Aggressive mimicry in a coral reef fish: The prey's view

Since all forms of mimicry are based on perceptual deception, the sensory ecology of the intended receiver is of paramount importance to test the necessary precondition for mimicry to occur, that is, model‐mimic misidentification, and to gain insight in the origin and evolutionary trajectory of the signals. Here we test the potential for aggressive mimicry by a group of coral reef fishes, the color polymorphic Hypoplectrus hamlets, from the point of view of their most common prey, small epibenthic gobies and mysid shrimp. We build visual models based on the visual pigments and spatial resolution of the prey, the underwater light spectrum and color reflectances of putative models and their hamlet mimics. Our results are consistent with one mimic‐model relationship between the butter hamlet H. unicolor and its model the butterflyfish Chaetodon capistratus but do not support a second proposed mimic‐model pair between the black hamlet H. nigricans and the dusky damselfish Stegastes adustus. We discuss our results in the context of color morphs divergence in the Hypoplectrus species radiation and suggest that aggressive mimicry in H. unicolor might have originated in the context of protective (Batesian) mimicry by the hamlet from its fish predators rather than aggressive mimicry driven by its prey.     

Habitat complexity modifies the impact of piscivores on a coral reef fish population

Patterns in juvenile mortality rates can have a profound affect on the distribution and abundance of adult individuals, and may be the result of a number of interacting factors. Field observations at Lizard Island (Great Barrier Reef, Australia) showed that for a coral reef damselfish, Pomacentrus moluccensis, juvenile mortality (over 1 year) varied between 20 and almost 100% among sites. Correlative data showed that juvenile mortality increased as a function of initial densities (recruitment), predator densities and the availability of preferred coral substrata. A multiple regression showed that these three variables together did not explain significantly more variation in mortality than the single factor showing the strongest relationship. This appeared to be because recruitment, predator densities and preferred coral substrata were all highly correlated, suggesting that one, two or all of these factors may be influencing juvenile mortality rates. One hypothesis was that density-dependent mortality in juveniles was the result of an interaction between predators (which appear to aggregate at high-recruitment sites) and the availability of preferred substrata (predator refuges). We tested this hypothesis by using both laboratory and field experiments to see whether fish predation could significantly alter survivorship of this damselfish, and whether this impact was dependent upon the coral substratum. The laboratory experiment was designed to test the effects of three common predators (Pseudochromis fuscus, Cephalopholis boenak and Thalassoma lunare) and three different coral substrata that varied in their complexity (Pocillopora damicornis, Acropora nasuta and A. nobilis) on the survival of juvenile Pomacentrus moluccensis. There was a significant interaction between predator species and microhabitat in determining survival. Pseudochromis fuscus and C. boenak were both significantly better at capturing juvenile damselfish than T. lunare. Juvenile survivorship was significantly better when they were given the more complex corals, Pocillopora damicornis and A. nasuta, compared with those given the open-structured species A. nobilis. This pattern reflects habitat selection in the field. Predators differed in their strike rates and the proportion of strikes that were successful, but all exhibited greater success at prey capture where A. nobilis was provided as shelter. The interaction between the effect of predator species and microhabitat structure on damselfish survival was tested in the field for a cohort of juvenile Pomacentrus moluccensis. We examined juvenile survival in the presence and absence of two predators that co-occur on natural patch reefs (C. boenak and Pseudochromis fuscus). The experimental patch reefs we used for this purpose were constructed from both high complexity (Pocillopora damicornis) and low complexity (A. nobilis) coral substrata. Both juveniles and predators were translocated to reefs at natural densities. The effects of predation were clearly dependent upon the microhabitat. Reefs of the high-complexity coral with predators supported the same high numbers of Pomacentrus moluccensis as the reefs with no resident predators. However, damselfish abundance was significantly lower on low-complexity reefs with resident predators, relative to the other treatments. Background rates of loss were high, even on preferred coral in the absence of the manipulated predator, suggesting that transient predators may be even more important than the residents. We suggest that adult abundances in this species were strongly influenced by the densities of different predators and the availability of preferred refuges. Received: 3 April 1997 / Accepted: 26 August 1997     

Island biogeography of Caribbean coral reef fish

Aim The goal of our study was to test fundamental predictions of biogeographical theories in tropical reef fish assemblages, in particular relationships between fish species richness and island area, isolation and oceanographic variables (temperature and productivity) in the insular Caribbean. These analyses complement an analogous and more voluminous body of work from the tropical Indo‐Pacific. The Caribbean is more limited in area with smaller inter‐island distances than the Indo‐Pacific, providing a unique context to consider fundamental processes likely to affect richness patterns of reef fish. Location Caribbean Sea. Methods We compiled a set of data describing reef‐associated fish assemblages from 24 island nations across the Caribbean Sea, representing a wide range of isolation and varying in land area from 53 to 110,860 km². Regression‐based analyses compared the univariate and combined effects of island‐specific physical predictors on fish species richness. Results We found that diversity of reef‐associated fishes increases strongly with increasing island area and with decreasing isolation. Richness also increases with increasing nearshore productivity. Analyses of various subsets of the entire data set reveal the robustness of the richness data and biogeographical patterns. Main conclusions Within the relatively small and densely packed Caribbean basin, fish species richness fits the classical species–area relationship. Richness also was related negatively to isolation, suggesting direct effects of dispersal limitation in community assembly. Because oceanic productivity was correlated with isolation, however, the related effects of system‐wide productivity on richness cannot be disentangled. These results highlight fundamental mechanisms that underlie spatial patterns of biodiversity among Caribbean coral reefs, and which are probably also are functioning in the more widespread and heterogeneous reefs of the Indo‐Pacific.     

Long-term cleaner fish presence affects growth of a coral reef fish

Cleaning behaviour is considered to be a classical example of mutualism. However, no studies, to our knowledge, have measured the benefits to clients in terms of growth. In the longest experimental study of its kind, over an 8 year period, cleaner fish Labroides dimidiatus were consistently removed from seven patch reefs (61-285 m(2)) and left undisturbed on nine control reefs, and the growth and parasite load of the damselfish Pomacentrus moluccensis determined. After 8 years, growth was reduced and parasitic copepod abundance was higher on fish from removal reefs compared with controls, but only in larger individuals. Behavioural observations revealed that P. moluccensis cleaned by L. dimidiatus were 27 per cent larger than nearby conspecifics. The selective cleaning by L. dimidiatus probably explains why only larger P. moluccensis individuals benefited from cleaning. This is the first demonstration, to our knowledge, that cleaners affect the growth rate of client individuals; a greater size for a given age should result in increased fecundity at a given time. The effect of the removal of so few small fish on the size of another fish species is unprecedented on coral reefs.     

Counts of coral reef fishes by an experienced observer are not biased by the number of target species

Fishes are commercially, recreationally and functionally important inhabitants of coral reefs. Accordingly, accurate assessments of fish abundance and diversity are necessary for effective reef management. While some reef fish monitoring programmes target all fishes, many survey a subset of common and visually obvious species. Changing to counts of all species, while desirable, risks new and unwelcome biases from altered observer swimming speeds and search patterns. Here we test whether substantially increasing the number of target species in an established fish monitoring programme biases counts of the original subset, so precluding ongoing comparisons with historical data. A subset of 141 fish species have been visually surveyed along 50 × 5 m transects over 27 years throughout Australia's Great Barrier Reef. We experimentally compared counts of the subset from standard subset-only surveys and from surveys of all species (excluding small site-attached fishes that are surveyed separately) at three diverse reefs. Subset species richness and abundance, in total and of major families, and assemblage structure did not differ due to survey method. The high-level experience of the one observer appeared to overcome new biases from counting more species and the extra 2 min/transect was not logistically excessive. Surveys of all fishes recorded almost 80% more species than subset-only surveys and >130% higher total abundance on average from >150% more genera that included abundant and functionally important taxa. Overall, fish counts by an experienced observer were not biased by the number of species surveyed and counts of all species markedly improved assessments of reef fish diversity and function.     

Strategies and trajectories of coral reef fish larvae optimizing self-recruitment

Like many marine organisms, most coral reef fishes have a dispersive larval phase. The fate of this phase is of great concern for their ecology as it may determine population demography and connectivity. As direct study of the larval phase is difficult, we tackle the question of dispersion from an opposite point of view and study self-recruitment. In this paper, we propose a mathematical model of the pelagic phase, parameterized by a limited number of factors (currents, predator and prey distributions, energy budgets) and which focuses on the behavioral response of the larvae to these factors. We evaluate optimal behavioral strategies of the larvae (i.e. strategies that maximize the probability of return to the natal reef) and examine the trajectories of dispersal that they induce. Mathematically, larval behavior is described by a controlled Markov process. A strategy induces a sequence, indexed by time steps, of "decisions" (e.g. looking for food, swimming in a given direction). Biological, physical and topographic constraints are captured through the transition probabilities and the sets of possible decisions. Optimal strategies are found by means of the so-called stochastic dynamic programming equation. A computer program is developed and optimal decisions and trajectories are numerically derived. We conclude that this technique can be considered as a good tool to represent plausible larval behaviors and that it has great potential in terms of theoretical investigations and also for field applications.     

A dynamic model of group-size choice in the coral reef fish Dascyllus albisella

We developed a dynamic programming model of group size choicefor settling coral reef fish to help understand variabilityin observed group sizes. Rather than calculating optimal groupsize, we modeled optimal choice and calculated the acceptablegroup sizes that arose from this choice. In the model, settling individualsweigh the fitness value of settling in a group against the expectedfitness of searching another day and encountering other groups, choosingthe option with the higher value. Model results showed that individualssettling on any given day in the settling season have several acceptablegroup sizes in which they can settle. The range of acceptablegroup sizes also changes across the season. Early in the season,when there is still adequate time to grow, large groups (withhigher survival) have the highest fitness. Late in the season,when the ability to grow fast becomes more important, smallgroups, which convey fast growth rates (although riskier), havehigher fitness. Thus, according to our model, even when fishall make the same, simple decisions, a variety of outcomes arepossible, depending on the specific options encountered andtemporally changing ecological pressures. Even when all fishbehave optimally, initial variability in group sizes will persist.     

Similar regional effects among local habitats on the structure of tropical reef fish and coral communities

Aim We examined data on corals and reef fishes to determine how particular local habitat types contribute to variation in community structure across regions covering gradients in species richness and how consistent this was over time. Location Great Barrier Reef (GBR), Australia. Methods We compared large‐scale (1300 km), long‐term (11 years) data on fishes and corals that were collected annually at fixed sites in three habitats (inshore, mid‐shelf and outer‐shelf reefs) and six regions (latitudinal sectors) along a gradient of regional species richness in both communities. We used canonical approaches to partition variation in community structure (sites × species abundance data matrices) into components associated with habitat, region and time and Procrustes analyses to assess the degree of concordance between coral and fish community structure. Results Remarkably similar patterns emerged for both fish and coral communities occupying the same sites. Reefs that had similar coral communities also had similar fish communities. The fraction of the community data that could be explained by regional effects, independent of pure habitat effects, was similar in both fish (33%) and coral (36.9%) communities. Pure habitat effects were slightly greater in the fish (31.3%) than in the coral (20.1%) community. Time explained relatively little variation (fish = 7.9%, corals = 9.6%) compared with these two spatial factors. Conclusions Our results indicate either that fish and coral communities were structured in similar ways by processes associated with region, habitat and time, or that the variation in fish community structure tracked variation associated with the coral communities at these sites and thereby reflects an indirect link between the environment and the structure of fish communities mediated by corals. Irrespective of the causes of such commonality, we demonstrate that community structure, not just species richness, can be related to both habitat differences and regional setting simultaneously.     

Elevated carbon dioxide affects behavioural lateralization in a coral reef fish

Elevated carbon dioxide (CO(2)) has recently been shown to affect chemosensory and auditory behaviour, and activity levels of larval reef fishes, increasing their risk of predation. However, the mechanisms underlying these changes are unknown. Behavioural lateralization is an expression of brain functional asymmetries, and thus provides a unique test of the hypothesis that elevated CO(2) affects brain function in larval fishes. We tested the effect of near-future CO(2) concentrations (880 μatm) on behavioural lateralization in the reef fish, Neopomacentrus azysron. Individuals exposed to current-day or elevated CO(2) were observed in a detour test where they made repeated decisions about turning left or right. No preference for right or left turns was observed at the population level. However, individual control fish turned either left or right with greater frequency than expected by chance. Exposure to elevated-CO(2) disrupted individual lateralization, with values that were not different from a random expectation. These results provide compelling evidence that elevated CO(2) directly affects brain function in larval fishes. Given that lateralization enhances performance in a number of cognitive tasks and anti-predator behaviours, it is possible that a loss of lateralization could increase the vulnerability of larval fishes to predation in a future high-CO(2) ocean.     

Positive indirect effects in a coral reef fish community

Indirect effects occur when two species interact through one or more intermediate species. Theoretical studies indicate that indirect interactions between two prey types that share common predators can be positive, neutral or negative. We document a positive indirect interaction between different types of prey fish on coral reefs in Australia. A high abundance of one type of prey fish (cardinalfishes: Apogonidae) resulted in higher recruitment, abundance and species richness of other prey fish. Our evidence indicates that these effects were not due to differential settlement but were instead due to differential post-settlement predation. We hypothesize that resident piscivores altered their foraging behaviour by concentrating on highly abundant cardinal-fish when they were present, leaving recruits of other species relatively unmolested. Indirect effects were evident within 48 h of settlement and persisted throughout the 42-day experiment, highlighting the importance of early post-settlement processes in these communities.     

Effects of coral restoration on fish communities: snapshots of long‐term,multiregional responses and implications for practice

Coral restoration is widely used around the world to address dramatic declines in coral cover; however, very few studies have looked specifically at the temporal response of fish assemblages (i.e. abundance and diversity) to coral restoration. Several critical reef functions and processes are driven by fishes, thereby making their recovery and responses around restoration structures key indicators of success. This study evaluates fish abundance and community composition on restoration plots following 8–12 years of restoration activity, in four locations (two Caribbean and two Indo‐Pacific). Responses were very complex with region‐, site‐, and body size‐specific patterns. Overall, fish abundance only increased in Indo‐Pacific sites where damselfish responded positively to increased coral cover and topographic complexity. Restoration effects on other fish families and particularly on larger bodied reef fish were negative or neutral at all locations. If restoration initiatives are going to substantively improve the condition and recovery of degraded reef fish communities, restoration efforts need to be planned, designed, and monitored based on fish‐specific habitat requirements and locally specific community dynamics.     

Within and between day variability in coral reef fish assemblages: Implications for fish community surveys

Coral reef ecosystems are under increasing anthropogenic pressures making it ever more important to monitor changes in fish communities to implement appropriate management. In contrast to long-term spatial and temporal variation which has been extensively documented, little work has been carried out to identify variability in fish assemblages on short time scales, with few studies testing patterns of fish assemblages between and within days. Here we investigated the diurnal changes in species richness, relative abundance and assemblage composition in a shallow coral reef fish community in Egypt. To do so, a section of coral reef was filmed during the morning (0600 h), midday (1000 and 1400 h) and afternoon (1800 h) over eleven days. Dusk (0600 h) and dawn samples (1800 h) showed higher species richness compared to late morning (1000 h) and mid-day samples (1400 h) and borderline significantly higher numbers of total individuals, likely associated with feeding activity and predator avoidance. Assemblage composition varied across days and time-of-day, showing greater variability during dusk and dawn associated with a transition between day-time and night-time assemblages. Our results have implications for designing coral reef fish surveys, emphasising that short-term changes in fish communities should be considered when designing experiments to monitor fish assemblages over time. Where possible, we suggest increasing replication within sites and time scales or randomising data within a specific time window at all sites, looking to exclude dusk and dawn.     

Predation risk assessment by olfactory and visual cues in a coral reef fish

Assessment of predation risk is vital for the success of an individual. Primary cues for the assessment include visual and olfactory stimuli, but the relative importance of these sources of information for risk assessment has seldom been assessed for marine fishes. This study examined the importance of visual and chemical cues in assessing risk for the star goby, Asterropteryx semipunctatus. Visual and chemical cue intensities were used that were indicative of a high threat situation. The behavioural response elicited by both the visual cues of a predator (the rock cod, Cephalopholis boenak) and the chemical alarm cues from conspecifics were similar in magnitude, with responses including a decrease in feeding strikes and moves. A bobbing behaviour was exhibited when the predator was visible and not when only exposed to the chemical alarm cue. When visual and chemical cues were presented together they yielded a stronger antipredator response than when gobies were exposed solely to conspecific alarm cues. This suggests additivity of risk assessment information at the levels of threat used, however, the goby’s response is also likely to depend on the environmental and social context of the predator–prey encounter. This study highlights the importance of chemical cues in the assessment of predation risk for a coral reef fish.     

Effects of EMF emissions from undersea electric cables on coral reef fish

The objective of this study was to determine if electromagnetic field (EMF) emissions from undersea power cables impacted local marine life, with an emphasis on coral reef fish. The work was done at the South Florida Ocean Measurement Facility of Naval Surface Warfare Center in Broward County, Florida, which has a range of active undersea detection and data transmission cables. EMF emissions from a selected cable were created during non‐destructive visual fish surveys on SCUBA. During surveys, the transmission of either alternating current (AC), direct current (DC), or none (OFF) was randomly initiated by the facility at a specified time. Visual surveys were conducted using standardized transect and point‐count methods to acquire reef fish abundances and species richness prior to and immediately after a change in transmission frequency. The divers were also tasked to note the reaction of the reef fish to the immediate change in EMF during a power transition. In general, analysis of the data did not find statistical differences among power states and any variables. However, this may be a Type II error as there are strong indications of a potential difference of a higher abundance of reef fish at the sites when the power was off, and further study is warranted. Bioelectromagnetics. 39:35–52, 2018. © 2017 Wiley Periodicals, Inc.     

Cyanide fishing and cyanide detection in coral reef fish using chemical tests and biosensors

Sodium cyanide has been used in the Philippines to collect tropical marine fish for aquarium and food trades since the early 1960s. Cyanide fishing is a fast method to stun and collect fish. This practice is damaging the coral reefs irreversibly. In most countries cyanide fishing is illegal, but most of the exporting and importing countries do not have test and certificate systems. Many analytical methods are available for the detection of cyanide in environmental and biological samples. However, most of the techniques are time consuming, and some lack specificity or sensitivity. Besides, an ultra sensitive cyanide detection method is needed due to the rapid detoxification mechanisms in fish. The aim of this review is to give an overview of cyanide fishing problem in the south-east Asia and current strategies to combat this destructive practice, summarise some of the methods for cyanide detection in biological samples and their disadvantages. A novel approach to detect cyanide in marine fish tissues is briefly discussed.     

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.     

Characterization of 16 microsatellite loci for a common coral reef fish,the fierce shrimpgoby Ctenogobiops feroculus

We developed 16 pairs of primers for microsatellite loci of the fierce shrimpgoby, Ctenogobiops feroculus. Analysis of 35–40 gobies per locus from five islands in French Polynesia indicated that allele frequency varied from two to 30 per locus, while observed heterozygosity ranged between 0.05 and 0.98. These microsatellites should provide insight into patterns of dispersal and connectivity among populations of this common coral reef fish.