearl oyster shells) at Rangiroa atoll (French Polynesia). Among the five species tested, our 2-channel choice flume chamber experiments identified three species that were attracted to their food source by chemical stimuli. HPLC experiments showed that pearl oysters and epibionts have specific and unique chemical fingerprints, either one or nine specific peaks, respectively. Overall, chemical stimuli are emitted by both epibionts (used directly by Chaetodon auriga, C. lunula and C. citrinellus) and live pearl oysters (used indirectly by C. auriga and C. lunula) to locate their food source. Biosynthesis of these chemical stimuli could be used to artificially attract butterflyfishes to pearl oyster rearing stations in order to increase the natural cleaning of pearl oyster shells and thus reduce one large cost for this aquaculture.     

Declines in the abundance of Chaetodon butterflyfishes following extensive coral depletion

This study documented temporal variation in the abundance of butterflyfishes (Chaetodontidae) at Trunk Reef, on the central Great Barrier Reef, Australia, from May 2000 to March 2005. During this period, live coral cover declined by >90%, mostly due to severe coral bleaching. There were no short-term changes (within 4 months) in the abundance of butterflyfishes following initial declines in live coral cover. Surveys conducted in 2005, however, revealed significant declines in the abundance of Chaetodon baronessa , Chaetodon lunulatus , Chaetodon trifascialis, Chaetodon plebeius and Chaetodon rainfordi , all of which are obligate hard-coral feeders. In contrast, there was no significant change in the abundance of Chaetodon auriga , Chaetodon aureofasciatus , Chaetodon citrinellus , Chaetodon melannotus or Chaetodon vagabundus , which are much less reliant on scleractinian coral for food. Clearly, extensive coral depletion, such as that caused by severe coral bleaching, can have a major effect on the abundance of butterflyfishes. Specific responses of butterflyfishes varied according to their reliance on hard corals for food and their ability to utilize alternate prey types.     

Changes in sociality of butterflyfishes linked to population declines and coral loss

Coral Reefs - Degradation and loss of reef habitat is one of the foremost threats to coral reef fishes, especially for highly specialised species with specific reliance on live corals. Aside from...     

Relative gut lengths of coral reef butterflyfishes (Pisces: Chaetodontidae)

Variation in gut length of closely related animals is known to generally be a good predictor of dietary habits. We examined gut length in 28 species of butterflyfishes (Chaetodontidae), which encompass a wide range of dietary types (planktivores, omnivores, and corallivores). We found general dietary patterns to be a good predictor of relative gut length, although we found high variation among groups and covariance with body size. The longest gut lengths are found in species that exclusively feed on the living tissue of corals, while the shortest gut length is found in a planktivorous species. Although we tried to control for phylogeny, corallivory has arisen multiple times in this family, confounding our analyses. The butterflyfishes, a speciose family with a wide range of dietary habits, may nonetheless provide an ideal system for future work studying gut physiology associated with specialization and foraging behaviors.     

Association of butterflyfishes and stony coral tissue loss disease in the Florida Keys

Coral Reefs - Since 2014, stony coral tissue loss disease (SCTLD) has rapidly spread throughout the Florida reef tract infecting and killing dozens of coral species. Previous studies have found...     

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.     

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.     

Ecology shapes the evolutionary trade‐off between predator avoidance and defence in coral reef butterflyfishes

Antipredator defensive traits are thought to trade‐off evolutionarily with traits that facilitate predator avoidance. However, complexity and scale have precluded tests of this prediction in many groups, including fishes. Using a macroevolutionary approach, we test this prediction in butterflyfishes, an iconic group of coral reef inhabitants with diverse social behaviours, foraging strategies and antipredator adaptations. We find that several antipredator traits have evolved adaptively, dependent primarily on foraging strategy. We identify a previously unrecognised axis of diversity in butterflyfishes where species with robust morphological defences have riskier foraging strategies and lack sociality, while species with reduced morphological defences feed in familiar territories, have adaptations for quick escapes and benefit from the vigilance provided by sociality. Furthermore, we find evidence for the constrained evolution of fin spines among species that graze solely on corals, highlighting the importance of corals, as both prey and structural refuge, in shaping fish morphology.     

Differential consumption of scleractinian and non-scleractinian coral larvae by planktivorous damselfishes

Coral Reefs - Planktivorous fishes are known to consume coral larvae due to their high nutritional value that can benefit both the individual and their progeny. However, how the consumption of...     

Evolutionary history of the butterflyfishes (f: Chaetodontidae) and the rise of coral feeding fishes

Of the 5000 fish species on coral reefs, corals dominate the diet of just 41 species. Most (61%) belong to a single family, the butterflyfishes (Chaetodontidae). We examine the evolutionary origins of chaetodontid corallivory using a new molecular phylogeny incorporating all 11 genera. A 1759‐bp sequence of nuclear (S7I1 and ETS2) and mitochondrial (cytochrome b) data yielded a fully resolved tree with strong support for all major nodes. A chronogram, constructed using Bayesian inference with multiple parametric priors, and recent ecological data reveal that corallivory has arisen at least five times over a period of 12 Ma, from 15.7 to 3 Ma. A move onto coral reefs in the Miocene foreshadowed rapid cladogenesis within Chaetodon and the origins of corallivory, coinciding with a global reorganization of coral reefs and the expansion of fast‐growing corals. This historical association underpins the sensitivity of specific butterflyfish clades to global coral decline.     

The brain organization of butterflyfishes

Synopsis The encephalization indices of angelfishes (Pomacanthidae) and butterflyfishes (Chaetodontidae) are typical of advanced perciform fishes: both families lie in the upper part of the polygon of teleost indices. The chaetodontids seem to be a little more encephalized than pomacanthids. The general morphology of the brains in both families is very similar: small olfactory bulbs, large optic tectum and a cerebellum which covers the brain structures in front of it like a cap. This morphology is shared by another family of the coral reef biotope, the Acanthuridae. The histological architecture is also typical of advanced teleosts, with a cortex-like pallium, a laminated nucleus geniculatus (= pretectalis superficialis), a complex valvula cerebelli and a corpus glomerulosum with a clear neuropile centre. The quantitative analysis of the main subdivisions of the brain, either from relative volumes or from indices, shows small olfactory bulbs (microsmy) but important telencephalic and diencephalic centres, large tectal centres (vision) and large cerebellum (precise locomotion). Many of these peculiarities are shared by other fishes inhabiting coral reefs. The differences between the two families seem to be primarily correlated with food habits: the angelfishes, which are sponge-feeders and may have an overweight due to the ballast of the sponge-skeleton in their digestive tract, and which do not need either such good vision or such precise locomotion to pick up their prey, could be a little less encephalized than the butterflyfishes.     

Molecular phylogenetics of the butterflyfishes (Chaetodontidae): taxonomy and biogeography of a global coral reef fish family

Marine butterflyfishes (10 genera, 114 species) are conspicuously beautiful and abundant animals found on coral reefs worldwide, and are well studied due to their ecological importance and commercial value. Several phylogenies based on morphological and molecular data exist, yet a well-supported molecular phylogeny at the species level for a wide range of taxa remains to be resolved. Here we present a molecular phylogeny of the butterflyfishes, including representatives of all genera (except Parachaetodon) and at least one representative of all commonly cited subgenera of Chaetodon (except Roa sensuBlum, 1988). Genetic data were collected for 71 ingroup and 13 outgroup taxa, using two nuclear and three mitochondrial genes that total 3332 nucleotides. Bayesian inference, parsimony, and maximum likelihood methods produced a well-supported phylogeny with strong support for a monophyletic Chaetodontidae. The Chaetodon subgenera Exornator and Chaetodon were found to be polyphyletic, and the genus Amphichaetodon was not the basal sister group to the rest of the family as had been previously proposed. Molecular phylogenetic analysis of data from 5 genes resolved some clades in agreement with previous phylogenetic studies, however the topology of relationships among major butterflyfish groups differed significantly from previous hypotheses. The analysis recovered a clade containing Amphichaetodon, Coradion, Chelmonops, Chelmon, Forcipiger, Hemitaurichthys, Johnrandallia, and Heniochus. Prognathodes was resolved as the sister to all Chaetodon, as in previous hypotheses, although the topology of subgeneric clades differed significantly from hypotheses based on morphology. We use the species-level phylogeny for the butterflyfishes to resolve long-standing questions regarding the use of subgenera in Chaetodon, to reconstruct molecular rates and estimated dates of diversification of major butterflyfish clades, and to examine global biogeographic patterns.     

Geographic variation in resource use by specialist versus generalist butterflyfishes

Localised patterns of resource use can be constrained by multiple factors. Comparison of resource use at multiple locations with differing resource availability can allow fundamental specialists to be distinguished from species that simply feed predominantly on prey types that are locally abundant. This study investigates geographic variation in the feeding ecology of coral‐feeding butterflyfishes to examine whether patterns of resource use and levels of dietary specialisation vary among distinct locations, corresponding with changes in resource availability. Our specific aims were to investigate whether the dietary niche breadth of four butterflyfishes varies among five geographically separated locations and assess whether each species utilises similar resources in each location. Resource availability and dietary composition of four butterflyfishes were quantified at three sites across each of five geographic locations throughout the Pacific. Niche breadth, niche overlap, and resource selection functions were calculated for each species at each site and compared among locations. Availability of dietary resources varied significantly among locations and sites. Chaetodon vagabundus, C. citrinellus and C. lunulatus had low levels of dietary specialisation and used different resources in each location. Chaetodon trifascialis had high levels of dietary specialisation and used the same few resources in each location. Our results indicate that relative levels of dietary specialisation among different butterflyfishes do hold at larger spatial scales, however, geographical variation in the dietary composition of all butterflyfishes indicates that prey availability has a fundamental influence on dietary composition. Highly specialised species such as C. trifascialis will be highly vulnerable to coral loss as they appear to be largely inflexible in their dietary composition. However, the increased feeding plasticity observed here for C. trifascialis suggests this species may have a greater capacity to respond to coral loss than previously assumed.     

Chronic parrotfish grazing impedes coral recovery after bleaching

Coral bleaching, in which corals become visibly pale and typically lose their endosymbiotic zooxanthellae (Symbiodinium spp.), increasingly threatens coral reefs worldwide. While the proximal environmental triggers of bleaching are reasonably well understood, considerably less is known concerning physiological and ecological factors that might exacerbate coral bleaching or delay recovery. We report a bleaching event in Belize during September 2004 in which Montastraea spp. corals that had been previously grazed by corallivorous parrotfishes showed a persistent reduction in symbiont density compared to intact colonies. Additionally, grazed corals exhibited greater diversity in the genetic composition of their symbiont communities, changing from uniform ITS2 type C7 Symbiodinium prior to bleaching to mixed assemblages of Symbiodinium types post-bleaching. These results suggest that chronic predation may exacerbate the influence of environmental stressors and, by altering the coral-zooxanthellae symbiosis, such abiotic-biotic interactions may contribute to spatial variation in bleaching processes.     

Orientation behavior of butterflyfishes (family Chaetodontidae) on coral reefs: spatial learning of route specific landmarks and cognitive maps

Synopsis Foraging butterflyfishes follow predictable paths as they swim from one food patch to another within their territories and home ranges. The pattern is repeated throughout the day. The behavior is described in species belonging to the coral feeding guild. Habit formation and spatial learning are implicated. Foraging paths are based on learned locations of route specific landmarks. When a coral head is removed the fish look for it in its former location. If pairs of foraging fish are deflected from the path, they resume their routine pattern at the first landmark they encounter. Periodically, fish make excursions of 30 m or more to distant parts of the reef. Usually they follow different paths on the outbound and homeward legs of these excursions. The critical question is: Are the paths novel? If they are, it is evidence for the use of cognitive maps. Certainly fishes living in the highly structured coral reef environment are prime candidates to use cognitive maps in their orientation behavior.     

Prey selection by coral-feeding butterflyfishes: strategies to maximize the profit

Synopsis Factors that structure preferences among food corals were examined for the obligate coral-feeding butterflyfishChaetodon multicinctus. In the field, fish show a simple repetitious pattern of foraging composed of (1) pre-encounter search for coral colonies, and (2) post-encounter inspection/orientation, bite, and consumption of polyps. Rose coral,Pocillopora meandrina, and the massive coral,Porites lobata, were taken in higher proportions than their percentage substrate cover, while finger coral,Porites compressa, was taken in lower proportion. Paired presentations of coral colonies in the lab gave similar results:Poc. meandrina was preferred overPor. lobata which was preferred overPor. compressa. Poc. meandrina tissue had the highest energy content, lowest handling time, and highest profitability. Energy content did not differ amongPorites tissues, but handling time was greater and more inspective eye movements were made while foraging on the branched finger coral,Por. compressa. Experimental manipulation of coral colony morphology indicate preferences amongPorites are most likely structured by handling costs. Predictions of a simple prey-choice foraging model are supported in theC. multicinctus system if abundance of the branched coralPor. compressa is estimated as that available to fishes rather than percentage substrate cover. The relative size and abundance of stinging nematocysts are also consistent with observed foraging patterns in the field, but await immunological confirmation. Coral-feeding butterflyfishes offer unique opportunities to test models of foraging ecology in reef fishes, and the direction of future studies is suggested.     

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.     

Ephemeral hypoxia reduces oxygen consumption in the Caribbean coral Orbicella faveolata

Coral Reefs - Oxygen concentrations in coastal waters have declined globally by 10% since the mid-twentieth century, and ocean warming will further reduce the solubility of oxygen in coastal...