Non-Random Variability in Functional Composition of Coral Reef Fish Communities along an Environmental Gradient

Changes in the coral reef complex can affect predator-prey relationships, resource availability and niche utilisation in the associated fish community, which may be reflected in decreased stability of the functional traits present in a community. This is because particular traits may be favoured by a changing environment, or by habitat degradation. Furthermore, other traits can be selected against because degradation can relax the association between fishes and benthic habitat. We characterised six important ecological traits for fish species occurring at seven sites across a disturbed coral reef archipelago in Indonesia, where reefs have been exposed to eutrophication and destructive fishing practices for decades. Functional diversity was assessed using two complementary indices (FRic and RaoQ) and correlated to important environmental factors (live coral cover and rugosity, representing local reef health, and distance from shore, representing a cross-shelf environmental gradient). Indices were examined for both a change in their mean, as well as temporal (short-term; hours) and spatial (cross-shelf) variability, to assess whether fish-habitat association became relaxed along with habitat degradation. Furthermore, variability in individual traits was examined to identify the traits that are most affected by habitat change. Increases in the general reef health indicators, live coral cover and rugosity (correlated with distance from the mainland), were associated with decreases in the variability of functional diversity and with community-level changes in the abundance of several traits (notably home range size, maximum length, microalgae, detritus and small invertebrate feeding and reproductive turnover). A decrease in coral cover increased variability of RaoQ while rugosity and distance both inversely affected variability of FRic; however, averages for these indices did not reveal patterns associated with the environment. These results suggest that increased degradation of coral reefs is associated with increased variability in fish community functional composition resulting from selective impacts on specific traits, thereby affecting the functional response of these communities to increasing perturbations.     

Algae sediment dynamics are mediated by herbivorous fishes on a nearshore coral reef

Coral Reefs - Epilithic algae are a ubiquitous component of coral reefs. Components of the epilithic algal matrix (EAM) can have a significant influence on coral settlement and benthic feeding by...     

Seasonal trends and fish-habitat associations around Pari Island, Indonesia: setting a baseline for environmental monitoring

Indonesia is the world??s richest country regarding reef fish diversity. Nevertheless, the reef ichthyofauna of the Indonesian Archipelago remains poorly known, primarily due to a lack of sampling. Coral reefs in the Kepulauan Seribu Marine National Park close to the Indonesian capital Jakarta are under threat by many destructive activities that trigger a loss of habitat and species diversity. This communication: (1) describes the reef fish community structure from three distinct reef habitats in the Pari Island group dominated by Acropora branching corals (ACB), foliose corals (CF) and massive corals (CM), using a number of community properties such as numerical abundance, species richness, diversity, and multivariate similarity; (2) examines the temporal variation of the fish community from the three habitats; and (3) discusses possible implications for the monitoring of qualitative changes in coral reef systems on small islands. During this study, a total of 13 536 individual fishes were counted, representing 205 species belonging to 36 families. In terms of species richness, Pomacentridae was the dominant fish family in ACB and CF sites (40?% and 48.6?%, respectively), and Labridae (27.4?%) was the dominant family in the CM plots. The most species-rich habitat was ACB with 125 species (with Amblyglyphidodon curacao as the most characteristic species), followed by CM and CF with 117 (Thalassoma lunare) and 79 species (Pomacentrus alexanderae), respectively. Average Shannon-Wiener diversity (ln basis) ranged from 2.0?C2.9 (ACB), 2.4?C3.1 (CF), and 2.1?C3.0 (CM), with no significant difference between growth forms. Abundance, species richness and diversity showed significant seasonal variability, but the effects differed between habitats. Multivariate analysis of the reef fish community was able to detect significant differences between species composition and diversity of the reef fish community between sites with different coral growth forms at Pari Island, both when based on species abundances and when aggregated according to trophic categories. It thus constitutes a useful tool to detect qualitative differences of the species-rich Indonesian coral reef ecosystems.     

Mapping coral reefs using consumer-grade drones and structure from motion photogrammetry techniques

We propose a novel technique to measure the small-scale three-dimensional features of a shallow-water coral reef using a small drone equipped with a consumer-grade camera, a handheld GPS and structure from motion (SfM) algorithms. We used a GoPro HERO4 with a modified lens mounted on a DJI Phantom 2 drone (maximum total take-off weight <2 kg) to perform a 10 min flight and collect 306 aerial images with an overlap equal or greater than 90%. We mapped an area of 8380 m², obtaining as output an ortho-rectified aerial photomosaic and a bathymetric digital elevation model (DEM) with a resolution of 0.78 and 1.56 cm pixel⁻¹, respectively. Through comparison with airborne LiDAR data for the same area, we verified that the location of the ortho-rectified aerial photomosaic is accurate within ~1.4 m. The bathymetric difference between our DEM and the LiDAR dataset is −0.016 ± 0.45 m (1σ). Our results show that it is possible, in conditions of calm waters, low winds and minimal sun glint, to deploy consumer-grade drones as a relatively low-cost and rapid survey technique to produce multispectral and bathymetric data on shallow-water coral reefs. We discuss the utility of such data to monitor temporal changes in topographic complexity of reefs and associated biological processes.

     

Patterns and trends in coral reef macroalgae browsing: a review of browsing herbivorous fishes of the Indo-Pacific

Browsing fishes have been identified as an important component of coral reef resilience, because in contrast to other herbivorous fishes they are able to feed on established macroalgae. Climate change and local anthropogenic impacts have contributed to phase shifts in many coral reefs from coral to macroalgae dominance, and recent research suggests the potential ability of browsers to reverse such phase shifts. However, there is high variation among studies and some contradicting findings exist. Here, we review the relevant literature to assemble a list of species currently known to contribute to browsing in the Indo-Pacific. Furthermore, we identify spatial and temporal patterns, outline factors influencing browsing, and discuss the probability of phase shift reversal. We formulate research recommendations addressing the identified gaps in knowledge about the interactions of browsing fishes and their environment. To date, 37 species of fishes have been observed consuming macroalgae in the Indo-Pacific. The most important groups are the family Siganidae, the subfamily Scarinae (Labridae), and the subfamily Nasinae (Acanthuridae). Browsing species vary between studies depending on location, season and macroalgae species examined. Several influencing factors, such as structural complexity, palatability of macroalgae and ecosystem connectivity have been suggested to cause these discrepancies. The most promising avenues for future research are the effect of structural complexity, the importance of mobile link species and influences of food availability on the selectivity of browsing species. Increasing our knowledge in these fields will provide a better basis for successful management strategies directed at increasing the resilience of coral reefs.     

Poor Performance of Corals Transplanted onto Substrates of Short Durability

Worldwide, coral reefs are degrading due to increasing anthropogenic pressures. Yet, management of reefs still falls short of effectively addressing these threats, and active restoration methods are increasingly being called for. Coral transplantation is frequently advocated as a possible means of coral reef rehabilitation. Fragments produced in coral nurseries or farms have been proposed as a potential source for transplantation, and culture media (inexpensive but non‐durable materials such as wood or bamboo) may serve as transplantation substrate if placed directly in the reef. However, the performance of coral transplants attached to such substrates has not been examined yet. Here, the long‐term survival of transplants attached to bamboo substrates is reported. A total of 6,164 fragments of 4 coral species (Acroporids and Pocilloporids) were monitored for up to 20 months at three sites in North Sulawesi/Indonesia. Bamboo failed as a suitable inexpensive substrate in at least two of the three sites examined. Mortality of transplants 2 years after transplantation was high in three of the four species (67–95%) and was partially linked to substrate disintegration. The results show that, in places were currents or waves threaten to dislocate transplants, a higher effort needs to be directed at a strong and durable attachment of transplanted corals.     

Feeding behavior and diet of the eight-banded butterflyfish Chaetodon octofasciatus in the Thousand Islands,Indonesia

Marine fishes reach their highest diversity in coral reef ecosystems, which they utilize as territory, place of refuge and reproduction, and source of food. One type of predation among reef fishes is feeding on coral polyps, and a single, easily identifiable family of fishes, Chaetodontidae, contains the majority of obligate corallivore species. Multiple studies have examined the behaviour and ecology of Chaetodontidae and their relationship with the benthic habitat. However, many questions remain about their feeding ecology and food specifity at the species level. The present study is the first attempt to systematically decipher the feeding behavior of the obligate corallivore, Chaetodon octofasciatus. Field data were collected from four sites in the Thousand Islands, Indonesia, during two sampling campaigns in 2006, covering two seasons and two different depths. A high abundance of C. octofasciatus was positively related to hard coral cover. Out of a total of 57 scleractinian coral genera observed during the study period, 24 were utilized by C. octofasciatus. All fish collected during the study (n?=?36) had >86 % nematocysts in their guts, supporting their classification as obligate corallivores. Based on the Strauss electivity index, C. octofasciatus displayed a preference for the coral genus Acropora at all depths, while preference for Fungia became more marked at greater depth. Both Acropora and Fungia were observed at high density at all sites, with Acropora density decreasing markedly with depth and Fungia density increasing. Bite rates showed an asymptotic relationship to Acropora density, levelling off between 15 and 20 bites/5 min. The existence of a strong relationship with live coral cover and the preference for specific genera such as Acropora designate C. octofasciatus as a potential bioindicator in the Thousand Islands reefs, while making it particular susceptible to the ongoing degradation of reefs in the region.     

Large-scale production of selected type A trichothecenes: the use of HT-2 toxin and T-2 triol as precursors for the synthesis of <Emphasis Type="Italic">d</Emphasis><Subscript>3</Subscript>-T-2 and <Emphasis Type="Italic">d</Emphasis><Subscript>3</Subscript>-HT-2 toxin

The type A trichothecenes T-2 and HT-2 toxins are toxic secondary metabolites produced by fungi of the Fusarium genus. Their occurrence in cereals, especially in oats, implies health risks for the consumer. Therefore, it is an important task to develop selective and sensitive methods for the analysis of T-2 and HT-2 toxins, and to undertake further studies on their stability and toxicity. Although most toxins are commercially available, their high prices are the limiting factor on the realization of these experiments. Thus, we developed a method for large-scale production of T-2 and HT-2 toxin as well as T-2 triol and T-2 tetraol. T-2 toxin was obtained in gram quantities by biosynthetic production with cultures of F. sporotrichioides. As HT-2 toxin was only formed as a by-product, and T-2 triol and T-2 tetraol were not generated, these compounds were produced by alkaline hydrolysis of T-2 toxin. Separation and isolation of crude toxins was achieved by fast centrifugal partition chromatography (FCPC), which is an efficient tool for the large-scale purification of natural products. Using this fast and yield effective technique, several hundred milligrams of HT-2 toxin, T-2 triol, and T-2 tetraol were obtained. Subsequent, HT-2 toxin and T-2 triol were used for the large-scale synthesis of isotope-labeled T-2 and HT-2 toxin, respectively. Using these standards, an isotope dilution-(ID)-HPLC-MS/MS method for the quantification of T-2 and HT-2 toxin in different matrices was developed.     

Influence of predation risk on the sheltering behaviour of the coral-dwelling damselfish, <Emphasis Type="Italic">Pomacentrus moluccensis</Emphasis>

Predation is a key ecosystem function, especially in high diversity systems such as coral reefs. Not only is predation one of the strongest top-down controls of prey population density, but it also is a strong driver of prey behaviour and function through non-lethal effects. We ask whether predation risk influences sheltering behaviour of damselfish living in mutualism with branching corals. Host corals gain multiple advantages from the mutualistic relationship which are determined by the strength of damselfish sheltering. Distance travelled by the Lemon Damselfish Pomacentrus moluccensis away from their host colony was measured here as a proxy for sheltering strength and was expected to be shortest under highest predation risk. Predation risk, defined as a function of predator abundance and activity, turbidity and habitat complexity, was quantified at four reef slope sites in Kepulauan Seribu, Indonesia. Damselfish sheltering strength was measured using stationary unmanned video cameras. Small damselfish (< 2 cm) increased their sheltering strength under high turbidity. Predator feeding activity, but not abundance, influenced damselfish sheltering strength. Contrary to our expectations, sheltering behaviour of adult damselfish decreased under high predator activity. While these observations are in line with risk-averse behaviour by juvenile P. moluccensis, they may indicate the presence of sentinel behaviour in the adults of this species. Habitat complexity seemed to be less important as a driver of damselfish behaviour. These counterintuitive results may indicate complex social behaviour and age-specific strategies for predator avoidance.     

Global human footprint on the linkage between biodiversity and ecosystem functioning in reef fishes

Difficulties in scaling up theoretical and experimental results have raised controversy over the consequences of biodiversity loss for the functioning of natural ecosystems. Using a global survey of reef fish assemblages, we show that in contrast to previous theoretical and experimental studies, ecosystem functioning (as measured by standing biomass) scales in a non-saturating manner with biodiversity (as measured by species and functional richness) in this ecosystem. Our field study also shows a significant and negative interaction between human population density and biodiversity on ecosystem functioning (i.e., for the same human density there were larger reductions in standing biomass at more diverse reefs). Human effects were found to be related to fishing, coastal development, and land use stressors, and currently affect over 75% of the world's coral reefs. Our results indicate that the consequences of biodiversity loss in coral reefs have been considerably underestimated based on existing knowledge and that reef fish assemblages, particularly the most diverse, are greatly vulnerable to the expansion and intensity of anthropogenic stressors in coastal areas.