Full-Sibs in Cohorts of Newly Settled Coral Reef Fishes

Reef fishes exhibit a bipartite life cycle where a benthic adult stage is preceded by a pelagic dispersal phase during which larvae are presumed to be mixed and transported by oceanic currents. Genetic analyses based on twelve microsatellite loci of 181 three-spot dascyllus (Dascyllus trimaculatus) that settled concurrently on a small reef in French Polynesia revealed 11 groups of siblings (1 full sibs and 10 half-sibs). This is the first evidence that fish siblings can journey together throughout their entire planktonic dispersal phase (nearly a month long for three-spot dascyllus). Our findings have critical implications for the dynamics and genetic structure of fish populations, as well as for the design of marine protected areas and management of fisheries.     

Counter-Gradient Variation in Respiratory Performance of Coral Reef Fishes at Elevated Temperatures

The response of species to global warming depends on how different populations are affected by increasing temperature throughout the species'' geographic range. Local adaptation to thermal gradients could cause populations in different parts of the range to respond differently. In aquatic systems, keeping pace with increased oxygen demand is the key parameter affecting species'' response to higher temperatures. Therefore, respiratory performance is expected to vary between populations at different latitudes because they experience different thermal environments. We tested for geographical variation in respiratory performance of tropical marine fishes by comparing thermal effects on resting and maximum rates of oxygen uptake for six species of coral reef fish at two locations on the Great Barrier Reef (GBR), Australia. The two locations, Heron Island and Lizard Island, are separated by approximately 1200 km along a latitudinal gradient. We found strong counter-gradient variation in aerobic scope between locations in four species from two families (Pomacentridae and Apogonidae). High-latitude populations (Heron Island, southern GBR) performed significantly better than low-latitude populations (Lizard Island, northern GBR) at temperatures up to 5°C above average summer surface-water temperature. The other two species showed no difference in aerobic scope between locations. Latitudinal variation in aerobic scope was primarily driven by up to 80% higher maximum rates of oxygen uptake in the higher latitude populations. Our findings suggest that compensatory mechanisms in high-latitude populations enhance their performance at extreme temperatures, and consequently, that high-latitude populations of reef fishes will be less impacted by ocean warming than will low-latitude populations.     

Monitoring Herbivorous Fishes as Indicators of Coral Reef Resilience in American Samoa

Resilience-based management aims to promote or protect processes and species that underpin an ecosystem''s capacity to withstand and recover from disturbance. The management of ecological processes is a developing field that requires reliable indicators that can be monitored over time. Herbivory is a key ecological process on coral reefs, and pooling herbivorous fishes into functional groups based on their feeding mode is increasingly used as it may quantify herbivory in ways that indicate resilience. Here we evaluate whether the biomass estimates of these herbivore functional groups are good predictors of reef benthic assemblages, using data from 240 sites from five island groups in American Samoa. Using an information theoretic approach, we assembled a candidate set of linear and nonlinear models to identify the relations between benthic cover and total herbivore and non-herbivore biomass and the biomass of the aforementioned functional groups. For each benthic substrate type considered (encrusting algae, fleshy macroalgae, hard coral and turf algae), the biomass of herbivorous fishes were important explanatory variables in predicting benthic cover, whereas biomass of all fishes combined generally was not. Also, in all four cases, variation in cover was best explained by the biomass of specific functional groups rather than by all herbivores combined. Specifically: 1) macroalgal and turf algal cover decreased with increasing biomass of ‘grazers/detritivores’; and 2) cover of encrusting algae increased with increasing biomass of ‘grazers/detritivores’ and browsers. Furthermore, hard coral cover increased with the biomass of large excavators/bio-eroders (made up of large-bodied parrotfishes). Collectively, these findings emphasize the link between herbivorous fishes and the benthic community and demonstrate support for the use of functional groups of herbivores as indicators for resilience-based monitoring.     

Reef Fishes in Biodiversity Hotspots Are at Greatest Risk from Loss of Coral Species

Coral reef ecosystems are under a variety of threats from global change and anthropogenic disturbances that are reducing the number and type of coral species on reefs. Coral reefs support upwards of one third of all marine species of fish, so the loss of coral habitat may have substantial consequences to local fish diversity. We posit that the effects of habitat degradation will be most severe in coral regions with highest biodiversity of fishes due to greater specialization by fishes for particular coral habitats. Our novel approach to this important but untested hypothesis was to conduct the same field experiment at three geographic locations across the Indo-Pacific biodiversity gradient (Papua New Guinea; Great Barrier Reef, Australia; French Polynesia). Specifically, we experimentally explored whether the response of local fish communities to identical changes in diversity of habitat-providing corals was independent of the size of the regional species pool of fishes. We found that the proportional reduction (sensitivity) in fish biodiversity to loss of coral diversity was greater for regions with larger background species pools, reflecting variation in the degree of habitat specialization of fishes across the Indo-Pacific diversity gradient. This result implies that habitat-associated fish in diversity hotspots are at greater risk of local extinction to a given loss of habitat diversity compared to regions with lower species richness. This mechanism, related to the positive relationship between habitat specialization and regional biodiversity, and the elevated extinction risk this poses for biodiversity hotspots, may apply to species in other types of ecosystems.     

Body Fineness Ratio as a Predictor of Maximum Prolonged-Swimming Speed in Coral Reef Fishes

The ability to sustain high swimming speeds is believed to be an important factor affecting resource acquisition in fishes. While we have gained insights into how fin morphology and motion influences swimming performance in coral reef fishes, the role of other traits, such as body shape, remains poorly understood. We explore the ability of two mechanistic models of the causal relationship between body fineness ratio and endurance swimming-performance to predict maximum prolonged-swimming speed (U_max) among 84 fish species from the Great Barrier Reef, Australia. A drag model, based on semi-empirical data on the drag of rigid, submerged bodies of revolution, was applied to species that employ pectoral-fin propulsion with a rigid body at U_max. An alternative model, based on the results of computer simulations of optimal shape in self-propelled undulating bodies, was applied to the species that swim by body-caudal-fin propulsion at U_max. For pectoral-fin swimmers, U_max increased with fineness, and the rate of increase decreased with fineness, as predicted by the drag model. While the mechanistic and statistical models of the relationship between fineness and U_max were very similar, the mechanistic (and statistical) model explained only a small fraction of the variance in U_max. For body-caudal-fin swimmers, we found a non-linear relationship between fineness and U_max, which was largely negative over most of the range of fineness. This pattern fails to support either predictions from the computational models or standard functional interpretations of body shape variation in fishes. Our results suggest that the widespread hypothesis that a more optimal fineness increases endurance-swimming performance via reduced drag should be limited to fishes that swim with rigid bodies.     

Population Dynamics and Spatial Distribution of Coral Reef Fishes: Comparison Between Continuous and Isolated Habitats

Recent studies have shown that there are high degrees of spatial and temporal stability in coral reef fish assemblage structures in a continuous habitat, in contrast to results of observations in isolated habitats. In order to determine the reason for the difference in temporal stability of fish assemblage structures in a continuous habitat site and an isolated habitat site, population dynamics and spatial distributions of coral reef fishes (six species of pomacentrids and two species of apogonids) in the two habitat site were investigated over a 2-year period in an Okinawan coral reef. The population densities of pomacentrid and apogonid species increased in juvenile settlement periods at both sites, but the magnitude of seasonal fluctuation in population density was significantly greater at the isolated habitat site, indicating that the rate of juvenile settlement and mortality rate in the isolated habitat were greater than those in the continuous habitat. The magnitude of aggregation of fishes, which affects density-dependent biological interactions that modify population density such as competition and predation, was also significantly greater at the isolated habitat site, especially in the juvenile settlement season. Most of the fishes at the isolated habitat site exhibited more generalized patterns of microhabitat selection because of less coral coverage and diversity. The seasonal stability in the species composition of fishes was greater at the continuous habitat site than that at the isolated habitat. Our findings suggest that the relative importance of various ecological factors responsible for regulation of the population density of coral reef fishes (e.g., competition, predation, microhabitat selection and post-settlement movement) in a continuous habitat site and the isolated habitat site are different.     

Sporadic Disturbances in Fluctuating Coral Reef Environments: El Nino and Coral Reef Development in the Eastern Pacific

The disastrous effects of the intense 1982–83 El Niño-SouthernOscillation (ENSO) bring new insight into the long-term developmentof eastern Pacific coral reefs. The 1988–83 ENSO sea surfacewarming event caused extensive reef coral bleaching (loss ofsymbiotic zooxanthellae), resulting in up to 70–95% coralmortality on reefs in Costa Rica, Panama, Colombia and Ecuador.In the Galapagos Islands (Ecuador), most coral reefs experienced>95% coral mortality. Also, several coral species experiencedextreme reductions in population size, and local and regionalextinctions. The El Niño event spawned secondary disturbances,such as increased predation and bioerosion, that continue toimpact reef-building corals. The death of Pocillopora colonieswith their crustacean guards eliminated coral barriers now allowingthe corallivore Acanthaster planci access to formerly protectedcoral prey. Sea urchins and other organisms eroded disturbedcorals at rates that exceed carbonate production, potentiallyresulting in the elimination of existing reef buildups. In otherreefbuilding regions following extensive, catastrophic coralmortality, rapid recovery often occurs through the growth ofsurviving corals, recruitment of new corals from nearby sourcepopulations, and survival of consolidated reef surfaces. Inthe eastern Pacific, however, the return of upwelling conditionsand the survival of coral predators and bioeroders hamper coralreef recovery by reducing recruitment success and eroding coralreef substrates. Thus, coral reef growth that occurs betweendisturbance events is not conserved. Repeated El Niñodisturbances, which have occurred throughout the recent geologichistory of the eastern Pacific, prevent coral communities fromincreasing in diversity and limit the development and persistenceof significant reef features. The poor development of easternPacific coral reefs throughout Holocene and perhaps much ofPleistocene time may result from recurrent thermal disturbancesof the intensity of the 1982–83 El Niño event.     

Patterns of Embryo Mortality in a Demersally Spawning Coral Reef Fish and the Role of Predatory Fishes

The biological significance of embryo mortality in demersally spawning coral reef fishes is poorly understood. Here we describe patterns of variation in embryo mortality in Pomacentrus amboinensis (Pomacentridae) at Lizard Island (Great Barrier Reef). The aim was to determine whether numbers of embryos hatched substantially differed from egg production, and if so, identify whether predatory fishes were a source of embryo mortality. Spawning success (number of eggs laid), embryo mortality (proportion of embryos that died prior to hatching) and number of embryos hatching were estimated from daily maps of clutches laid on artificial surfaces (PVC tiles) defended by nesting males. Patterns of variation in eggs laid, embryo mortality and numbers of embryos hatched were examined at three spatial scales: (1) among widely-spaced locations around the island; (2) between adjacent reef slope and patch reef habitats occupied by P. amboinensis at a single location; and (3) among different males within these two habitats. The embryo mortality was extremely high, with a mean of 25.9pm ± 6.2% (S.E.) for 4 locations examined in 1994 and a mean of 69.2pm ± 2.9% for two habitats surveyed in 1995. There were no significant differences in embryo mortality among locations or habitats in either year. This meant that spatial patterns in the number of embryos hatching reflected differences in the number of eggs laid on tiles. Embryo mortality was extremely variable on the scale of individual territories, with embryo mortality commonly ranging from 0% to 100%. Much of the mortality could be attributed to diurnal predatory fishes, especially the wrasse Thalassoma lunare. However, variation in predator densities did not explain spatial patterns in embryo mortality rates. Both solitary and group predatory behaviour was observed, with groups often causing 100% embryo mortality. The level of embryo mortality observed suggests that predation prior to hatching may have a substantial effect on the reproductive output of populations of this demersal-nesting fish.     

Out-migration of Tagged Fishes from Marine Reef National Parks to Fisheries in Coastal Kenya

We evaluated movements of 25 species of coral reef fishes from Malindi and Watamu Marine National Parks (created 1968) in coastal Kenya from February 2001 to March 2002. Only three species, the commercially important whitespotted rabbitfish, Siganus sutor, the sky emperor (SEM), Lethrinus mahsena and the trumpet emperor, L. miniatus, exhibited consistent movements from the parks. At Malindi Park, more fishes were recaptured by fishermen off a fringing reef than off a patch reef. The rabbitfish had a higher monthly spillover rate from the fringing reef than from the patch reef. In contrast, the SEM had low monthly spillover rates from both reefs. The rabbitfish moved greater distances off the fringing reef than off the patch reef. At Watamu Park, the SEM, L. miniatus and the gold-spotted sweetlips, Gaterin flavomaculatus, had equal monthly spillover rates. In contrast, the rabbitfish had a lower monthly rate. The emperors showed no difference in net distance moved from the park boundary, however, L. miniatus traveled significantly longer distances than did the SEM. Distances between release and capture sites were either random (SEM), increasing (L. miniatus), or decreasing (rabbitfish) with respect to time at liberty.     

Diversity among Macroalgae-Consuming Fishes on Coral Reefs: A Transcontinental Comparison

Despite high diversity and abundance of nominally herbivorous fishes on coral reefs, recent studies indicate that only a small subset of taxa are capable of removing dominant macroalgae once these become established. This limited functional redundancy highlights the potential vulnerability of coral reefs to disturbance and stresses the need to assess the functional role of individual species of herbivores. However, our knowledge of species-specific patterns in macroalgal consumption is limited geographically, and there is a need to determine the extent to which patterns observed in specific reefs can be generalised at larger spatial scales. In this study, video cameras were used to quantify rates of macroalgae consumption by fishes in two coral reefs located at a similar latitude in opposite sides of Australia: the Keppel Islands in the Great Barrier Reef (eastern coast) and Ningaloo Reef (western coast). The community of nominally herbivorous fish was also characterised in both systems to determine whether potential differences in the species observed feeding on macroalgae were related to spatial dissimilarities in herbivore community composition. The total number of species observed biting on the dominant brown alga Sargassum myriocystum differed dramatically among the two systems, with 23 species feeding in Ningaloo, compared with just 8 in the Keppel Islands. Strong differences were also found in the species composition and total biomass of nominally herbivorous fish, which was an order of magnitude higher in Ningaloo. However, despite such marked differences in the diversity, biomass, and community composition of resident herbivorous fishes, Sargassum consumption was dominated by only four species in both systems, with Naso unicornis and Kyphosus vaigiensis consistently emerging as dominant feeders of macroalgae.     

Influence of Coral Reef Rugosity on Fish Communities in Marine Reserves Around Lombok Island,Indonesia

Environmental Biology of Fishes - Coral reef structural form is widely considered a key factor with respect to the availability of shelter and foraging spaces for fishes and invertebrates. However,...     

Global Biogeography of Reef Fishes: A Hierarchical Quantitative Delineation of Regions

Delineating regions is an important first step in understanding the evolution and biogeography of faunas. However, quantitative approaches are often limited at a global scale, particularly in the marine realm. Reef fishes are the most diversified group of marine fishes, and compared to most other phyla, their taxonomy and geographical distributions are relatively well known. Based on 169 checklists spread across all tropical oceans, the present work aims to quantitatively delineate biogeographical entities for reef fishes at a global scale. Four different classifications were used to account for uncertainty related to species identification and the quality of checklists. The four classifications delivered converging results, with biogeographical entities that can be hierarchically delineated into realms, regions and provinces. All classifications indicated that the Indo-Pacific has a weak internal structure, with a high similarity from east to west. In contrast, the Atlantic and the Eastern Tropical Pacific were more strongly structured, which may be related to the higher levels of endemism in these two realms. The “Coral Triangle”, an area of the Indo-Pacific which contains the highest species diversity for reef fishes, was not clearly delineated by its species composition. Our results show a global concordance with recent works based upon endemism, environmental factors, expert knowledge, or their combination. Our quantitative delineation of biogeographical entities, however, tests the robustness of the results and yields easily replicated patterns. The similarity between our results and those from other phyla, such as corals, suggests that our approach may be of broad utility in describing and understanding global marine biodiversity patterns.     

Morphology of the eye and visual acuities in the settlement-intervals of some Coral Reef Fishes (Labridae, Scaridae)

The morphology of the retina and photoreceptors of settlement-interval larvae and early juveniles and some adults of 12 species of Caribbean labrids and scarids were examined using histological techniques. The retinal structure is described in these species and life intervals. Larvae have a pure cone retina and unorganized mosaic and organization into a square mosaic pattern occurs during metamorphosis. Early post-settlement juveniles have an organized mosaic with structures that may enable them to detect polarized and UV light. Visual acuities were calculated for all species and life intervals and acuities ranged between 86.6–29.4min of arc in the settlement-intervals and 16–1.8min of arc in the adults. The visual abilities of the settlement-interval fishes and the possibility of the use of vision during settlement are discussed.     

Effects of Habitat Connectivity on the Abundance and Species Richness of Coral Reef Fishes: Comparison of an Experimental Habitat Established at a Rocky Reef Flat and at a Sandy Sea Bottom

Coral reef fish assemblages are widely recognized for the coexistence of numerous species, which are likely governed by both coral diversity and substratum complexity. However, since coral reefs provide diverse habitats due to their physical structure and different spatial arrangements of coral, findings obtained from an isolated habitat cannot necessarily be applied to fish assemblages in other habitats (e.g. continuous habitats). The aim of this study, therefore, was to determine by a field experiment whether habitat connectivity (spatial arrangement of coral colonies) affects abundance and species richness of fishes in an Okinawan coral reef. The experiment consisted of transplanted branching coral colonies at a 4m×8m quadrat at both a rocky reef flat and sandy sea bottom. Generally, the abundance of fishes was greater at the sandy sea bottom, especially for three species of pomacentrids, one species of labrids, one species of chaetodontids and two species of apogonids. Species–area curves showed that the species richness of fishes was significantly greater in the quadrat at the sandy sea bottom at 3, 6 and 9 months after the start of the experiment. The rate of increase in abundance of fishes per area was significantly greater in the quadrat at the sandy sea bottom over the study period. The results of rarefaction analyses showed that the rate of increase in species richness per abundance was significantly higher in the quadrat at the sandy sea bottom in the juvenile settlement period, indicating that the magnitude of dominance by particular species was greater at the sandy sea bottom habitat. Our findings suggest that habitat connectivity affects the abundance and species richness of coral reef fishes, i.e. the isolated habitat was significantly more attractive for fishes than was the continuous habitat. Our findings also suggest that the main ecological factors responsible for organization of fish assemblage at a continuous habitat and at an isolated habitat are different.     

A Morphospace for Reef Fishes: Elongation Is the Dominant Axis of Body Shape Evolution

Tropical reef fishes are widely regarded as being perhaps the most morphologically diverse vertebrate assemblage on earth, yet much remains to be discovered about the scope and patterns of this diversity. We created a morphospace of 2,939 species spanning 56 families of tropical Indo-Pacific reef fishes and established the primary axes of body shape variation, the phylogenetic consistency of these patterns, and whether dominant patterns of shape change can be accomplished by diverse underlying changes. Principal component analysis showed a major axis of shape variation that contrasts deep-bodied species with slender, elongate forms. Furthermore, using custom methods to compare the elongation vector (axis that maximizes elongation deformation) and the main vector of shape variation (first principal component) for each family in the morphospace, we showed that two thirds of the families diversify along an axis of body elongation. Finally, a comparative analysis using a principal coordinate analysis based on the angles among first principal component vectors of each family shape showed that families accomplish changes in elongation with a wide range of underlying modifications. Some groups such as Pomacentridae and Lethrinidae undergo decreases in body depth with proportional increases in all body regions, while other families show disproportionate changes in the length of the head (e.g., Labridae), the trunk or caudal region in all combinations (e.g., Pempheridae and Pinguipedidae). In conclusion, we found that evolutionary changes in body shape along an axis of elongation dominates diversification in reef fishes. Changes in shape on this axis are thought to have immediate implications for swimming performance, defense from gape limited predators, suction feeding performance and access to some highly specialized habitats. The morphological modifications that underlie changes in elongation are highly diverse, suggesting a role for a range of developmental processes and functional consequences.     

Patterns in Fluorescence over a Caribbean Reef Slope: the Coral Genus Madracis

Patterns of fluorescence and colony tissue, colour were studied (field observations and epifluorescence microscopy) in six species of the coral genus Madracis over depth from 10 to 60 m at a reef slope in Curaçao. Two functions showed up: (1) Decrease in number of colourmorphs (n = 25) with depth suggests a photo-protective function where short wavelengths (e.g. UV) are transformed to long wavelengths, (2) Green fluorescence, observed in four species over their entire depth range, transforms radiation to wavelengths useful for photosynthesis. The observed patterns in fluorescence between species did not correspond to the current taxonomic classification. Our results do not support the usefulness of fluorescence as a taxonomic tool in corals.