Influence of coral cover and structural complexity on the accuracy of visual surveys of coral‐reef fish communities

Using manipulated patch reefs with combinations of varying live‐coral cover (low, medium and high) and structural complexity (low and high), common community metrics (abundance, diversity, richness and community composition) collected through standard underwater visual census techniques were compared with exhaustive collections using a fish anaesthetic (clove oil). This study showed that reef condition did not influence underwater visual census estimates at a community level, but reef condition can influence the detectability of some small and cryptic species and this may be exacerbated if surveys are conducted on a larger scale.     

The use of clove oil as an anaesthetic and method for sampling intertidal rockpool fishes

A suitable concentration of clove oil for anaesthetizing eight common Australian intertidal fishes was 40 mg l⁻¹. Induction and recovery times at this concentration varied markedly interspecifically, although were <3 and 5 min, respectively for all but Enneapterygius rufopileus . The number of species in clove oil samples was remarkably similar to bilge pumping samples in both small and large pools, although the number of individuals was significantly lower than bilge pumping in large pools. Number of species and individuals recorded by visual census differed from clove oil and bilge pumping methods in both large and small pools. Failure to detect all fish in pools by clove oil sampling and visual census was due to the secretive behaviour of many species and the tendency for such species as Bathygobius cocosensis not to emerge from under rocks during induction to anaesthesia. Complete draining of pools by bilge pumping, although time consuming, was a more accurate method of sampling rockpool fish assemblages than clove oil. However, clove oil is an effective stand-alone sampling method because the number of fish and individuals are remarkably similar to samples obtained by bilge pumping. Clove oil is a favourable anaesthetic for temperate Australian intertidal fishes as mortality is extremely low, it is inexpensive and user-safe, and induction and recovery times are short, although still sufficient to record biological information and identifications of fish whilst under anaesthesia.     

Anaesthetic effects of clove oil on seven species of tropical reef teleosts

The anaesthetic potential of the clove oil was tested on the following species of tropical reef fishes: Abudefduf saxatilis , Stegastes variabilis , Pareques acuminatus , Acanthurus chirurgus , Sparisoma axillare , Lutjanus apodus and Bathygobius soporator . Induction and recovery times from anaesthesia were compared using various concentrations (20, 30, 40, 50 and 60 mg l⁻¹). Induction and recovery times were not affected by variations in fish total length. When exposed to any of the five tested concentrations of clove oil, specimens achieved a deep state of anaesthesia, with induction and recovery times of <180 and <300 s, respectively. Nevertheless, to maximize safety and reduce fish mortality and stress, the lowest concentration (20 mg l⁻¹) is recommended during field sampling.     

The effects of clove oil on coral: An experimental evaluation using Pocillopora damicornis (Linnaeus)

Clove oil solution (10% clove oil, 90% ethanol) is an anaesthetic that is widely used to catch demersal fish on coral reefs. This study assessed the effects of clove oil solution on colonies of Pocillopora damicornis, a cosmopolitan reef coral. In the laboratory, low concentrations (0.5 ppt) of clove oil solution had no effect on coral colour or photosynthetic efficiency, irrespective of exposure time (1-60 min). Corals treated with high concentrations (50 ppt) of clove oil solution died immediately, including those that were exposed briefly (1 min). Intermediate concentrations (5 ppt) of clove oil solution produced variable results: a 1 min exposure had no effect, a 10 min exposure caused bleaching and reduced photosynthetic efficiency, and a 60 min exposure caused total mortality. To validate these observations, clove oil solution was applied to corals in situ. Sixty-three days after application, corals treated with 10 ml of clove oil solution appeared to be unaffected. It was concluded that (1) limited amounts of clove oil solution are unlikely to harm this coral, and (2) clove oil solution may represent an ‘eco-friendly’ alternative to cyanide for use in the live reef-fish trade.     

Comparative efficacy of clove oil and other chemicals in anaesthetization of Pomacentrus amboinensis, a coral reef fish

The efficacy of quinaldine, benzocaine, MS-222, 2-phenoxyethanol and clove oil was compared for anaesthetizing settlement stage Pomacentrus amboinensis , a frequently studied coral reef fish. Induction to anaesthesia, behaviour during anaesthesia, recovery times and survival rates of fish treated with the different chemicals were compared. Clove oil was only marginally less effective than quinaldine and was more effective than other chemicals tested, except at high concentrations. In addition, fish exposed to clove oil exhibited a much calmer induction to anaesthesia than fish exposed to quinaldine. Therefore, clove oil may be an effective alternative to quinaldine as a fish anaesthetic. Recovery time after anaesthesia with clove oil was two to three times longer than recovery from other chemicals, a desirable charcteristic for use in field studies. Survival rates were excellent for all chemicals.     

The structure of a nearshore fish community of Western Australia: diel patterns and the habitat role of limestone reefs

Synopsis Extensive limestone reefs are a characteristic feature of much of the coastline of Western Australia, and potentially represent a major habitat feature influencing the structure of the coastal fish community. The structure and temporal dynamics of the fish fauna and its relationships to nearshore patch reefs and surrounding habitat near Dongara, Western Australia, were examined using (1) diel gill-netting and (2) quantitative rotenone sampling of enclosed areas of substratum. Long-term and day-to-day variability of the fauna was low. Dominant species of gill-net collections were either associated with reefs or occurred in similar abundances at both reefs and surrounding sand/seagrass flats. The overall abundance, number of species and biomass of netted fishes was higher around reefs. Rotenone collections of the more sedentary species showed a similar pattern, but suggested, however, that a simple reef versus surrounding sand and seagrass habitat comparison is complicated by the canopy-forming seagrass Amphibolis that occurs on reef tops. Time of day had an important effect on overall fish abundance and number of species, with peaks occurring at crepuscular periods. This reflected dusk and dawn activity peaks of a dominant species rather than overlapping activities of many diurnal and nocturnal species. Diel switches between reef-edge habitat and surrounding sand/seagrass flats were uncommon despite expectations (based on literature examples) that patch reefs would function primarily as sheltering habitats and surrounding non-reef areas act as foraging habitat. High catches at reef-edge sites suggest that the majority of fishes forage on or near limestone patch reefs. Fish densities of around 0.8 individuals per m^-2 of bottom on these Western Australian reefs are relatively high in comparison to visual census estimates obtained for temperate reef systems in South Australia and New Zealand, but similar to those obtained using comparable netting methods in temperate Australian seagrass systems.     

Temperature effects on anaesthesia with clove oil in six temperate‐zone fishes

The potential use of clove oil (eugenol) as an anaesthetic for Atlantic salmon Salmo salar , brown trout Salmo trutta , rainbow trout Oncorhynchus mykiss , whitefish Coregonus lavaretus , perch Perca fluviatilis and roach Rutilus rutilus was examined at 5, 10, 15 and 20° C using three anaesthetic concentrations (varying from 20 to 200 mg l⁻¹) at each temperature. Substantial species differences in sensitivity to clove oil were observed, even amongst congeners, and there may be some disadvantages (slow recovery and possibly mortality) with using clove oil for 0+ year whitefish and at low temperatures for perch and roach.     

Assessing the diversity and abundances of larvae and juveniles of coral reef fish: a synthesis of six sampling techniques

Due to an increasing emphasis for fish population survey and regulation, efficient tools for evaluating the abundance and diversity of fish from various life stages are needed, especially for coral reef species that present a high taxonomic diversity. The characteristics of six different techniques used for sampling pelagic larvae (a plankton-net and two light-traps), newly settled juveniles (one type of artificial reef), and older juveniles (an underwater seine net in seagrass and macroalgal beds, and rotenone poisoning in coral patches) are described in this study. Larvae belonging to 70 families and juveniles belonging to 34 families were collected. An analysis of similarity (ANOSIM) showed that the taxonomic composition of assemblages collected with the plankton-net and the two light-traps were overlapping but clearly different, due to the higher occurrence of Gobiidae in the plankton-net and of Pomacentridae in both light-traps. Larvae being 2–4 mm standard length (SL) dominated in the plankton-net, whereas larvae being 9–11 mm SL dominated in both light-traps. Pomacentridae juveniles were more abundant in rotenone samples, whereas Labridae dominated in the underwater seine. Juvenile fish collected with the artificial reefs, the underwater seine, and rotenone poisoning largely overlapped in size, with mean sizes of 22, 38, and 33 mm SL, respectively. Seven families were caught by the six sampling techniques, but with unequal success. This study provides ecologists and managers with a unique review of six techniques for sampling a wide range of developmental stages of young fish in different habitats of a coral reef lagoon.

Visual census methods underestimate density and diversity of cryptic reef fishes

The diversity and density of small, benthic reef fishes were estimated using visual census and enclosed rotenone stations. Visual census underestimated the number of species present and the density of common species by up to 91%.     

Effects of the fish anesthetic, clove oil (eugenol), on coral health and growth

Ecological research within coral reefs often requires the use of anesthetics to immobilize organisms. It is therefore important to consider the effect of these chemicals on the surrounding flora and fauna, particularly to the corals themselves. We quantified the effects of clove oil, a commonly used fish anesthetic, on the growth and occurrence of bleaching in three species of corals: Acropora striata, Pocillopora verrucosa, and Porites australiensis. We compared coral responses to five treatments: a gradient of four clove oil concentrations (0-28%) in seawater, and one concentration of clove oil (14%) in ethanol. Each week, we assessed the presence of bleaching, and then applied the treatment. We measured growth over the duration of the 6-week experiment using the buoyant weight technique. Growth and bleaching showed a dose response to clove oil exposure, and the use of ethanol as a solvent had an additional deleterious effect, as also suggested by observed changes in concentrations of eugenol following field application. Overall, growth was reduced by 37.6% at the highest concentration (28% clove oil in seawater) relative to the control (0% clove oil). The reduction in growth was nearly as great (35.3% of the control) at half the concentration of clove oil (14%) when dissolved in ethanol. These results suggest the repeated use of clove oil (even without a solvent) can deleteriously affect corals.     

Learned food aversion with and without an odour cue for protecting untreated baits from wild mammal foraging

Lethal methods of controlling wildlife foraging damage may present difficulties regarding conservation, ethics, welfare, and efficacy, providing an imperative to develop non-lethal alternatives. Learned food aversions offer a benign, targeted alternative to culling. However, food aversions are more readily associated with taste than with non-taste cues, and successful management applications have been limited primarily to reducing (bird) damage to treated items. To determine whether untreated foods might be protected without becoming damaged through sampling (tasting), we tested the role of an odour cue in learned food aversions with wild mammals using three conditioning treatments: (a) a combination of ziram (aversive agent) and clove oil (novel odour); (b) ziram; (c) clove oil. We tested two predictions: (1) ziram will produce learned aversion towards untreated foods; (2) training with the ziram–clove combination will produce enhanced aversion towards untreated foods in the presence of a clove odour cue. We collected detailed behavioural data from free-ranging animals using video surveillance. With European badgers Meles meles, both ziram treatments invoked innate aversion to baits. Ziram did not produce learned aversion to untreated foods, but conditioning badgers with the ziram–clove combination produced learned aversion towards untreated foods in the presence of the odour cue. The clove control did not affect badger behaviour. Our results support the second, but not the first, prediction with badgers. Red foxes Vulpes vulpes attended the ziram and the clove treatments only. Foxes displayed innate aversion to ziram, and subsequently developed learned aversions to untreated baits. Our results with foxes therefore support the first prediction, but we were unable to test the second. Learned food aversions using odour cues could potentially provide non-lethal protection for untreated foodstuffs, such as eggs, crops, and fruit, from mammalian pest species.     

Differential effects of anesthetics on electrical properties of the rainbow trout (Oncorhynchus mykiss) heart

We compared electrocardiographic signals in hatchery-reared, non-spinally-transected, immature rainbow trout (Oncorhynchus mykiss Walbaum) under clove oil (25 ppm), tricaine methanesulfonate (tricaine, 60 ppm), and benzocaine (108 ppm) general anesthesia (35 min, 14 degrees C). For all 3 anesthetics, the mean heart rate (HR) and QRS amplitude did not differ, and QRS duration and QT interval were independent of HR. Heart rate variability (HRV) was significantly (4-fold, P=0.032) higher under benzocaine than under clove oil and tricaine, but did not differ between clove oil and tricaine. QRS duration differed between groups (P<0.001, F=121); benzocaine anesthesia resulted in longer QRS complexes compared to clove oil (P<0.001) and tricaine (P<0.001) anesthesia, and QRS complexes under clove oil were longer than those under tricaine (P<0.001). High HRV and QRS amplitude variation with benzocaine were associated with HR oscillations as anesthetic exposure time increased, and suggest benzocaine toxicity which may influence cardiac function studies. Similar clove oil and tricaine ECG patterns suggest comparable autonomic effects, and maintenance of myocardial excitability. Given its low cost, ease of use, and similar ECG profiles to tricaine, clove oil is a viable alternative for studies of cardiac function in anesthetized rainbow trout.     

Complementarity of Rotating Video and Underwater Visual Census for Assessing Species Richness,Frequency and Density of Reef Fish on Coral Reef Slopes

Estimating diversity and abundance of fish species is fundamental for understanding community structure and dynamics of coral reefs. When designing a sampling protocol, one crucial step is the choice of the most suitable sampling technique which is a compromise between the questions addressed, the available means and the precision required. The objective of this study is to compare the ability to sample reef fish communities at the same locations using two techniques based on the same stationary point count method: one using Underwater Visual Census (UVC) and the other rotating video (STAVIRO). UVC and STAVIRO observations were carried out on the exact same 26 points on the reef slope of an intermediate reef and the associated inner barrier reefs. STAVIRO systems were always deployed 30 min to 1 hour after UVC and set exactly at the same place. Our study shows that; (i) fish community observations by UVC and STAVIRO differed significantly; (ii) species richness and density of large species were not significantly different between techniques; (iii) species richness and density of small species were higher for UVC; (iv) density of fished species was higher for STAVIRO and (v) only UVC detected significant differences in fish assemblage structure across reef type at the spatial scale studied. We recommend that the two techniques should be used in a complementary way to survey a large area within a short period of time. UVC may census reef fish within complex habitats or in very shallow areas such as reef flat whereas STAVIRO would enable carrying out a large number of stations focused on large and diver-averse species, particularly in the areas not covered by UVC due to time and depth constraints. This methodology would considerably increase the spatial coverage and replication level of fish monitoring surveys.     

Local ecological impacts of regional biodiversity on reef fish assemblages

Aim We examined comparative data for cryptobenthic reef fishes to determine how variation in regional species richness relates to local species richness, abundance, and taxonomic and trophic composition, and to test whether systems with higher species richness exhibit finer habitat partitioning. Locations Lizard Island, Great Barrier Reef (GBR), Australia; Bahía de Loreto, Gulf of California (GoC), Mexico. Methods Cryptobenthic reef fish assemblages from four habitats (coral heads, rubble, and horizontal and vertical surfaces of boulders) were collected using clove oil. Differences in density, species richness and biomass were examined between regions and among habitats. Habitat associations were identified for each habitat/location based on multivariate ordination, and the statistical significance of patterns was tested using analysis of similarity (ANOSIM). In addition, the trophic group composition of the assemblages for both regions was examined. Results A total of 91 species in 20 families were recorded (GBR, 66 species; GoC, 25 species). Total and habitat species richness were higher on the GBR, whereas biomass was higher in the GoC. No difference in fish density between regions was found. Habitat division among assemblages was greater in the depauperate GoC. Only coral head associations proved to be distinctive on the GBR, whereas three sample groups were found in the GoC (coral heads, horizontal boulders and vertical boulders/rubble). Trophic composition in the two regions was markedly different, with omnivores dominating the GBR fauna and planktivores the GoC. Main conclusions A positive regional–local relationship in fish diversity was found between regions, but fish abundance in both regions remained similar. Contrary to expectations, habitat partitioning, at a community level, was greater in the depauperate GoC. Differences in trophic composition and patterns of habitat use appear to reflect the disparate history of the regions, whereas patterns of abundance may reflect the influence of fundamental relationships between size and abundance in communities. This study highlights the potential of reef faunas to conform to universal numerical trends while maintaining an ability to respond ecologically to local/evolutionary influences. The GoC fauna appears to be exceptionally vulnerable to natural and anthropogenic disturbance owing to the high numerical dominance of habitat‐specific species and to the limited potential for functional redundancy within the system.     

Auditory sensitivity in settlement-stage larvae of coral reef fishes

The larval phase of most species of coral reef fishes is spent away from the reef in the pelagic environment. At the time of settlement, these larvae need to locate a reef, and recent research indicates that sound emanating from reefs may act as a cue to guide them. Here, the auditory abilities of settlement-stage larvae of four species of coral reef fishes (families Pomacentridae, Lutjanidae and Serranidae) and similar-sized individuals of two pelagic species (Carangidae) were tested using an electrophysiological technique, auditory brainstem response (ABR). Five of the six species heard frequencies in the 100–2,000 Hz range, whilst one carangid species did not detect frequencies higher than 800 Hz. The audiograms of the six species were of similar shape, with best hearing at lower frequencies between 100 and 300 Hz. Strong within-species differences were found in hearing sensitivity both among the coral reef species and among the pelagic species. Larvae of the coral reef species had significantly more sensitive hearing than the larvae of the pelagic species. The results suggest that settlement-stage larval reef fishes may be able to detect reef sounds at distances of a few 100 m. If true hearing thresholds are lower than ABR estimates, as indicated in some comparisons of ABR and behavioural methods, the detection distances would be much larger.     

Inhibition of quorum sensing regulated bacterial functions by plant essential oils with special reference to clove oil

Aims:  To evaluate quorum sensing (QS) inhibitory activity of plant essential oils using strains of Chromobacterium violaceum (CV12472 and CVO26) and Pseudomonas aeruginosa (PAO1).
Methods and Results:  Inhibition of QS-controlled violacein production in C. violaceum was assayed using disc diffusion and agar well diffusion method. Of the 21 essential oils, four oils showed varying levels of anti-QS activity. Syzygium aromaticum (Clove) oil showed promising anti-QS activity on both wild and mutant strains with zones of pigment inhibition 19 and 17 mm, respectively, followed by activity in cinnamon, lavender and peppermint oils. The effect of clove oil on the extent of violacein production was estimated photometrically and found to be concentration dependent. At sub-MICs of clove oil, 78·4% reduction in violacein production over control and up to 78% reduction in swarming motility in PAO1 over control were recorded. Gas chromatography–mass spectrometry analysis of clove oil indicated presence of many phytocompounds. Eugenol, the major constituent of clove oil could not exhibit anti-QS activity.
Conclusions:  Presence of anti-QS activity in clove oil and other essential oils has indicated new anti-infective activity. The identification of anti-QS phytoconstituents is needed to assess the mechanism of action against both C. violaceum and Ps. aeruginosa .
Significance and Impact of the study:  Essential oils having new antipathogenic drugs principle because of its anti-QS activity might be important in reducing virulence and pathogenicity of drug-resistant bacteria in vivo .     

An analysis of fish community responses to coral mining in the Maldives

Synopsis Coral mining takes place on shallow reef flats at a number of localities in the Maldives, but not on the adjacent deeper reef slopes. A semi-quantitative census method for fish species abundance and biomass is described. Fish community structure is compared on mined and non-mined reef flats and their adjacent slopes using a variety of univariate, graphical/distributional and multivariate statistical techniques. In general, univariate and graphical distributional methods do not indicate significant differences between mined and non-mined localities with respect to the relative abundances and biomasses of species. Multivariate methods (both classification and ordination), however, indicate very clear-cut effects of mining on the reef flats, and also significant effects on reef slopes adjacent to mined flats. The effect was equally clear using non-quantitative (presence/absence) data. The fish species mainly responsible for the differences between mined and non-mined localities are identified, and the differences are explained in terms of the feeding biology of these species.     

Comparative bioactivity of selected extracts from Meliaceae and some commercial botanical insecticides against two noctuid caterpillars, <Emphasis Type="Italic">Trichoplusia ni</Emphasis> and <Emphasis Type="Italic">Pseudaletia unipuncta</Emphasis>

Plant-derived extracts and phytochemicals have long been a subject of research in an effort to develop alternatives to conventional insecticides but with reduced health and environmental impacts. In this review we compare the bioactivities of some plant extracts with those of commercially available botanical insecticides against two important agricultural pests, the cabbage looper, Trichoplusia ni and the armyworm, Pseudaletia unipuncta. Test materials included extracts of Azadirachta indica (neem), A. excelsa (sentang), Melia volkensii, M. azedarach (Chinaberry) and Trichilia americana, (all belonging to the family Meliaceae) along with commercial botanical insecticides ryania, pyrethrum, rotenone and essential oils of rosemary and clove leaf. Most of the extracts and botanicals tested proved to be strong growth inhibitors, contact toxins and significant feeding deterrents to both lepidopteran species. However, there were interspecific differences with T. ni generally more susceptible to the botanicals than the armyworm, P. unipuncta. All botanicals were more inhibitory to growth and toxic (through feeding) to T. ni than to P. unipuncta, except for M. azedarach which was more toxic to P. unipuncta than to T. ni. Athough, pyrethrum was the most toxic botanical to both noctuids, A. indica, A. excelsa, and M. volkensii were more toxic than ryania, rotenone, clove oil and rosemary oil for T. ni. As feeding deterrents, pyrethrum was the most potent against T. ni, whereas A. indica was the most potent against the armyworm. Based upon growth inhibition, chronic toxicity, and antifeedant activity, some of these plant extracts have levels of activity that compare favorably to botanical products currently in commercial use and have potential for development as commercial insecticides.     

中草药精油对蜜蜂狄斯瓦螨的熏杀效果

在实验室条件下测定10种中草药精油对蜜蜂狄斯瓦螨Varroa destructor Anderson&Trueman的熏蒸效果,通过测定中草药精油对蜜蜂和螨的毒性,筛选出具有杀螨活性而对蜜蜂较安全的中草药精油。结果表明:中草药精油对蜜蜂都有一定的毒害;而在对蜜蜂无毒性的剂量下,48h时茴香油、丁香油、肉桂油分别能引起92.5%、54%和12%的螨死亡,显著高于对照组(P<0.05);根据初步筛选结果,选择茴香油和丁香油进行进一步毒力测定,结果表明48h时茴香油对螨的LD50为0.949μL,蜜蜂的LD50为4.033μL;丁香油对螨的LD50为0.795μL,蜜蜂的LD50为1.965μL。茴香油在48h时有着较高的选择比(蜜蜂的LD50/螨的LD50=4.250);GC-MS鉴定茴香油最主要成分是茴香脑(占总成分的88.72%),丁香油的主要成分是丁香酚(68.28%)和石竹烯(20.79%)。可见,茴香油和丁香油在控制狄斯瓦螨的应用上具有很大潜力。