Ability to home in small site‐attached coral reef fishes

The ability of two common, site‐attached coral‐reef fishes to return to their home corals after displacement was investigated in a series of field experiments at One Tree Island, southern Great Barrier Reef. The humbug Dascyllus aruanus was displaced up to 250 m, with 42% of individuals returning home, irrespective of body size, displacement, direction (up or across currents) and route complexity, while for the lemon damselfish Pomacentrus moluccensis 35% of individuals returned overall, with 33% from the greatest displacement, 100 m along a reef edge. Given that the home range of both species is <1 m², over their 10+ year life span, the mechanisms and motivations for such homing ability are unclear but it may allow resilience if fishes are displaced by storm events, allowing rapid return to home corals.     

Mass coral bleaching causes biotic homogenization of reef fish assemblages

Global climate change is altering community composition across many ecosystems due to nonrandom species turnover, typically characterized by the loss of specialist species and increasing similarity of biological communities across spatial scales. As anthropogenic disturbances continue to alter species composition globally, there is a growing need to identify how species responses influence the establishment of distinct assemblages, such that management actions may be appropriately assigned. Here, we use trait‐based analyses to compare temporal changes in five complementary indices of reef fish assemblage structure among six taxonomically distinct coral reef habitats exposed to a system‐wide thermal stress event. Our results revealed increased taxonomic and functional similarity of previously distinct reef fish assemblages following mass coral bleaching, with changes characterized by subtle, but significant, shifts toward predominance of small‐bodied, algal‐farming habitat generalists. Furthermore, while the taxonomic or functional richness of fish assemblages did not change across all habitats, an increase in functional originality indicated an overall loss of functional redundancy. We also found that prebleaching coral composition better predicted changes in fish assemblage structure than the magnitude of coral loss. These results emphasize how measures of alpha diversity can mask important changes in the structure and functioning of ecosystems as assemblages reorganize. Our findings also highlight the role of coral species composition in structuring communities and influencing the diversity of responses of reef fishes to disturbance. As new coral species configurations emerge, their desirability will hinge upon the composition of associated species and their capacity to maintain key ecological processes in spite of ongoing disturbances.     

Extinction vulnerability of coral reef fishes

With rapidly increasing rates of contemporary extinction, predicting extinction vulnerability and identifying how multiple stressors drive non-random species loss have become key challenges in ecology. These assessments are crucial for avoiding the loss of key functional groups that sustain ecosystem processes and services. We developed a novel predictive framework of species extinction vulnerability and applied it to coral reef fishes. Although relatively few coral reef fishes are at risk of global extinction from climate disturbances, a negative convex relationship between fish species locally vulnerable to climate change vs. fisheries exploitation indicates that the entire community is vulnerable on the many reefs where both stressors co-occur. Fishes involved in maintaining key ecosystem functions are more at risk from fishing than climate disturbances. This finding is encouraging as local and regional commitment to fisheries management action can maintain reef ecosystem functions pending progress towards the more complex global problem of stabilizing the climate.     

A coral reef refuge in the Red Sea

The stability and persistence of coral reefs in the decades to come is uncertain due to global warming and repeated bleaching events that will lead to reduced resilience of these ecological and socio‐economically important ecosystems. Identifying key refugia is potentially important for future conservation actions. We suggest that the Gulf of Aqaba (GoA) (Red Sea) may serve as a reef refugium due to a unique suite of environmental conditions. Our hypothesis is based on experimental detection of an exceptionally high bleaching threshold of northern Red Sea corals and on the potential dispersal of coral planulae larvae through a selective thermal barrier estimated using an ocean model. We propose that millennia of natural selection in the form of a thermal barrier at the southernmost end of the Red Sea have selected coral genotypes that are less susceptible to thermal stress in the northern Red Sea, delaying bleaching events in the GoA by at least a century.     

Dietary generalism accelerates arrival and persistence of coral‐reef fishes in their novel ranges under climate change

Climate change is redistributing marine and terrestrial species globally. Life‐history traits mediate the ability of species to cope with novel environmental conditions, and can be used to gauge the potential redistribution of taxa facing the challenges of a changing climate. However, it is unclear whether the same traits are important across different stages of range shifts (arrival, population increase, persistence). To test which life‐history traits most mediate the process of range extension, we used a 16‐year dataset of 35 range‐extending coral‐reef fish species and quantified the importance of various traits on the arrival time (earliness) and degree of persistence (prevalence and patchiness) at higher latitudes. We show that traits predisposing species to shift their range more rapidly (large body size, broad latitudinal range, long dispersal duration) did not drive the early stages of redistribution. Instead, we found that as diet breadth increased, the initial arrival and establishment (prevalence and patchiness) of climate migrant species in temperate locations occurred earlier. While the initial incursion of range‐shifting species depends on traits associated with dispersal potential, subsequent establishment hinges more on a species’ ability to exploit novel food resources locally. These results highlight that generalist species that can best adapt to novel food sources might be most successful in a future ocean.     

Parasite acquisition by larval coral‐reef fishes

Of 164 fish larvae belonging to 11 species sampled from the island of Moorea, French Polynesia, 30% had at least one parasite individual and parasite prevalence ranged between 0 for Chaetodon citrinellus and 80% for Parupeneus barberinus. Parasites were present only in larvae that had fed and were present in the gut but absent from gills, body cavity and muscle. Parasites appeared to be acquired by ingestion of intermediate hosts when the larvae fed on the outer slope, prior to reef colonization.     

Fishing degrades size structure of coral reef fish communities

Fishing pressure on coral reef ecosystems has been frequently linked to reductions of large fishes and reef fish biomass. Associated impacts on overall community structure are, however, less clear. In size‐structured aquatic ecosystems, fishing impacts are commonly quantified using size spectra, which describe the distribution of individual body sizes within a community. We examined the size spectra and biomass of coral reef fish communities at 38 US‐affiliated Pacific islands that ranged in human presence from near pristine to human population centers. Size spectra ‘steepened’ steadily with increasing human population and proximity to market due to a reduction in the relative biomass of large fishes and an increase in the dominance of small fishes. Reef fish biomass was substantially lower on inhabited islands than uninhabited ones, even at inhabited islands with the lowest levels of human presence. We found that on populated islands size spectra exponents decreased (analogous to size spectra steepening) linearly with declining biomass, whereas on uninhabited islands there was no relationship. Size spectra were steeper in regions of low sea surface temperature but were insensitive to variation in other environmental and geomorphic covariates. In contrast, reef fish biomass was highly sensitive to oceanographic conditions, being influenced by both oceanic productivity and sea surface temperature. Our results suggest that community size structure may be a more robust indicator than fish biomass to increasing human presence and that size spectra are reliable indicators of exploitation impacts across regions of different fish community compositions, environmental drivers, and fisheries types. Size‐based approaches that link directly to functional properties of fish communities, and are relatively insensitive to abiotic variation across biogeographic regions, offer great potential for developing our understanding of fishing impacts in coral reef ecosystems.     

Temperature‐driven coral decline: the role of marine protected areas

Warming ocean temperatures are considered to be an important cause of the degradation of the world's coral reefs. Marine protected areas (MPAs) have been proposed as one tool to increase coral reef ecosystem resistance and resilience (i.e. recovery) to the negative effects of climate change, yet few studies have evaluated their efficacy in achieving these goals. We used a high resolution 4 km global temperature anomaly database from 1985–2005 and 8040 live coral cover surveys on protected and unprotected reefs to determine whether or not MPAs have been effective in mitigating temperature‐driven coral loss. Generally, protection in MPAs did not reduce the effect of warm temperature anomalies on coral cover declines. Shortcomings in MPA design, including size and placement, may have contributed to the lack of an MPA effect. Empirical studies suggest that corals that have been previously exposed to moderate levels of thermal stress have greater adaptive capacity and resistance to future thermal stress events. Existing MPAs protect relatively fewer reefs with moderate anomaly frequencies, potentially reducing their effectiveness. However, our results also suggest that the benefits from MPAs may not be great enough to offset the magnitude of losses from acute thermal stress events. Although MPAs are important conservation tools, their limitations in mitigating coral loss from acute thermal stress events suggest that they need to be complemented with policies aimed at reducing the activities responsible for climate change.     

Vertical zonation of coral reef fishes in the Sudanese Red Sea

The vertical zonation of 38 species of fish inhabiting coral reefs in the Sudanese Red Sea is described. A marked degree of vertical zonation of the fishes is shown to exist. The usefulness of a depth oriented survey method for studying reef fish is discussed in relation to these results.General relationships between vertical zonation and species diversity are noted.     

Habitat degradation disrupts neophobia in juvenile coral reef fish

Habitat degradation not only disrupts habitat‐forming species, but alters the sensory landscape within which most species must balance behavioural activities against predation risk. Rapidly developing a cautious behavioural phenotype, a condition known as neophobia, is advantageous when entering a novel risky habitat. Many aquatic organisms rely on damage‐released conspecific cues (i.e. alarm cues) as an indicator of impending danger and use them to assess general risk and develop neophobia. This study tested whether settlement‐stage damselfish associated with degraded coral reef habitats were able to use alarm cues as an indicator of risk and, in turn, develop a neophobic response at the end of their larval phase. Our results indicate that fish in live coral habitats that were exposed to alarm cues developed neophobia, and, in situ, were found to be more cautious, more closely associated with their coral shelters and survived four‐times better than non‐neophobic control fish. In contrast, fish that settled onto degraded coral habitats did not exhibit neophobia and consequently suffered much greater mortality on the reef, regardless of their history of exposure to alarm cues. Our results show that habitat degradation alters the efficacy of alarm cues with phenotypic and survival consequences for newly settled recruits.     

Composition and structure of reef fish communities in Paraíba State,north‐eastern Brazil

The composition and trophic structure of reef fish communities in two natural and two artificial reefs along the coast of Paraíba State in north‐eastern Brazil were investigated. A total of 114 species of fish belonging to 47 families were recorded during 120 stationary visual surveys, slightly less than half (46·55%) of which were recorded at all four surveyed localities. Most species are widely distributed on the western Atlantic coast, but several are endemic to Brazil. The greatest diversity and equitability indexes were recorded at the reefs of Sapatas and Cabeço dos Cangulos, whereas the greatest richness and abundance were found at the Queimado shipwreck. The Alvarenga shipwreck reef had the least richness, diversity and equitability. The four localities studied had very similar ichthyofaunas, especially in relation to species composition. The reefs along the Paraíba coast are considered priority conservation areas by the Brazilian Ministry of the Environment, and the information generated by this study will be useful for comparison with other reefs in the region and can be directly applied to programmes seeking to protect and manage these environments.     

Body size determines eyespot size and presence in coral reef fishes

Numerous organisms display conspicuous eyespots. These eye‐like patterns have been shown to effectively reduce predation by either deflecting strikes away from nonvital organs or by intimidating potential predators. While investigated extensively in terrestrial systems, determining what factors shape eyespot form in colorful coral reef fishes remains less well known. Using a broadscale approach we ask: How does the size of the eyespot relate to the actual eye, and at what size during ontogeny are eyespots acquired or lost? We utilized publicly available images to generate a dataset of 167 eyespot‐bearing reef fish species. We measured multiple features relating to the size of the fish, its eye, and the size of its eyespot. In reef fishes, the area of the eyespot closely matches that of the real eye; however, the eyespots “pupil” is nearly four times larger than the real pupil. Eyespots appear at about 20 mm standard length. However, there is a marked decrease in the presence of eyespots in fishes above 48 mm standard length; a size which is tightly correlated with significant decreases in documented mortality rates. Above 75–85 mm, the cost of eyespots appears to outweigh their benefit. Our results identify a “size window” for eyespots in coral reef fishes, which suggests that eyespot use is strictly body size‐dependent within this group.     

A low-cost procedure for automatic seafloor mapping, with particular reference to coral reef conservation in developing nations

Loss of marine biodiversity through benthic habitat destruction has created urgent needs for low-cost, high-performance seafloor survey methods. However, accurate seafloor mapping and classification is usually an expensive undertaking requiring sophisticated equipment, which excludes important low-budget user groups in developing nations. In this paper, we introduce a low-cost procedure for seafloor mapping based on free-of-charge data acquisition software that can be downloaded from the Internet. Using a Malaysian coral-reef case-study, we show how comprehensive bathymetric mapping can be implemented with such software using inexpensive eccosounder and GPS, and describe principles for integration of environmental data, either by connecting additional instruments to the computer (up to 32 instruments with up to eight channels each can be handled simultaneously), or by using simple synchronisation techniques with equipment that records to separate media, such as video cameras. We mapped a Malaysian coral-reef area of 114 hectares in 6 hours of video mapping, achieving reef mapping rates that matches rates currently achieved only with air-borne imaging devices. However, the present methodology results in completely ground-truthed data that can be classified according to many schemes by direct observation of the habitat, and provides detailed bathymetric data that satellite imagery or air-borne spectrographic sensors do not provide. The method can be used as a stand-alone reef mapping and classification tool on the scale of tens to hundreds of square kilometres. On larger scales (thousands of square kilometres), airborne survey methods are likely to remain more cost-effective than boat-based methods, yet also in such settings this simple method offer unprecedented capacity for ground truthing and thereby increased capacity for habitat classification.     

Turbid reefs moderate coral bleaching under climate‐related temperature stress

Thermal‐stress events that cause coral bleaching and mortality have recently increased in frequency and severity. Yet few studies have explored conditions that moderate coral bleaching. Given that high light and high ocean temperature together cause coral bleaching, we explore whether corals at turbid localities, with reduced light, are less likely to bleach during thermal‐stress events than corals at other localities. We analyzed coral bleaching, temperature, and turbidity data from 3,694 sites worldwide with a Bayesian model and found that K_d490, a measurement positively related to turbidity, between 0.080 and 0.127 reduced coral bleaching during thermal‐stress events. Approximately 12% of the world's reefs exist within this “moderating turbidity” range, and 30% of reefs that have moderating turbidity are in the Coral Triangle. We suggest that these turbid nearshore environments may provide some refuge through climate change, but these reefs will need high conservation status to sustain them close to dense human populations.     

Climate‐driven disparities among ecological interactions threaten kelp forest persistence

The combination of ocean warming and acidification brings an uncertain future to kelp forests that occupy the warmest parts of their range. These forests are not only subject to the direct negative effects of ocean climate change, but also to a combination of unknown indirect effects associated with changing ecological landscapes. Here, we used mesocosm experiments to test the direct effects of ocean warming and acidification on kelp biomass and photosynthetic health, as well as climate‐driven disparities in indirect effects involving key consumers (urchins and rock lobsters) and competitors (algal turf). Elevated water temperature directly reduced kelp biomass, while their turf‐forming competitors expanded in response to ocean acidification and declining kelp canopy. Elevated temperatures also increased growth of urchins and, concurrently, the rate at which they thinned kelp canopy. Rock lobsters, which are renowned for keeping urchin populations in check, indirectly intensified negative pressures on kelp by reducing their consumption of urchins in response to elevated temperature. Overall, these results suggest that kelp forests situated towards the low‐latitude margins of their distribution will need to adapt to ocean warming in order to persist in the future. What is less certain is how such adaptation in kelps can occur in the face of intensifying consumptive (via ocean warming) and competitive (via ocean acidification) pressures that affect key ecological interactions associated with their persistence. If such indirect effects counter adaptation to changing climate, they may erode the stability of kelp forests and increase the probability of regime shifts from complex habitat‐forming species to more simple habitats dominated by algal turfs.     

Fine‐scale foraging behavior reveals differences in the functional roles of herbivorous reef fishes

Efforts to understand and protect ecosystem functioning have put considerable emphasis on classifying species according to the functions they perform. However, coarse classifications based on diet or feeding mode often oversimplify species'' contributions to ecological processes. Behavioral variation among superficially similar species is easily missed but could indicate important differences in competitive interactions and the spatial scale at which species deliver their functions. To test the extent to which behavior can vary within existing functional classifications, we investigate the diversity of foraging movements in three herbivorous coral reef fishes across two functional groups. We find significant variation in foraging movements and spatial scales of operation between species, both within and across existing functional groups. Specifically, we show that movements and space use range from low frequency foraging bouts separated by short distances and tight turns across a small area, to high frequency, far‐ranging forays separated by wide sweeping turns. Overall, we add to the burgeoning evidence that nuanced behavioral differences can underpin considerable complementarity within existing functional classifications, and that species assemblages may be considerably less redundant than previously thought.     

Elevated temperature reduces the respiratory scope of coral reef fishes

The capacity for marine fishes to perform aerobically (aerobic scope) is predicted to control their thermal tolerance and, thus, the impact that rapid climate change will have on their populations. We tested the effect of increased water temperatures on the resting and maximum rates of oxygen consumption in five common coral reef fishes at Lizard Island on the northern Great Barrier Reef, Australia. All species exhibited a decline in aerobic capacity at elevated water temperatures (31, 32 or 33 °C) compared with controls (29 °C); however, the response was much stronger in two cardinalfishes, Ostorhinchus cyanosoma and O. doederleini , compared with three damselfishes, Dascyllus anuarus, Chromis atripectoralis and Acanthochromis polyacanthus . Aerobic scope of the two cardinalfishes was reduced by nearly half at 31 °C compared with 29 °C, and virtually all capacity for additional oxygen uptake was exhausted by 33 °C. In contrast, the three damselfishes retained over half their aerobic scope at 33 °C. Such differences in thermal tolerance between species, and possibly families, suggest that the community structure of reef fish assemblages might change significantly as ocean temperatures increase. Populations of thermally tolerant species are likely to persist at higher temperatures, but populations of thermally sensitive species could decline on low-latitude reefs if individual performance falls below levels needed to sustain viable populations.     

Nocturnal relocation of adult and juvenile coral reef fishes in response to reef noise

Juvenile and adult reef fishes often undergo migration, ontogenic habitat shifts, and nocturnal foraging movements. The orientation cues used for these behaviours are largely unknown. In this study, the use of sound as an orientation cue guiding the nocturnal movements of adult and juvenile reef fishes at Lizard Island, Great Barrier Reef was examined. The first experiment compared the movements of fishes to small patch reefs where reef noise was broadcast, with those to silent reefs. No significant responses were found in the 79 adults that were collected, but the 166 juveniles collected showed an increased diversity each morning on the reefs with broadcast noise, and significantly greater numbers of juveniles from three taxa (Apogonidae, Gobiidae and Pinguipedidae) were collected from reefs with broadcast noise. The second experiment compared the movement of adult and juvenile fishes to reefs broadcasting high (>570 Hz), or low (<570 Hz) frequency reef noise, or to silent reefs. Of the 122 adults collected, the highest diversity was seen at the low frequency reefs; and adults from two families (Gobiidae and Blenniidae) preferred these reefs. A similar trend was observed in the 372 juveniles collected, with higher diversity at the reefs with low frequency noises. This preference was seen in the juvenile apogonids; however, juvenile gobiids were attracted to both high and low sound treatments equally, and juvenile stage Acanthuridae preferred the high frequency noises. This evidence that juvenile and adult reef fishes orientate with respect to the soundscape raises important issues for management, conservation and the protection of sound cues used in natural behaviour.