Background level of risk and the survival of predator-naive prey: can neophobia compensate for predator naivety in juvenile coral reef fishes?

Neophobia—the generalized fear response to novel stimuli—provides the first potential strategy that predator-naive prey may use to survive initial predator encounters. This phenotype appears to be highly plastic and present in individuals experiencing high-risk environments, but rarer in those experiencing low-risk environments. Despite the appeal of this strategy as a ‘solution’ for prey naivety, we lack evidence that this strategy provides any fitness benefit to prey. Here, we compare the relative effect of environmental risk (high versus low) and predator-recognition training (predator-naive versus predator-experienced individuals) on the survival of juvenile fish in the wild. We found that juveniles raised in high-risk conditions survived better than those raised in low-risk conditions, providing the first empirical evidence that environmental risk, in the absence of any predator-specific information, affects the way naive prey survive in a novel environment. Both risk level and experience affected survival; however, the two factors did not interact, indicating that the information provided by both factors did not interfere or enhance each other. From a mechanistic viewpoint, this indicates that the combination of the two factors may increase the intensity, and hence efficacy, of prey evasion strategies, or that both factors provide qualitatively separate benefits that would result in an additive survival success.     

Colour pattern as a single trait driving speciation in Hypoplectrus coral reef fishes?

Theory shows that speciation in the presence of gene flow occurs only under narrow conditions. One of the most favourable scenarios for speciation with gene flow is established when a single trait is both under disruptive natural selection and used to cue assortative mating. Here, we demonstrate the potential for a single trait, colour pattern, to drive incipient speciation in the genus Hypoplectrus (Serranidae), coral reef fishes known for their striking colour polymorphism. We provide data demonstrating that sympatric Hypoplectrus colour morphs mate assortatively and are genetically distinct. Furthermore, we identify ecological conditions conducive to disruptive selection on colour pattern by presenting behavioural evidence of aggressive mimicry, whereby predatory Hypoplectrus colour morphs mimic the colour patterns of non-predatory reef fish species to increase their success approaching and attacking prey. We propose that colour-based assortative mating, combined with disruptive selection on colour pattern, is driving speciation in Hypoplectrus coral reef fishes.     

Inferring gene flow in coral reef fishes from different molecular markers: which loci to trust?

Contrasting results are usually reported in the literature regarding the factors influencing observed structuring of genetic variability. The goals of this study were, for five coral reef fishes in French Polynesia, (1) to infer the theoretical variance of single locus F(ST) estimates expected under neutrality in order to exclude outlier loci before inferring gene flow and (2) to test thereafter whether species laying pelagic eggs effectively disperse more than species laying benthic eggs in this system. For this purpose, a total of 952 individuals from five species belonging to two families (Chaetodontidae and Pomacentridae) were screened among populations sampled within a 60-600 km spatial range for intron length polymorphism at 11 loci in order to illuminate contrasting results previously published on allozymes and mitochondrial DNA (mtDNA) control region polymorphisms. Statistically speaking, among the five species, four loci (three allozymes and one intron) were identified as outliers and discarded before interpretation of genetic differentiation in terms of effective dispersal. Biologically speaking, our results suggest that the observed genetic structure is not significantly related to the reproductive strategy of coral reef fish in the island system we analysed and that observed random genetic differentiation accommodates Wright's island model in all five species surveyed. Overall, our study emphasizes how cautious one has to be when trying to interpret present-day genetic structure in terms of gene flow while using a limited number of loci and/or different sets of loci.     

Do otolith increments allow correct inferences about age and growth of coral reef fishes?

Otolith increment structure is widely used to estimate age and growth of marine fishes. Here, I test the accuracy of the long-term otolith increment analysis of the lemon damselfish Pomacentrus moluccensis to describe age and growth characteristics. I compare the number of putative annual otolith increments (as a proxy for actual age) and widths of these increments (as proxies for somatic growth) with actual tagged fish-length data, based on a 6-year dataset, the longest time course for a coral reef fish. Estimated age from otoliths corresponded closely with actual age in all cases, confirming annual increment formation. However, otolith increment widths were poor proxies for actual growth in length [linear regression r ² = 0.44–0.90, n = 6 fish] and were clearly of limited value in estimating annual growth. Up to 60 % of the annual growth variation was missed using otolith increments, suggesting the long-term back calculations of otolith growth characteristics of reef fish populations should be interpreted with caution.     

Is there a reproductive basis to solitary living versus pair-formation in coral reef fishes?

Many species of coral reef fishes form pairs. While it is assumed that pairs represent the breeding unit of these species, the reproductive status of paired versus solitary individuals, and changes in status associated with pair-formation have seldom been investigated. In order to assess whether pairing is related to reproduction we examined whether the ontogenetic timing of pair formation coincided with the onset of maturation in four species of fishes: Chaetodon lunulatus and Chaetodon melannotus (family Chaetodontidae), and Valenciennea muralis and Valenciennea strigata (family Gobiidae). 65–78% of all fishes occurred in pairs. In C. lunulatus and V. muralis, pair-formation coincided with maturation, suggesting that these species form pairs for breeding. Further, C. lunulatus and V. muralis exhibited significant positive size-assortative pairing, which is often associated with monogamous mating. In contrast, pair formation in C. melannotus and V. strigata did not coincide with maturation. In both these species many solitary individuals were reproductive, and same sex pairs were common. While reproduction may be the basis for pairing in some species, both solitary and paired individuals are capable of breeding in others. We propose that non-reproductive mechanisms, such as predator vigilance, may explain pair-formation in coral reef fishes with non-monogamous breeding systems.     

Multiple disturbances and the global degradation of coral reefs: are reef fishes at risk or resilient?

Increased frequency of disturbances and anthropogenic activities are predicted to have a devastating impact on coral reefs that will ultimately change the composition of reef associated fish communities. We reviewed and analysed studies that document the effects of disturbance‐mediated coral loss on coral reef fishes. Meta‐analysis of 17 independent studies revealed that 62% of fish species declined in abundance within 3 years of disturbances that resulted in >10% decline in coral cover. Abundances of species reliant on live coral for food and shelter consistently declined during this time frame, while abundance of some species that feed on invertebrates, algae and/or detritus increased. The response of species, particularly those expected to benefit from the immediate loss of coral, is, however, variable and is attributed to erratic replenishment of stocks, ecological versatility of species and sublethal responses, such as changes in growth, body condition and feeding rates. The diversity of fish communities was found to be negatively and linearly correlated to disturbance‐mediated coral loss. Coral loss >20% typically resulted in a decline in species richness of fish communities, although diversity may initially increase following small declines in coral cover from high coverage. Disturbances that result in an immediate loss of habitat complexity (e.g. severe tropical storms), have a greater impact on fishes from all trophic levels, compared with disturbances that kill corals, but leave the reef framework intact (e.g. coral bleaching and outbreaks of Acanthaster planci). This is most evident among small bodied species and suggests the long‐term consequences of coral loss through coral bleaching and crown‐of‐thorn starfish outbreaks may be much more substantial than the short‐term effects currently documented.     

Temperature influences habitat preference of coral reef fishes: Will generalists become more specialised in a warming ocean?

Climate change is expected to pose a significant risk to species that exhibit strong behavioural preferences for specific habitat types, with generalist species assumed to be less vulnerable. In this study, we conducted habitat choice experiments to determine how water temperature influences habitat preference for three common species of coral reef damselfish (Pomacentridae) that differ in their levels of habitat specialisation. The lemon damselfish Pomacentrus moluccensis, a habitat specialist, consistently selected complex coral habitat across all temperature treatments (selected based on local average seasonal temperatures naturally experienced in situ: ambient winter 22°C; ambient summer 28°C; and elevated 31°C). Unexpectedly, the neon damselfish Pomacentrus coelestis and scissortail sergeant Abudefduf sexfasciatus, both of which have more generalist habitat associations, developed strong habitat preferences (for complex coral and boulder habitat, respectively) at the elevated temperature treatment (31°C) compared to no single preferred habitat at 22°C or 28°C. The observed shifts in habitat preference with temperature suggest that we may be currently underestimating the vulnerability of some habitat generalists to climate change and highlight that the ongoing loss of complex live coral through coral bleaching could further exacerbate resource overlap and species competition in ways not currently considered in climate change models.     

Do early life history characteristics determine species ranges and dispersal of coral reef fishes in the Indo‐Pacific?

The Indo‐Pacific consists of extensive continuous coastlines and many island groups of varying sizes and isolation. The species ranges of coral reef fishes vary enormously from Indo‐Pacific wide to highly endemic. There is also great variation in the early life history characteristics of coral reef fishes ( e.g . pelagic larval durations, spawning strategies and swimming abilities). We use individual‐based models (IBMs) to simulate the dispersal of coral reef fishes in the Indo‐Pacific. The development of dispersal strategies is explored based on ecological and geographical constraints. Simulations are presented for climatic and anthropogenically‐induced events.     

Will coral reef sponges be winners in the Anthropocene?

Recent observations have shown that increases in climate change‐related coral mortality cause changes in shallow coral reef community structure through phase shifts to alternative taxa. As a result, sponges have emerged as a potential candidate taxon to become a “winner,” and therefore a numerically and functionally dominant member of many coral reef communities. But, in order for this to occur, there must be sufficient trophic resources to support larger populations of these active filter‐feeding organisms. Globally, climate change is causing an increase in sea surface temperatures (SSTs) and a decrease in salinity, which can lead to an intensification in the stratification of shallow nearshore waters (0–200 m), that affects both the mixed layer depth (MLD) and the strength and duration of internal waves. Specifically, climate change‐driven increases in SSTs for tropical waters are predicted to cause increased stratification, and more stabilized surface waters. This causes a shallowing of the MLD which prevents nutrients from reaching the euphotic zone, and is predicted to decrease net primary production (NPP) up to 20% by the end of the century. Lower NPP would subsequently affect multiple trophic levels, including shallow benthic filter‐feeding communities, as the coupling between water column productivity and the benthos weakens. We argue here that sponge populations may actually be constrained, rather than promoted, by climate change due to decreases in their primary trophic resources, caused by bottom‐up forcing, secondary to physical changes in the water column (i.e., stratification and changes in the MLD resulting in lower nutrients and NPP). As a result, we predict sponge‐dominated tropical reefs will be rare, or short‐lived, if they occur at all into the future in the Anthropocene.     

Site fidelity and homing in tropical coral reef cardinalfish: are they using olfactory cues?

A number of tropical coral reef fish hold station and display restricted home ranges. If artificially displaced, they will return to their home site. We questioned if marine fish are using the same mechanisms for home site detection as many freshwater fish, that is, by olfactory sensing of chemical signals deposited on the substrate by conspecific fish. Behavioral experiments were conducted on Lizard Island Research Station, Queensland, Australia, in 2001 and 2002. Five-lined cardinalfish (Cheilodipterus quinquelineatus) were tested in groups with split-branded cardinalfish (Apogon compressus) as a reference species and individually against Apogon leptacanthus as well as conspecifics of another reef site. The group tests showed that both species preferred artificial reef sites that had previously been occupied by conspecifics. Individual C. quinquelineatus preferred scent of conspecifics from their own reef site to that from another site. They also preferred the scent released by artificial reefs previously occupied by conspecifics of their reef site to that of similar reefs previously occupied by conspecifics of another reef site. No discrimination between species from the same reef site was obtained in experiments with individual fish. Our data suggest that cardinalfish are keeping station and are homing by use of conspecific olfactory signals.     

Trophic separation in planktivorous reef fishes: a new role for mucus?

Oecologia - The feeding apparatus directly influences a species’ trophic ecology. In fishes, our understanding of feeding modes is largely derived from studies of rigid structures (i.e....     

Feeding by coral reef mesograzers: algae or cyanobacteria?

Marine studies on herbivory have addressed the role of algae as food and shelter for small consumers, but the potential of benthic cyanobacteria to play similar roles is largely unknown. Here, feeding preferences were measured for eight invertebrate consumers from Guam, offered four common macroalgae and two cyanobacteria. The survivorship of another consumer raised on either macroalgae or cyanobacteria was also assessed. From the choices offered, the sacoglossans Elysia rufescens and E. ornata consumed the green macroalga Bryopsis pennata. The crab Menaethius monoceros preferred the red alga Acanthophora spicifera. The amphipods Parhyale hawaiensis and Cymadusa imbroglio consumed macroalgae and cyanobacteria in equivalent amounts, with C. imbroglio showing less selectivity among diets. In contrast to these patterns, in these assays the gastropods Stylocheilus striatus, Haminoea cymbalum, H. ovalis, and Haminoea sp. fed exclusively, or survived only, on cyanobacteria. Preferences for different cyanobacteria varied. Field surveys of cyanobacteria-associated species yielded 34 different invertebrate taxa and suggested different degrees of specificity in these associations. Tropical mesograzers exploit considerably different food resources, with some species adapted to consume cyanobacterial mats. Benthic cyanobacteria may play important roles as food and shelter for marine consumers and may indirectly influence local biodiversity through their associated fauna.     

Stress and welfare in ornamental fishes: what can be learned from aquaculture?

The ornamental fish trade is estimated to handle up to 1·5 billion fishes. Transportation and handling of fishes imposes a range of stressors that can result in mortality at rates of up to 73%. These rates vary hugely, however, and can be as low as 2%, because they are generally estimated rather than based on experimental work. Given the numbers of ornamental fishes traded, any of the estimated mortality rates potentially incur significant financial losses and serious welfare issues. Industry bodies, such as the Ornamental Aquatic Trade Association (OATA), have established standards and codes of best practice for handling fishes, but little scientific research has been conducted to understand the links between stress, health and welfare in ornamental species. In aquaculture, many of the same stressors occur as those in the ornamental trade, including poor water quality, handling, transportation, confinement, poor social and physical environment and disease and in this sector directed research and some resulting interventions have resulted in improved welfare standards. This review considers the concept of welfare in fishes and evaluates reported rates of mortality in the ornamental trade. It assesses how the stress response can be quantified and used as a welfare indicator in fishes. It then analyses whether lessons from aquaculture can be usefully applied to the ornamental fish industry to improve welfare. Finally, this analysis is used to suggest how future research might be directed to help improve welfare in the ornamental trade.     

Adapt,move or die – how will tropical coral reef fishes cope with ocean warming?

Previous studies hailed thermal tolerance and the capacity for organisms to acclimate and adapt as the primary pathways for species survival under climate change. Here we challenge this theory. Over the past decade, more than 365 tropical stenothermal fish species have been documented moving poleward, away from ocean warming hotspots where temperatures 2–3 °C above long‐term annual means can compromise critical physiological processes. We examined the capacity of a model species – a thermally sensitive coral reef fish, Chromis viridis (Pomacentridae) – to use preference behaviour to regulate its body temperature. Movement could potentially circumvent the physiological stress response associated with elevated temperatures and may be a strategy relied upon before genetic adaptation can be effectuated. Individuals were maintained at one of six temperatures (23, 25, 27, 29, 31 and 33 °C) for at least 6 weeks. We compared the relative importance of acclimation temperature to changes in upper critical thermal limits, aerobic metabolic scope and thermal preference. While acclimation temperature positively affected the upper critical thermal limit, neither aerobic metabolic scope nor thermal preference exhibited such plasticity. Importantly, when given the choice to stay in a habitat reflecting their acclimation temperatures or relocate, fish acclimated to end‐of‐century predicted temperatures (i.e. 31 or 33 °C) preferentially sought out cooler temperatures, those equivalent to long‐term summer averages in their natural habitats (~29 °C). This was also the temperature providing the greatest aerobic metabolic scope and body condition across all treatments. Consequently, acclimation can confer plasticity in some performance traits, but may be an unreliable indicator of the ultimate survival and distribution of mobile stenothermal species under global warming. Conversely, thermal preference can arise long before, and remain long after, the harmful effects of elevated ocean temperatures take hold and may be the primary driver of the escalating poleward migration of species.     

What can morphology tell us about ecology of four invasive goby species?

This study presents a detailed comparative analysis of external morphology of four of the most invasive goby species in Europe (round goby Neogobius melanostomus, bighead goby Ponticola kessleri, monkey goby Neogobius fluviatilis and racer goby Ponticola gymnotrachelus) and interprets some ecological requirements of these species based on their morphological attributes. The results are evaluated within an ontogenetic context, and the morphological differences between the species are discussed in terms of the question: can special external shape adaptations help to assess the invasive potential of each species? The morphometric analyses demonstrate important differences between the four invasive gobies. Neogobius melanostomus appears to have the least specialized external morphology that may favour its invasive success: little specialization to habitat or diet means reduced restraints on overall ecological requirements. The other three species were found to possess some morphological specializations (P. kessleri to large prey, N. fluviatilis to sandy habitats and P. gymnotrachelus to macrophytes), but none of these gobies have managed to colonize such large areas or to reach such overall abundances as N. melanostomus.     

The phylogenetic relationships of the shags and cormorants: can sequence data resolve a disagreement between behavior and morphology?

Taxonomic arrangements for the cormorants and shags (Phalacrocoracidae) had varied greatly until two quite similar arrangements, one based on behavior and the other on osteological characters, became the basis for current thought on the evolutionary relationships of these birds. The terms cormorant and shag, which had previously been haphazardly applied to members of the group, became the vernacular terms for the two major subdivisions within this family. The two taxonomies differ in places, however, with the behavioral taxonomy placing several species within the shags and the osteological taxonomy and phylogeny grouping those species (as the marine cormorants) and placing them within the cormorants. In an attempt to resolve the differences in the relationships hypothesized by behavior and morphology, we sequenced three mitochondrial genes (12S, ATPase 6, and ATPase 8). Initial equally weighted parsimony trees differed slightly from our two weighted parsimony trees, one of which was also our maximum-likelihood tree. Many of the branches within our trees were well supported, but some sections of the phylogeny proved difficult to resolve with confidence. Our sequence trees differ substantially from the morphological phylogeny and show that neither the shags nor the cormorants are monophyletic, but form an intermingled group. Some of the groups supported by both the behavioral and the morphological taxonomies (e.g., the cliff shags, Stictocarbo) appear to be polyphyletic. Conversely, the monophyly of the blue-eyed shags, a traditional group that the osteological analysis had found to be paraphyletic, was supported by the sequence data. Until more taxa are sampled and a fully robust phylogeny is obtained, a conservative approach accepting a single genus, Phalacrocorax, for the shags and cormorants is recommended.     

Plants, pairing and phenotypes--two's company?

An RNA-based communication network appears to play a crucial role in regulating gene expression and in repressing viral and transposon sequences in plant genomes. In this article, we consider the evidence that gene expression might also be controlled epigenetically at a level other than non-coding RNA species-chromosome pairing. This epigenetic communication between sequences might be based--as it is in other organisms--on the physical pairing between homologues and the transfer of information between corresponding epigenetic landscapes. We suggest that paramutation might represent just one--albeit extreme and obvious--facet of a pairing-based gene expression regulation system in plants. Further exciting evidence for pairing occurring between homologues in plants is now mounting. An appreciation that pairing interactions might be important throughout plant development could assist in understanding phenomena such as endosperm imprinting, hybrid phenotypes and inbreeding depression.     

Root biomechanics in Rhizophora mangle: anatomy,morphology and ecology of mangrove’s flying buttresses

Background and AimsRhizophora species of mangroves have a conspicuous system of stilt-like roots (rhizophores) that grow from the main stem and resemble flying buttresses. As such, the development of rhizophores can be predicted to be important for the effective transmission of dynamic loads from the top of the tree to the ground, especially where the substrate is unstable, as is often the case in the habitats where Rhizophora species typically grow. This study tests the hypothesis that rhizophore architecture in R. mangle co-varies with their proximity to the main stem, and with stem size and crown position.Methods The allometry and wood mechanical properties of R. mangle (red mangrove) trees growing in a mangrove basin forest within a coastal lagoon in Mexico were compared with those of coexisting, non-buttressed mangrove trees of Avicennia germinans. The anatomy of rhizophores was related to mechanical stress due to crown orientation (static load) and to prevailing winds (dynamic load) at the study site.Key Results Rhizophores buttressed between 10 and 33 % of tree height. There were significant and direct scaling relationships between the number, height and length of rhizophores vs. basal area, tree height and crown area. Wood mechanical resistance was significantly higher in the buttressed R. mangle (modulus of elasticity, MOE = 18·1 ± 2 GPa) than in A. germinans (MOE = 12·1 ± 0·5 GPa). Slenderness ratios (total height/stem diameter) were higher in R. mangle, but there were no interspecies differences in critical buckling height. When in proximity to the main stem, rhizophores had a lower length/height ratio, higher eccentricity and higher xylem/bark and pith proportions. However, there were no directional trends with regard to prevailing winds or tree leaning.Conclusions In comparison with A. germinans, a tree species with wide girth and flare at the base, R. mangle supports a thinner stem of higher mechanical resistance that is stabilized by rhizophores resembling flying buttresses. This provides a unique strategy to increase tree slenderness and height in the typically unstable substrate on which the trees grow, at a site that is subject to frequent storms.     

Alloparental care in the sea: Brood parasitism and adoption within and between two species of coral reef Altrichthys damselfish?

The evolution of parental care opens the door for the evolution of brood parasitic strategies that allow individuals to gain the benefits of parental care without paying the costs. Here we provide the first documentation for alloparental care in coral reef fish and we discuss why these patterns may reflect conspecific and interspecific brood parasitism. Species‐specific barcodes revealed the existence of low levels (3.5% of all offspring) of mixed interspecific broods, mostly juvenile Amblyglyphidodon batunai and Pomacentrus smithi damselfish in Altrichthys broods. A separate analysis of conspecific parentage based on microsatellite markers revealed that mixed parentage broods are common in both species, and the genetic patterns are consistent with two different modes of conspecific brood parasitism, although further studies are required to determine the specific mechanisms responsible for these mixed parentage broods. While many broods had offspring from multiple parasites, in many cases a given brood contained only a single foreign offspring, perhaps a consequence of the movement of lone juveniles between nests. In other cases, broods contained large numbers of putative parasitic offspring from the same parents and we propose that these are more likely to be cases where parasitic adults laid a large number of eggs in the host nest than the result of movements of large numbers of offspring from a single brood after hatching. The evidence that these genetic patterns reflect adaptive brood parasitism, as well as possible costs and benefits of parasitism to hosts and parasites, are discussed.