Skin toxins and external parasitism of coral-dwelling gobies

Toxic (Gobiodon spp.) and non-toxic (Paragobiodon xanthosomus) gobies became infected with external parasites (gnathiid isopods) at equal rates in a laboratory experiment. Parasites were evenly distributed over the body of P. xanthosomus but were mostly confined to the fins of Gobiodon spp., where toxin glands are less abundant. Skin toxins were not associated with the rate of infection but their distribution did appear to influence the site of parasite attachment. (C) 2003 The Fisheries Society of the British Isles.

Visual Biology of Hawaiian Coral Reef Fishes. III. Environmental Light and an Integrated Approach to the Ecology of Reef Fish Vision

In the previous two papers in this three-part series, we have examined visual pigments, ocular media transmission, and colors of the coral reef fish of Hawaii. This paper first details aspects of the light field and background colors at the microhabitat level on Hawaiian reefs and does so from the perspective and scale of fish living on the reef. Second, information from all three papers is combined in an attempt to examine trends in the visual ecology of reef inhabitants. Our goal is to begin to see fish the way they appear to other fish. Observations resulting from the combination of results in all three papers include the following. Yellow and blue colors on their own are strikingly well matched to backgrounds on the reef such as coral and bodies of horizontally viewed water. These colors, therefore, depending on context, may be important in camouflage as well as conspicuousness. The spectral characteristics of fish colors are correlated to the known spectral sensitivities in reef fish single cones and are tuned for maximum signal reliability when viewed against known backgrounds. The optimal positions of spectral sensitivity in a modeled dichromatic visual system are generally close to the sensitivities known for reef fish. Models also predict that both UV-sensitive and red-sensitive cone types are advantageous for a variety of tasks. UV-sensitive cones are known in some reef fish, red-sensitive cones have yet to be found. Labroid colors, which appear green or blue to us, may he matched to the far-red component of chlorophyll reflectance for camouflage. Red cave/hole dwelling reef fish are relatively poorly matched to the background they are often viewed against but this may be visually irrelevant. The model predicts that the task of distinguishing green algae from coral is optimized with a relatively long wavelength visual pigment pair. Herbivorous grazers whose visual pigments are known possess the longest sensitivities so far found. Labroid complex colors are highly contrasting complementary colors close up but combine, because of the spatial addition, which results from low visual resolution, at distance, to match background water colors remarkably well. Therefore, they are effective for simultaneous communication and camouflage.

Visual biology of Hawaiian coral reef fishes. II. Colors of Hawaiian coral reef fish

The colors of 51 species of Hawaiian reef fish have been measured using a spectrometer and therefore can be described in objective terms that are not influenced by the human visual experience. In common with other known reef fish populations, the colors of Hawaiian reef fish occupy spectral positions from 300-800nm; yellow or orange with blue, yellow with black, and black with white are the most frequently combined colors; and there is no link between possession of ultraviolet (UV) reflectance and UV visual sensitivity or the potential for UV visual sensitivity. In contrast to other reef systems, blue, yellow, and orange appear more frequently in Hawaiian reef fish. Based on spectral quality of reflections from fish skin, trends in fish colors can be seen that are indicative of both visually driven selective pressures and chemical or physical constraints on the design of colors. UV-reflecting colors can function as semiprivate communication signals. White or yellow with black form highly contrasting patterns that transmit well through clear water. Labroid fishes display uniquely complex colors but lack the ability to see the UV component that is common in their pigments. Step-shaped spectral curves are usually long-wavelength colors such as yellow or red, and colors with a peak-shaped spectral curves are green, blue, violet, and UV.

Lecithophyllum kitrii n. sp (Digenea : Lecithasteridae) from Australian coral reef fishes of the genus Siganus

Lecithophyllum kitrii n. sp. is described from Siganus punctatus and S. lineatus off Heron Island on the southern Great Barrier Reef, Australia. It differs from most other species in the genus in its elongate pars prostatica and globular sinus-sac, and from all other species in having the seminal vesicle almost always entirely in the hindbody.

Identical digeneans in coral reef fishes from French Polynesia and the Great Barrier Reef (Australia) demonstrated by morphology and molecules

Three coral reef fish species, Zanclus cornutus, Chaetodon vagabundus and Naso lituratus, were collected in French Polynesia and on the Great Barrier Reef, Queensland. These fish species were each infected by one morphologically similar digenean species in both localities; Schistorchis Zancli Hanson, 1953 was found in Zanclus cornutus. Preptetos laguncula Bray and Cribb, 1996 in Naso lituratus and Neohypocreadium dorsoporum Machida and Uchida, 1987 in Chaetodon vagabundus. In addition, on the Great Barrier Reef P. laguncula was also found in Naso unicornis and N. dorsoporum in Chaetodon ephippium and Chaetodon flavirostris. Morphometric differences between the species from the two sites were only slight. Sequences from the second internal transcribed spacer of the ribosomal DNA of each worm revealed total homology or negligible divergence between samples from hosts caught in French Polynesia and on the Great Barrier Reef. These results show that across more than 6000 km these digeneans are similar in morphology and genotype. Some species of fishes and molluscs a-re considered to have distributions that encompass the entire tropical Indo-West Pacific. These findings suggest that at least some of their parasites have similarly broad distributions. (C) 2001 Australian Society for Parasitology Inc. Published by Elsevier Science Ltd. All rights reserved.

Visual Biology of Hawaiian Coral Reef Fishes. I. Ocular Transmission and Visual Pigments

The visual biology of Hawaiian reef fishes was explored by examining their eyes for spectral sensitivity of their visual pigments and for transmission of light through the ocular media to the retina. The spectral absorption curves for the visual pigments of 38 species of Hawaiian fish were recorded using microspectrophotometry. The peak absorption wavelength (lambda(max)) of the rods varied from 477-502 nm and the lambda(max) of individual species conformed closely to values for the same species previously reported using a whole retina extraction procedure. The visual pigments of single cone photoreceptors were categorized, dependent on their lambda(max)-values, as ultraviolet (347-376 nm), violet (398-431 nm) or blue (439-498 nm) sensitive cones. Eight species possessed ultraviolet-sensitive cones and 14 species violet-sensitive cones. Thus, 47% of the species examined displayed photosensitivity to the short-wavelength region of the spectrum. Both identical and nonidentical paired and double cones were found with blue sensitivity or green absorption peaks (> 500 nm). Spectrophotometry of the lens, cornea, and humors for 195 species from 49 families found that the spectral composition of the light transmitted to the retina was most often limited by the lens (73% of species examined). Except for two unusual species with humor-limited eyes, Acanthocybium solandri (Scombridae) and the priacanthid fish, Heteropriacanthus cruentatus, the remainder had corneal-limited eyes. The wavelength at which 50% of the light was blocked (T50) was classified according to a system modified from Douglas and McGuigan (1989) as Type I, T50 < = 355 nm, (32 species); Type IIa, 355 < T50 < = 380 nm (30 species); Type IIb, 380 < T50 405 nm (84 species). Possession of UV-transmitting ocular media follows both taxonomic and functional lines and, if the ecology of the species is considered, is correlated with the short-wavelength visual pigments found in the species. Three types of short-wavelength vision in fishes are hypothesized: UV-sensitive, UV-specialized, and violet-specialized. UV-sensitive eyes lack UV blockers (Type I and IIa) and can sense UV light with the secondary absorption peak or beta peak of their longer wavelength visual pigments but do not possess specialized UV receptor cells and, therefore, probably lack UV hue discrimination. UV-specialized eyes allow transmission of UV light to the retina (Type I and IIa) and also possess UV-sensitive cone receptors with peak absorption between 300 and 400 nm. Given the appropriate perceptual mechanisms, these species could possess true UV-color vision and hue discrimination. Violet-specialized eyes extend into Type IIb eyes and possess violet-sensitive cone cells. UV-sensitive eyes are found throughout the fishes from at least two species of sharks to modern bony fishes. Eyes with specialized short-wavelength sensitivity are common in tropical reef fishes and must be taken into consideration when performing research involving the visual perception systems of these fishes. Because most glass and plastics are UV-opaque, great care must be taken to ensure that aquarium dividers, specimen holding containers, etc., are UV-transparent or at least to report the types of materials in use.

Seawater carbonate chemistry and aerobic performance of coral reef fishes during experiments, 2009

Concerns about the impacts of ocean acidification on marine life have mostly focused on how reduced carbonate saturation affects calcifying organisms. Here, we show that levels of CO2-induced acidification that may be attained by 2100 could also have significant effects on marine organisms by reducing their aerobic capacity. The effects of temperature and acidification on oxygen consumption were tested in 2 species of coral reef fishes, Ostorhinchus doederleini and O. cyanosoma, from the Great Barrier Reef, Australia. The capacity for aerobic activity (aerobic scope) declined at temperatures above the summer average (29°C) and in CO2-acidified water (pH 7.8 and ~1000 ppm CO2) compared to control water (pH 8.15). Aerobic scope declined by 36 and 32% for O. doederleini and O. cyanosoma at temperatures between 29 to 32°C, whereas it declined by 33 and 47% for O. doederleini and O. cyanosoma in acidified water compared to control water. Thus, the declines in aerobic scope in acidified water were similar to those caused by a 3°C increase in water temperature. Minimum aerobic scope values of ~200 mg O2 kg-1 h-1 were attained for both species in acidified water at 32°C, compared with over 600 mg O2 kg-1 h-1 in control water at 29°C. Mortality rate increased sharply at 33°C, indicating that this temperature is close to the lethal thermal limit for both species. Acidification further increased the mortality rate of O. doederleini, but not of O. cyanosoma. These results show that coral reef fishes are sensitive to both higher temperatures and increased levels of dissolved CO2, and that the aerobic performance of some reef fishes could be significantly reduced if climate change continues unabated.

Effects of ocean acidification on visual risk assessment in coral reef fishes

1. With the global increase in CO2 emissions, there is a pressing need for studies aimed at understanding the effects of ocean acidification on marine ecosystems. Several studies have reported that exposure to CO2 impairs chemosensory responses of juvenile coral reef fishes to predators. Moreover, one recent study pointed to impaired responses of reef fish to auditory cues that indicate risky locations. These studies suggest that altered behaviour following exposure to elevated CO2 is caused by a systemic effect at the neural level. 2. The goal of our experiment was to test whether juvenile damselfish Pomacentrus amboinensis exposed to different levels of CO2 would respond differently to a potential threat, the sight of a large novel coral reef fish, a spiny chromis, Acanthochromis polyancanthus, placed in a watertight bag. 3. Juvenile damselfish exposed to 440 (current day control), 550 or 700 µatm CO2 did not differ in their response to the chromis. However, fish exposed to 850 µatm showed reduced antipredator responses; they failed to show the same reduction in foraging, activity and area use in response to the chromis. Moreover, they moved closer to the chromis and lacked any bobbing behaviour typically displayed by juvenile damselfishes in threatening situations. 4. Our results are the first to suggest that response to visual cues of risk may be impaired by CO2 and provide strong evidence that the multi-sensory effects of CO2 may stem from systematic effects at the neural level.

Effects of ocean acidification on learning in coral reef fishes

Ocean acidification has the potential to cause dramatic changes in marine ecosystems. Larval damselfish exposed to concentrations of CO2 predicted to occur in the mid- to late-century show maladaptive responses to predator cues. However, there is considerable variation both within and between species in CO2 effects, whereby some individuals are unaffected at particular CO2 concentrations while others show maladaptive responses to predator odour. Our goal was to test whether learning via chemical or visual information would be impaired by ocean acidification and ultimately, whether learning can mitigate the effects of ocean acidification by restoring the appropriate responses of prey to predators. Using two highly efficient and widespread mechanisms for predator learning, we compared the behaviour of pre-settlement damselfish Pomacentrus amboinensis that were exposed to 440 µatm CO2 (current day levels) or 850 µatm CO2, a concentration predicted to occur in the ocean before the end of this century. We found that, regardless of the method of learning, damselfish exposed to elevated CO2 failed to learn to respond appropriately to a common predator, the dottyback, Pseudochromis fuscus. To determine whether the lack of response was due to a failure in learning or rather a short-term shift in trade-offs preventing the fish from displaying overt antipredator responses, we conditioned 440 or 700 µatm-CO2 fish to learn to recognize a dottyback as a predator using injured conspecific cues, as in Experiment 1. When tested one day post-conditioning, CO2 exposed fish failed to respond to predator odour. When tested 5 days post-conditioning, CO2 exposed fish still failed to show an antipredator response to the dottyback odour, despite the fact that both control and CO2-treated fish responded to a general risk cue (injured conspecific cues). These results indicate that exposure to CO2 may alter the cognitive ability of juvenile fish and render learning ineffective.

The stability of P in coral reef fishes

The constancy of phenotypic variation and covariation is an assumption that underlies most recent investigations of past selective regimes and attempts to predict future responses to selection. Few studies have tested this assumption of constancy despite good reasons to expect that the pattern of phenotypic variation and covariation may vary in space and time. We compared phenotypic variance-covariance matrices (P) estimated for Populations of six species of distantly related coral reef fishes sampled at two locations on Australia's Great Barrier Reef separated by more than 1000 km. The intraspecific similarity between these matrices was estimated using two methods: matrix correlation and common principal component analysis. Although there was no evidence of equality between pairs of P, both statistical approaches indicated a high degree of similarity in morphology between the two populations for each species. In general, the hierarchical decomposition of the variance-covariance structure of these populations indicated that all principal components of phenotypic variance-covariance were shared but that they differed in the degree of variation associated with each of these components. The consistency of this pattern is remarkable given the diversity of morphologies and life histories encompassed by these species. Although some phenotypic instability was indicated, these results were consistent with a generally conserved pattern of multivariate selection between populations.

Spatial behavior of two coral reef fishes within a Caribbean Marine Protected Area

A better understanding of the key ecological processes of marine organisms is fundamental to improving design and effective implementation of marine protected areas (MPAs) and marine biodiversity. The movement behavior of coral reef fish is a complex mechanism that is highly linked to species life-history traits, predation risk and food resources. We used passive acoustic telemetry to study monthly, daily and hourly movement patterns and space use in two species, Schoolmaster snapper (Lutjanus apodus) and Stoplight parrotfish (Sparisoma viride). We investigated the spatial overlap between the two species and compared intra-specific spatial overlap between day and night. Presence-absence models showed different diel presence and habitat use patterns between the two species. We constructed a spatial network of the movement patterns, which showed that for both species when fish were detected by the array of receivers most movements were made around the coral reef habitat while occasionally moving to silt habitats. Our results show that most individuals made predictable daily crepuscular migrations between different locations and habitat types, although individual behavioral changes were observed for some individuals across time. Our study also highlights the necessity to consider multiple species during MPA implementation and to take into account the specific biological and ecological traits of each species. The low number of fish detected within the receiver array, as well as the intraspecific variability observed in this study, highlight the need to compare results across species and individuals to be used for MPA management.

Evidence for sympatric speciation by host shift in the sea

The genetic divergence and evolution of new species within the geographic range of a single population (sympatric speciation) contrasts with the well-established doctrine that speciation occurs when populations become geographically isolated (allopatric speciation). Although there is considerable theoretical support for sympatric speciation [1, 2], this mode of diversification remains controversial, at least in part because there are few well-supported examples [3]. We use a combination of molecular, ecological, and biogeographical data to build a case for sympatric speciation by host shift in a new species of coral-dwelling fish (genus Gobiodon). We propose that competition for preferred coral habitats drives host shifts in Gobiodon and that the high diversity of corals provides the source of novel, unoccupied habitats. Disruptive selection in conjunction with strong host fidelity could promote rapid reproductive isolation and ultimately lead to species divergence. Our hypothesis is analogous to sympatric speciation by host shift in phytophagous insects [4, 5] except that we propose a primary role for intraspecific competition in the process of speciation. The fundamental similarity between these fishes and insects is a specialized and intimate relationship with their hosts that makes them ideal candidates for speciation by host shift.

Diurnal temporal patterns of the diversity and the abundance of reef fishes in a branching coral patch in New Caledonia

Small-scale spatial and temporal variability in animal abundance is an intrinsic characteristic of marine ecosystems but remains largely unknown for most animals, including coral reef fishes. In this study, we used a remote autonomous unbaited video system and recorded reef fish assemblages during daylight hours, 10 times a day for 34 consecutive days in a branching coral patch of the lagoon of New Caledonia. In total, 50 031 fish observations belonging to 114 taxa, 66 genera and 31 families were recorded in 256 recorded videos. Carnivores and herbivore-detritus feeders dominated the trophic structure. We found significant variations in the composition of fish assemblages between times of day. Taxa richness and fish abundance were greater in the early morning and in the late afternoon than during the day. Fourteen taxa displayed well-defined temporal patterns in abundance with one taxon influenced by time of day, six influenced by tidal state and seven influenced by both time of day and tidal state. None of these 14 taxa were piscivores, 10 were herbivore-detritus feeders, three were carnivores and one was plankton feeder. Our results suggest a diel migration from feeding grounds to shelter areas and highlight the importance of taking into account small-scale temporal variability in animal diversity and abundance when studying connectivity between habitats and monitoring communities.