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.N

Habitat associations of juvenile versus adult butterflyfishes

Author Posting. © Springer-Verlag, 2008. This is the author's version of the work. It is posted here by permission of Springer-Verlag for personal use, not for redistribution. The definitive version was published in Coral Reefs 27 (2008): 541-551, doi:10.1007/s00338-008-0357-8.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 utilise distinct juvenile habitats and exhibit marked differences in the distribution of juveniles versus adults.This research was funded by a JCU Program Grant to MSP, while MLB was supported by an NSF (USA) Graduate Research Fellowship

Rare Species Support Vulnerable Functions in High-Diversity Ecosystems

Around the world, the human-induced collapses of populations and species have triggered a sixth mass extinction crisis, with rare species often being the first to disappear. Although the role of species diversity in the maintenance of ecosystem processes has been widely investigated, the role of rare species remains controversial. A critical issue is whether common species insure against the loss of functions supported by rare species. This issue is even more critical in species-rich ecosystems where high functional redundancy among species is likely and where it is thus often assumed that ecosystem functioning is buffered against species loss. Here, using extensive datasets of species occurrences and functional traits from three highly diverse ecosystems (846 coral reef fishes, 2,979 alpine plants, and 662 tropical trees), we demonstrate that the most distinct combinations of traits are supported predominantly by rare species both in terms of local abundance and regional occupancy. Moreover, species that have low functional redundancy and are likely to support the most vulnerable functions, with no other species carrying similar combinations of traits, are rarer than expected by chance in all three ecosystems. For instance, 63% and 98% of fish species that are likely to support highly vulnerable functions in coral reef ecosystems are locally and regionally rare, respectively. For alpine plants, 32% and 89% of such species are locally and regionally rare, respectively. Remarkably, 47% of fish species and 55% of tropical tree species that are likely to support highly vulnerable functions have only one individual per sample on average. Our results emphasize the importance of rare species conservation, even in highly diverse ecosystems, which are thought to exhibit high functional redundancy. Rare species offer more than aesthetic, cultural, or taxonomic diversity value; they disproportionately increase the potential breadth of functions provided by ecosystems across spatial scales. As such, they are likely to insure against future uncertainty arising from climate change and the ever-increasing anthropogenic pressures on ecosystems. Our results call for a more detailed understanding of the role of rarity and functional vulnerability in ecosystem functioning

Cross-scale habitat structure driven by coral species composition on tropical reefs

The availability of habitat structure across spatial scales can determine ecological organization and resilience. However, anthropogenic disturbances are altering the abundance and composition of habitat-forming organisms. How such shifts in the composition of these organisms alter the physical structure of habitats across ecologically important scales remains unclear. At a time of unprecedented coral loss and homogenization of coral assemblages globally, we investigate the inherent structural complexity of taxonomically distinct reefs, across fve ecologically relevant scales of measurement (4–64cm). We show that structural complexity was infuenced by coral species composition, and was not a simple function of coral cover on the studied reefs. However, inter-habitat variation in structural complexity changed with scale. Importantly, the scales at which habitat structure was available also varied among habitats. Complexity at the smallest, most vulnerable scale (4cm) varied the most among habitats, which could have inferences for as much as half of all reef fshes which are small-bodied and refuge dependent for much of their lives. As disturbances continue and species shifts persist, the future of these ecosystems may rely on a greater concern for the composition of habitat-building species and prioritization of particular confgurations for protection of maximal cross-scale habitat structural complexity

Dietary overlap among coral-feeding butterflyfishes (Chaetodontidae) at Lizard Island, northern Great Barrier Reef

This study documented the range of corals,\ud and other prey types, consumed by 20 species of but-\ud terflyfishes, which co-occur at Lizard Island, northern\ud Great Barrier Reef, Australia. Six species (Chaetodon\ud aureofasciatus, C. baronessa, C. lunulatus, C. plebius,\ud C. rainfordi and C. trifascialis) fed almost exclusively\ud on scleractinian corals, and a further eight species\ud (C. citrinellus, C. kleinii, C. lunula, C. melannotus,\ud C. rafflesi, C. speculum, C. ulietensis,and C. unima-\ud culatus) took a significant proportion of their bites\ud from corals. The other six species (C. auriga, C. ep-\ud hippium, C. lineolatus, C. semeion, C. vagabundus, and\ud Chelmon rostratus) rarely consumed coral, but fed on\ud small discrete prey items from non-coral substrates.\ud Coral-feeding butterflyfishes consumed a wide range of\ud corals. Chaetodon lunulatus, for example, consumed 51\ud coral species from 24 different genera. However, there\ud was up to 72% dietary overlap between coral-feeding\ud butterflyfishes, with 11/14 species feeding predomi-\ud nantly on Acropora hyacinthus or Pocillopora dami-\ud cornis. The most specialised corallivore, C. trifascialis,\ud took 88% of bites from A. hyacinthus. Chaetodon tri-\ud fascialis defend territories encompassing one or more\ud colonies of A. hyacinthus, and may have prevented\ud other species such as C. lunulatus from feeding even\ud more extensively on this coral. This study has shown\ud that coexistence of coral-feeding butterflyfishes occurs\ud despite an apparent lack of partitioning of prey\ud resources. While different coral-feeding butterflyfishes\ud were more or less selective in their use of different coral prey, virtually all species fed predominantly on\ud A. hyacinthus or P. damicornis

Assessing reef fish assemblage structure: how do different stereo-video techniques compare?

Quantitative sampling of benthic communities is central to a wide range of ecological research, from understanding spatial distribution and ecology to impact studies. With the need to sample deep as well as shallow regions, limited sampling capabilities of diver-based methods and the expanding footprint of human activity, there is a need for an effective system capable of classifying benthic assemblages and able to monitor potential anthropogenic impacts. Here we describe a remote system capable of collecting benthic photo-quadratsto depths of 100 m. A procedure for the classification of these images into 64 abiotic and biotic categories is also described. During a64-daysamplingprogramthatincludedsamplingatseven locations along 1,200 km of coastline that resulted in the collection of over 9,000 images, only one day of sampling was lost due to equipment malfunction, with 99.5% of points able to be classified to the taxonomic resolution required, demonstrating the reliability and accuracy of this system. Furthermore, the incorporation of differential GPS and ultra-short baseline positioning system allowed collected images to be geo-referenced to within 0.5 m. Such precision allows the system to be used in conjunction with hydroacoustic habitat mapping techniques and potentially for repeated monitoring of areas with a small spatial extent. Development of this system provides a cost-effective means of quantifying benthic assemblages over broad scales

Response of diurnal and nocturnal coral reef fish to protection from fishing: An assessment using baited remote underwater video

Diel variation is known to alter the compositionand structure of reef fish assemblages. What is unknown ishow nocturnal fish assemblages respond to closed fisheryarea management. Diurnal and nocturnal reef fishassemblages at the Houtman Abrolhos Islands, WesternAustralia, were studied using baited remote underwaterstereo-video systems (stereo-BRUVs). Surveys were conductedduring the day and at night (using blue illumination)from three sites inside and three sites outside a closedfishery area (CFA). The relative abundance of 116 fishspecies from 41 families was recorded. Significant changeswere observed in fish assemblage structure from day tonight (driven by high dispersion at night) and in areas openversus closed to fishing (driven by increased abundancewithin the CFA). The effect of protection from fishing wasconsistent for both diurnal and nocturnal fish assemblages.Closer examination of six targeted fish species showed that their response to diel changes and the absence of fishingpressure varied from species to species. The targeted fishesPagrus auratus and Glaucosoma hebraicum were sampledduring the day and at night with both species respondingpositively to protection from fishing. Results suggest thatthe inclusion of diurnal and nocturnal fish assemblage datawill provide an improved ability to assess the effectivenessof closed fishery area management