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Increased levels of dissolved carbon dioxide (CO2) drive ocean acidification and have been predicted to increase the energy use of marine fishes via physiological and behavioural mechanisms. This notion is based on a theoretical framework suggesting that detrimental effects on energy use are caused by plasma acid–base disruption in response to hypercapnic acidosis, potentially in combination with a malfunction of the gamma aminobutyric acid type A (GABAA) receptors in the brain. However, the existing empirical evidence testing these effects primarily stems from studies that exposed fish to elevated CO2 for a few days and measured a small number of traits. We investigated a range of energetic traits in juvenile spiny chromis damselfish (Acanthochromis polyacanthus) over 3 months of acclimation to projected end-of-century CO2 levels (~ 1000 µatm). Somatic growth and otolith size and shape were unaffected by the CO2 treatment across 3 months of development in comparison with control fish (~ 420 µatm). Swimming activity during behavioural assays was initially higher in the elevated CO2 group, but this effect dissipated within ~ 25 min following handling. The transient higher activity of fish under elevated CO2 was not associated with a detectable difference in the rate of oxygen uptake nor was it mediated by GABAA neurotransmitter interference because treatment with a GABAA antagonist (gabazine) did not abolish the CO2 treatment effect. These findings contrast with several short-term studies by suggesting that end-of-century levels of CO2 may have negligible direct effects on the energetics of at least some species of fish.

The transition from a planktonic larval stage to a benthic or demersal juvenile stage, “recruitment”, is a crucial event in the life history of coral reef fishes, and has a strong influence on population size. Predation by piscivorous fishes is thought to be the main determinant of recruitment success, and has received the most attention. However, recent studies suggest that recently settled reef fishes are also an important target of micropredation from blood-feeding ectoparasites which may have significant lethal and sublethal effects. In this study, we quantified the relationship between levels of infestation by gnathiid isopods and mortality rates among juveniles of three species of reef fishes as a function of body mass both within and among species. We found that a single gnathiid isopod larva could kill fish of all three species shortly after settlement, up to 0.116 g [18 mm fork length (FL)] in French grunt (Haemulon flavolineatum), 0.027 g (15 mm FL) in masked goby (Coryphopterus personatus) and 0.01 g (9 mm FL) in beaugregory damselfish (Stegastes leucostictus). For juvenile S. leucostictus, we also compared the ability of fish to defend a territory when infested with a sublethal number of gnathiids versus uninfected individuals. Uninfected fish were significantly more likely to win-pairwise contests versus infected fish. These findings suggest that gnathiids can significantly impact juvenile coral reef fish survival, and affect population dynamics well past the settlement stage.

Many species have multi-stage life cycles in which the youngest stages (e.g., larvae) are small, dispersive, and abundant, whereas later stages are sessile or sedentary. Quantifying survival throughout such early stages is critical for understanding dispersal, population dynamics, and life history evolution. However, dispersive stages can be very difficult to sample in situ, and estimates of survival through the entire duration of these stages are typically poor. Here we describe how demographic information from juveniles and adults can be used to estimate survival throughout a dispersive larval stage that was not sampled directly. Using field measurements of demography, we show that detailed information on post-settlement growth, survival, and reproduction can be used to estimate average larval survivorship under the assumption that a typical individual replaces itself over its lifetime. Applying this approach to a common coral reef fish (bicolor damselfish, Stegastes partitus), we estimated average larval survivorship to be 0.108 % (95 % CI 0.025–0.484). We next compared this demography-based estimate to an expected value derived from published estimates of larval mortality rates. Our estimate of larval survivorship for bicolor damselfish was approximately two orders of magnitude greater than what would be expected if larval mortality of this species followed the average, size-dependent pattern of mortality inferred from a published sample of marine fishes. Our results highlight the importance of understanding mortality during the earliest phases of larval life, which are typically not sampled, as well as the need to understand the details of how larval mortality scales with body size.

Predicting multiple predator effects (MPEs) on shared prey remains one of the biggest challenges in ecology. Empirical evidence indicates that interactions among predators can alter predation rates and modify any expected linear effects on prey survival. Knowledge on predator density, identity and life-history traits is expected to help predict the behavioral mechanisms that lead to non-linear changes in predation. Yet, few studies have rigorously examined the effects of predator-predator interactions on prey survival, particularly with marine vertebrate predators. Using an additive-substitutive design, we experimentally paired reef piscivores with different hunting mode [active predator, Pseudochromis fuscus (F); ambush predators, Cephalopholis boenak (B), Epinephelus maculatus (M)] to determine how behavioral interactions modified their combined impacts on damselfish prey. Results showed that behavioral patterns among predators matched those predicted from their hunting mode. However, it was the identity of the predators what determined the strength of any positive or negative interactions, and thus the nature and magnitude of MPEs on prey survival (i.e., risk-enhancing effects: treatments BB, MM and FM; risk-reducing: BM; and linear effects: FF, FB). Given the specificity of predator-predator interactions, none of the predators were fully functionally redundant. Even when two species seemed substitutable (i.e., predators F and M), they led to vastly diverse effects when paired with additional predator species (i.e., B). We concluded that knowledge of the identity of the predator species and the behavioral interactions among them is crucial to successfully predict MPEs in natural systems.

The supply of larvae is a major determinant of population and community structure in coral reef fishes. However, spatial and temporal variation in condition (i.e. quality) of potential recruits, as well as their density (i.e. quantity), may influence survival and growth of juveniles. We conducted an experiment to test whether recent feeding history could affect growth, condition and post-recruitment survival in a Caribbean damselfish, Stegastes partitus. Fish were collected soon after settlement, and fed either low or high rations in aquaria for 7 days. Fish fed the high ration grew faster in aquaria and were in a better condition (higher total lipids and Fulton’s condition factor) at the end of the feeding period. Subsequently, we released 50 fish in 25 pairs (one fish subjected to low rations, the other to high rations) on a Bahamian coral reef and monitored survival for 10 days. Survivorship of high-ration fish was double that of low-ration fish (80 vs 40% over 10 days). However, low-ration fish that survived 10 days were of similar condition and grew at similar rates to high-ration fish, suggesting that short-term ration differences may not persist in surviving fish. Laboratory experiments showed that low-ration fish were taken by piscivorous fishes before high-ration fish, indicating that differential predation may account for survival differences. This study highlights the potential of feeding history and condition to affect the relationship between patterns of larval arrival at reefs, and subsequent juvenile and adult population densities.

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.

For species with metapopulation structures, variation in abundance among patches can arise from variation in the input rate of colonists. For reef fishes, variability in larval supply frequently is invoked as a major determinant of spatial patterns. We examined the extent to which spatial variation in the amount of suitable habitat predicted variation in the abundance of the damselfish Dascyllus aruanus, an abundant planktivore that occupies live, branched coral throughout the Indo-Pacific. Reef surveys established that size, branching structure and location (proximity to sand) of the coral colonies together determined the "suitability" of microhabitats for different ontogenetic stages of D. aruanus. Once these criteria were known, patterns of habitat use were quantified within lagoons of five Pacific islands. Availability of suitable habitat generally was an excellent predictor of density, and patterns were qualitatively consistent at several spatial scales, including among different lagoons on the same island, among different islands and between the central (French Polynesia and Rarotonga) and western (Great Barrier Reef, Australia) South Pacific. A field experiment that varied the amount of suitable coral among local plots indicated that habitat for settlers accounted for almost all of the spatial variation in the number of D. aruanus that settled at that location, suggesting that spatial patterns of abundance can be established at settlement without spatial variation in larval supply. Surveys of four other species of reef-associated fish revealed that a substantial fraction of their spatial variation in density also was explained by availability of suitable reef habitat, suggesting that habitat may be a prevalent determinant of spatial patterns. The results underscore the critical need to identify accurately the resource requirements of different species and life stages when evaluating causes of spatial variation in abundance of reef fishes.

Local patterns of adult distribution in organisms that disperse young as pelagic larvae can be determined at the time of recruitment through habitat selection or, shortly thereafter, through post-recruitment processes such as differential juvenile survivorship and interspecific competition. This study addresses the importance of habitat selection by recruits in establishing the local pattern of adult distribution in two sympatric Caribbean damselfish species, Stegastes dorsopunicans and S. planifrons. Both species inhabit shallow reefs but show little overlap in their distribution; S. dorsopunicans predominates in the reef crest and S. planifrons occurs primarily on the reef slope. Furthermore, S. dorsopunicans is associated with rocky substrate, while S. planifrons occupies live coral. The substrate cover follows a similar pattern with coral being much less common on the reef crest than on the reef slope. Monitoring recruitment every other day in reciprocal removal experiments and artificial reefs indicates that the observed pattern of local adult distribution is a product of habitat selection for both species. The presence or absence of conspecifics did not influence recruitment patterns for either species. Stegastes dorsopunicans recruited primarily to shallow, rocky areas, appearing to cue on both substratum type and depth. Stegastes planifrons recruited exclusively to coral substratum independent of depth. These results indicate that local adult patterns of distribution can be explained by habitat selection at recruitment, and that substrate type and depth may be important cues.

Mutualistic symbioses are ubiquitous in nature and facilitate high biodiversity and productivity of ecosystems by enhancing the efficiency of energy and nutrient use within ecological communities. For example, small groups of fish that inhabit coral colonies in reef ecosystems potentially enhance coral growth through defense from coral predators, aeration of coral tissue and nutrient provisioning. This study examines whether the prevalence and consequences of fish-coral interactions vary among sites with different environmental conditions in a coral reef lagoon, using the humbug damselfish Dascyllus aruanus and its preferred coral host Pocillopora damicornis as a study system. Using a field experiment, we tested the site-specific effects of D. aruanus on coral growth, and show that the cost-benefit ratio for corals hosting fish varies with local environmental variation. Results of this study also demonstrate that fish prefer to inhabit coral colonies with particular branch-spacing characteristics, and that the local abundance of D. aruanus influences the proportion of coral colonies within a site that are occupied by fish rather than increasing the number of fish per colony. We also show that corals consistently benefit from hosting D. aruanus via defense from predation by corallivorous butterflyfish, regardless of local environmental conditions. These findings highlight the need to consider the potential for multiple scale- and state-dependent interaction effects when examining the ecology of fish-coral associations. We suggest that fluctuating cost-benefit ratios for species interactions may contribute to the maintenance of different colony phenotypes within coral populations.

Predators use a variety of information sources to locate potential prey, and likewise prey animals use numerous sources of information to detect and avoid becoming the meal of a potential predator. In freshwater environments, chemosensory cues often play a crucial role in such predator/prey interactions. The importance of chemosensory information to teleost fish in marine environments is not well understood. Here, we tested whether coral reef fish predators are attracted to damage-released chemical cues from already wounded prey in order to find patches of prey and minimize their own costs of obtaining food. Furthermore, we tested if these chemical cues would convey information about status of the prey. Using y-maze experiments, we found that predatory dottybacks, Pseudochromis fuscus, were more attracted to skin extracts of damselfish, Pomacentrus amboinensis, prey that were in good condition compared to prey in poor body condition. Moreover, in both the laboratory and field, we found that predators could differentiate between skin extracts from prey based on prey size, showing a greater attraction to extracts made from prey that were the appropriate size to consume. This suggests that predators are not attracted to any general substance released from an injured prey fish instead being capable of detecting and distinguishing relatively small differences in the chemical composition of the skin of their prey. These results have implications for understanding predator foraging strategies and highlights that chemical cues play a complex role in predator-prey interactions in marine fish.

Phenotypic variability within cohorts of juvenile organisms can serve as the basis for selective mortality. Previous studies have demonstrated the important role that predators play in this process but not the impact of competitors on selective predation. We use a combination of lab and field studies to evaluate the effect of the presence of adult competitor damselfish (Dascyllus aruanus and Pomacentrus moluccensis; family Pomacentridae) on the selective mortality of newly-arrived (settled) lemon damselfish (P. moluccensis) by resident predator fishes (Pseudochromis fuscus Pseudochromidae and Cheilodipterus quinquelineatus Apogonidae). Lab trials consisted of mesocosm experiments in which the behaviour, mortality, and physiological condition (measured as lipid content) of surviving P. moluccensis settlers from each of three treatments: (1) predators absent, (2) predators present, and (3) predators and competitors present, were compared. The field study involved stocking newly settled P. moluccensis on natural bommies (patch reefs) which had either been subject to a partial removal of resident fish (predators and competitors) or left alone. Results indicated there was very strong condition-based selective mortality in both the lab and field trials. In both cases there was a strong positive relationship between mortality and the lipid content of surviving fish; implying low-condition fish were selectively removed. The mesocosm trials indicated that the strength of mortality as well as condition selectivity was higher when competitors were present than when they were absent. Behavioural observations in the mesocosm study suggest that attention by juvenile P. moluccensis to the movements and occasional chases of the competitors (especially D. aruanus) reduced their vigilance to the predators. These results suggest the important and interactive roles which condition of newly settled reef fish and interspecific competition can play in the outcomes of post-settlement predation.

Selective mortality within a population, based on the phenotype of individuals, is the foundation of the theory of natural selection. We examined temperature-induced shifts in the relationships among early life history traits and survivorship over the embryonic and larval stages of a tropical damselfish, Pomacentrus amboinensis. Our experiments show that temperature determines the intensity of selective mortality, and that this changes with ontogeny. The size of energy stores determined survival through to hatching, after which egg size became a good indicator of fitness as predicted by theoretical models. Yet, the benefits associated with egg size were not uniform among test temperatures. Initial egg size positively influenced larval survival at control temperature (29 degrees C). However, this embryonic trait had no effect on post-hatching longevity of individuals reared at the higher (31 degrees C) and lower (25 degrees C) end of the temperature range. Overall, our findings indicate that the outcome of selective mortality is strongly dependent on the interaction between environment conditions and intrinsic developmental schedules.

The evolution of different colour morphs and how they are maintained in animal populations is poorly understood. We investigated the mechanisms maintaining yellow and brown morphs of a coral-reef fish, Pseudochromis fuscus, at Lizard Island, on the Great Barrier Reef. Histological examination of the gonads revealed that colour morphs were not sex-limited, therefore sexual selection does not appear to promote dichromatism in this species. The field distributions of the two colour morphs were spatially segregated, limiting the opportunity for negative frequency-dependent selection to operate. Our results support another ecological mechanism of coexistence. The yellow morph occurred in deeper areas, usually close to the reef edge, where there was a proportionally high cover of live branching corals. In contrast, the brown morph occurred in shallower areas, more distant from the reef edge, that were proportionally low in live branching corals. Within these habitats, each colour morph of P. fuscus displayed a close association with similar coloured damselfishes from the genus Pomacentrus. The yellow morph was associated with predominantly yellow damselfishes (P. moluccensis and P. amboinensis) and the brown morph with darker coloured species (P. adelus and P. chrysurus). Multiple-choice experiments in the laboratory revealed that: (1) each colour morph of P. fuscus preferentially selected habitat patches occupied by damselfishes with the same colouration; and (2) differences in microhabitat use between the two colour morphs of P. fuscus were due to the presence of different coloured damselfishes in these microhabitats. P. fuscus is a predator of newly recruited damselfishes and the striking resemblance between each morph of P. fuscus and the damselfish with which it was associated, suggests that aggressive mimicry may promote coexistence of P. fuscus colour morphs.

Local abundance and dynamics of sedentary species with a dispersing life stage reflect factors that influence input and loss rates to patches of suitable habitat. For reef fishes, more attention has focused on sources of variation in input (larval settlement) than on patterns and causes of subsequent losses. We estimated spatial and temporal variation in juvenile mortality of a tropical damselfish, yellow-tail dascyllus (Dascyllus flavicaudus; Pomacentridae), using a fixed density experiment that was repeated 5 times at the same eight mid-lagoon localities at Moorea, French Polynesia. There was little temporal variation in the overall percent of outplanted fish lost in 48 h among five time periods (range: 32-37%), whereas there was substantial variation among the sites in the average percent lost (range: 16-56%). Differences in loss rates among the sites were highly consistent among the time periods. Densities of predators of juvenile dascyllus varied substantially among the eight sites and were highly correlated with loss rate of dascyllus. We used the empirically derived relationship between predator density and damselfish loss rate to predict the loss rate of dascyllus at four additional sites, and there was excellent agreement between the predicted and observed loss rates. There was a strong positive relationship between predator densities at the 12 sites and structural attributes of the reefs that do not change on a fast time scale, suggesting why there was strong spatial and weak temporal variation in mortality rates, with no interaction between spatial and temporal variation. Natural settlement rates of yellow-tail dascyllus and of a close congener (humbug dascyllus, D. aruanus) varied among the sites, and settlement of the two species was inversely correlated (r=-0.68). Settlement of these species was not statistically correlated with variation in mortality rate, but there was a weak trend for settlement of yellow-tail dascyllus to be greater at sites with higher mortality (r=0.27), and for settlement of humbug dascyllus to be greater at sites with lower mortality (r=-0.32). We calculated that even these weak co-variances could reduce (yellow-tail dascyllus) or increase (humbug dascyllus) the spatial variance in density of 48-h-old recruits arising at settlement by 19 and 27% respectively. Taken together, the findings suggest that the interactions between and relative contributions of input and loss processes can differ substantially over a scale of a few kilometers, resulting in a mosaic of local patches characterized by different abundances and dynamics.

Replenishment of local populations of reef fishes typically occurs via settlement of planktonic larvae, a process that is variable in space and time. We examined spatial variation in settlement of three species of damselfishes (genus Dascyllus) in relation to variation in average near-field current speed. Although the larvae of these species colonized at the same times, they repeatedly exhibited qualitatively different spatial patterns of settlement in the lagoons of Moorea, French Polynesia. Each damselfish had a unique, temporally consistent pattern of variation in settlement relative to among-site variation in near-field flow speed. At the speeds encountered, settlement was related linearly to increasing average current flow for yellow-tail dascyllus (D. flavicaudus), was a positive but decelerating function for humbug dascyllus (D. aruanus) and was a hump-shaped function for three-spot dascyllus (D. trimaculatus). Such qualitatively different relationships could arise if variation in current speed affected an individual's probability of settling differently among the species. The generalized relationships between flow speed and settlement of these species predicted well the pattern of covariation in settlement of these species among new sites where the availability of suitable habitat was standardized. These findings imply that differences in larval abilities in the near-field can result in distinctly different patterns of larval colonization among species, even in the absence of any other source of variation.

Maternal hormones can play an important role in the development of fish larvae. Levels of the stress hormone, cortisol, in females are elevated by social interactions and transferred directly to the yolk of eggs, where they may influence developmental rates. In some vertebrates, prenatal exposure to high levels of testosterone determine early growth rates, social status and reproductive success. The present study examined whether post-fertilization exposure of eggs of the tropical damselfish, Pomacentrus amboinensis (Pomacentridae), to natural levels of cortisol or testosterone directly affects larval morphology at hatching. Maternal and egg levels of cortisol and testosterone varied widely among clutches of eggs from local populations around Lizard Island on the Great Barrier Reef. The morphology of larvae produced by these local fish populations also varied widely and differed significantly among sites (e.g., standard length: 2.6–3.4 mm; yolk sac area: 0.01–0.13 × 10−2 mm2). Laboratory experiments showed that elevated cortisol levels in the egg reduced larval length at hatching, while slight elevations in testosterone increased yolk sac size. The influence of testosterone, and to a smaller extent cortisol, on larval morphology differed among egg clutches. These differences were partly explained by differences in initial egg hormone levels. Morphological changes induced by experimental hormonal regimes encompassed the entire range of variability in body attributes found in field populations. It is unclear whether cortisol influences growth alone or development rate or both. Testosterone appears to influence yolk utilization rates, and has no significant effect on growth, in contrast to its role in later developmental stages. Maternally derived cortisol and testosterone are important in regulating growth, development, and nutritive reserves of the embryo and larvae of this fish species. Factors that influence the maternal levels of cortisol and testosterone may have a major impact on larval mortality schedules and, therefore, on which breeding individuals contribute to the next generation.

Spatial patterns of settlement and abundance of older life stages were examined for three species of damselfish in the genus Dascyllus by monitoring natural colonization of standard amounts of initially empty juvenile microhabitat (anemones for D. trimaculatus; branching coral for D. flavicaudus and D. aruanus) transplanted to a series of sites within lagoons of Moorea, French Polynesia. Large spatial differences in larval colonization were observed, which were temporally consistent but different among the species. At the whole-island scale, D. trimaculatus settled primarily on the northern shore, while settlement of the other two species was greatest at the southern end. The three species also showed different patterns of settlement within lagoons: D. aruanus settled mainly nearer to shore, D. flavicaudus primarily on offshore lagoon portions and D. trimaculatus colonized equally across the lagoons. Among sites around the island, the relative abundance of older juveniles after 10 months was a curvilinear function of the relative abundance of settlers for two species (D. trimaculatus and D. flavicaudus). There was no relationship between patterns of settlement and abundance of older juveniles for D. aruanus, although juvenile abundance was inversely related to that of juvenile D. flavicaudus. At the within-lagoon scale, settlement mirrored almost exactly the relative abundance of older lifestages of D. trimaculatus and D. flavicaudus, whereas there was just a qualitative match for D. aruanus. A competition experiment revealed that juvenile D. flavicaudus had a greater effect on population growth of D. aruanus than vice versa, and this mechanism helped explain why the modification of settlement patterns was greatest in D. aruanus. Interspecific variation in abundance of older stages was shaped to differing extents by both patterns of larval delivery and subsequent density-dependent processes involving competition for shelter space.

Wave-driven water flow is a major force structuring marine communities. Species distributions are partly determined by the ability to cope with variation in water flow, such as differences in the assemblage of fish species found in a given water flow environment being linked to swimming ability (based on fin shape and mode of locomotion). It remains unclear, however, whether similar assembly rules apply within a species. Here we show phenotypic variation among sites in traits functionally linked to swimming ability in the damselfish Acanthochromis polyacanthus. These sites differ in wave energy and the observed patterns of phenotypic differences within A. polyacanthus closely mirrored those seen at the interspecific level. Fish from high-exposure sites had more tapered fins and higher maximum metabolic rates than conspecifics from sheltered sites. This translates to a 36 % larger aerobic scope and 33 % faster critical swimming speed for fish from exposed sites. Our results suggest that functional relationships among swimming phenotypes and water flow not only structure species assemblages, but can also shape patterns of phenotypic divergence within species. Close links between locomotor phenotype and local water flow conditions appear to be important for species distributions as well as phenotypic divergence across environmental gradients.

Populations of fishes on coral reefs are replenished by the settlement of pelagic larvae to demersal populations. Recruitment varies spatially and temporally and can exert strong effects on the dynamics of reef fish populations. This study examined the effect of microhabitat characteristics on small-scale and large-scale recruitment variation in the three-spot damselfish, Stegastes planifrons (Cuvier). Comparison of 0.25-m2 quadrats occupied by three-spots with randomly sampled null quadrats showed that three-spots quadrats contained a higher percent cover of the coral Montastrea annularis than would be expected at random. Manipulative experiments on three types of 1.0-m2 patch reefs (living M. annularis, dead Porites Porites and dead Acropora palmata) patch reefs on showed that this non-random distribution was established by microhabitat choice during settlement and not by differential post-settlement survival. The presence of conspecific juveniles did not affect settlement. Recruitment was monitored at nine sites on three islands over 3 years. Recruitment showed no consistent pattern in the relative levels of recruitment among sites. Similarly, no consistent relationship emerged between recruitment levels and microhabitat characteristics at the nine sites. For example, at this large scale, the percent cover of M. annularis explained variation in recruitment in only 1 out of 3 years. These results suggest that small-scale recruitment patterns are influenced by microhabitat choice during settlement, but that these habitat effects do not scale up to influence large-scale variation in recruitment.

On many Caribbean fringing coral reefs, two closely related and ecologically similar damselfishes, the beaugregory (Stegastes leucostictus Müller and Troschel) and the cocoa damselfish (S. variabilis Castelnau), occupy nonoverlapping vertical distributions. In St. Croix (USVI), beaugregory are very abundant in shallow water back reef habitats (1-2 m depth) while cocoa damselfish are restricted to the base of the forereef (10-15 m depth).In this study, the roles of habitat selection at settlement and juvenile persistence were investigated to determine their influence on this pattern of zonation. Settlement events observed at intervals over a two-year period revealed that habitat selection occurred at settlement and was confined to habitats occupied by adults. In addition, differences in juvenile persistence (due to mortality and/or emigration) were found when species were translocated between depths. Over a period of 100-days, juvenile beaugregory moved from 1 m to 12 m depth suffered four-fold greater losses at the deeper sites than shallow water controls, while translocated cocoa damselfish suffered twice as many losses in shallow water than controls at 12 m depth. Despite these differences in persistence, growth rates of the two species were similar and independent of depth. These results indicate that preferential habitat selection at settlement, perhaps an evolutionary response to differential juvenile mortality, may play a deciding role in determining distributions of ecologically similar species of coral reef fishes.

For species with complex life cycles, variation in growth or condition during early life stages may affect survival in later stages or during important life-stage transitions. These effects on survival may be an important source of recruitment variability. However, survival during early stages is often density-dependent and it is unclear how the effects of early condition on recruitment compare to the effects of density alone. In this study, I investigated both the independent and interactive effects of condition and density on post-settlement survival and growth of bicolor damselfish (Stegastes partitus). In a field experiment, I crossed two levels of population density with two levels of condition (established by laboratory feeding of recent settlers) and measured growth and survivorship over a 30-day period. Low condition and high density both decreased survivorship. However, the effects of density were stronger and the effects of condition and density on survivorship were independent. In contrast, condition and density had interactive effects on growth in that density reduced growth only in the high-condition treatments. In a second experiment, I examined how condition and density affected intraspecific aggression and shelter use, two behaviors that may influence growth and survival. Shelter use was unaffected by density and condition. The rate of intraspecific chases was greater and increased more strongly with density when fish were in higher condition. Average growth rate of fish decreased with increasing rate of intraspecific chases, suggesting that the difference in aggression between condition levels was the mechanism leading to differences in density-dependent growth. These results suggest that variation in condition at settlement can significantly contribute to variation in population abundance, despite density dependence in survival. However, because behaviors that affect density-dependent growth can be altered by condition at settlement, the degree to which population biomass is regulated may depend on initial condition.

Herbivorous fishes have been attributed a central role in structuring benthic communities on coral reefs. However, the relative importance of different behavioural groups of herbivores may differ and their interactions may be complex. This study focuses on an experiment that discriminates between two groups of herbivorous fish: (1) “Foragers” (relatively mobile, schooling grazers, including parrotfishes and surgeonfishes) and (2) “Farmers” (highly site-attached, territorial species, primarily damselfishes). Preliminary observations at Kimbe Bay (Papua New Guinea) showed that both groups were common, and that farmers defended areas from foragers and maintained algal communities that were distinct from the surrounding undefended substratum. An orthogonal combination of a farmer removal treatment and a forager exclusion treatment was applied to isolate their separate effects on algae and corals, and to determine whether farmer territory composition results from forager exclusion or algal cultivation. The experiment showed that foragers had quantitatively greater and qualitatively different effects on sessile benthic community structure than farmers. Where foragers were excluded, there were substantial increases in the cover and biomass of macro-algae and a decline in some corals, regardless of the presence of farmers. Where farmers were removed there was a moderate decline in the cover of some food algal species, regardless of whether foragers had access. No effect of the exclusion of foragers by farmers could be detected. Our results support prevailing views that foragers have a major impact on coral reefs and farmers cultivate selected algae, but challenge the hypothesis that damselfish influence habitat structure by moderating forager disturbance.

The synchronized spawning of corals in many parts of the Indo-Pacific represents a huge injection of biological material into the waters around reefs. Much of this material is consumed by fishes and filter-feeding invertebrates in the 5 or so days following spawning. The present study is the first to document the effect of the consumption of coral propagules on a population of facultatively planktivorous fish and the transference of physiological condition across generations. The study compares two populations of the damselfish Pomacentrus amboinensis that fed to differing degrees on coral propagules for 5 days after the annual mass spawning of corals at Lizard Island, Great Barrier Reef, Australia. Wind blew coral slicks over the outer lagoon to the inner lagoon some 1.5 km away. While coral propagules were abundant in the water column in the windward location, they were scarce by the time the water mass reached the inner lagoon. Behavioral observations 2-5 days after coral spawning showed that a significantly higher proportion of P. amboinensis was feeding on coral propagules in the windward location than in the inner lagoon location. Windward location females consumed coral propagules almost exclusively and had fuller guts than females from the inner lagoonal location. Five days after the mass coral spawning, windward location females had a higher condition factor and a larger liver mass relative to body mass compared to females within the inner lagoon or females from both locations 2 months later. Fish eggs laid by the windward location females soon after coral spawning yielded larvae that had 25% larger yolk sacs and 100% larger oil globules than did larvae produced from the females from the inner lagoon location, or larvae produced at either location prior to or well after coral spawning in 2 previous years. Larger yolk sacs and oil globules have been shown to have direct survival benefits in the transition from endogenous to exogenous feeding. A feeding experiment conducted on patch reefs showed that diet supplementation of breeding females with a high lipid food for just 5 min per day was sufficient to significantly increase yolk-sac sizes of newly hatched larvae. Evidence suggests that females gain a fitness advantage from feeding on coral spawn and that this is passed on to their offspring.

Coral reef fishes, like many marine organisms, have a complex life history that consists of a planktonic larvae stage and a benthic juvenile or adult stage. We used the growth records in the otoliths of a common damselfish to investigate the extent to which processes in the plankton determined the outcome of events after benthic settlement. Sequential samples of the same cohort showed that individuals that survived intense selective mortality 1–3 months after settlement were those fish that were the larger members of the cohort at hatching and grew faster during planktonic life. Such links between life history phases are likely to occur in reef fishes whenever there is selection for a trait that is cumulative, such as size. They may not only operate between life history stages in the same individuals, but even between those of different generations via maternal effects on size at hatching.

Populations with dispersive larvae are often demographically open such that local reproduction and subsequent larval settlement are not linked. Thus, understanding whether and how settlement patterns are established and subsequently modified is central to understanding local demography. Settlement is typically not measured directly, but rather it is estimated by recruitment, which is the observation of new individuals sometime after settlement. At Lizard Island on the Great Barrier Reef, I examined how patterns of recruitment of coral-reef fishes were modified across a range of natural recruit densities in the presence and absence of resident predators. Resident predators decreased recruitment and increased mortality for all species, but these effects varied considerably among species. The effects of predators on recruitment were at least partly due to mortality within 2 days after settlement. At their most extreme, predators caused recruitment failure of several species of butterflyfish. For one species of damselfish (Pomacentrus amboinensis), predators both induced weakly density-dependent mortality and obscured any relationship between recruitment and subsequent abundance, while for another damselfish (Neopomacentrus cyanomos), mortality was density-independent and subsequent abundance was a function of recruitment. These contrasting results may reflect differences in prey behavior. P. amboinensis tended to feed near or within the branches of coral inhabited by resident predators, while N. cyanomos tended to feed higher in the water column above the reefs, and thus farther away from resident predators. These results highlight the speed and extent to which patterns of settlement are modified, indicating that caution should be exercised when attributing patterns of recruitment to patterns of settlement. Tremendous between-species variation in how patterns of recruitment, and presumably settlement, were modified by predation indicates that generalizations or between-species extrapolations about the magnitude of these effects may be unwarranted.

Samples of the staghorn coral Acropora were taken from within territories defende by damselfish (Pisces: Pomacentridae) and from undefended areas. The fish utilized in this experiment were Hemiglyphidodon plagiometopon Bleeker and Pomacentrus bankanensis Bleeker. The extent of bioerosion was determined by randomly selecting pieces of coral substrate from treatment and control areas, cutting transverse sections, and determining total eroded area with the aid of enlarged photographs. Boreholes within the photos were traced with a digitizing sensor and area was integrated with the aid of a computer.Corals inside territoties were significantly more bioeroded (p0.001) than corals outside areas. Most of the destruction was caused by boring sponges (Cliona sp.) and sipunculids (Cleosiphon). It is suggested that bioerosion is accelerated within territories as a result of reduction in grazing by fish.

Interference behavior by threespot damselfish directed at the sea urchins, Diadema antillarum and Echinometra viridis, differed in levels of aggression and discrimination. Higher aggression towards and recognition of Diadema by threespots was correlated with the distribution of Diadema along edges of coral patches. Lower aggression levels combined with lower recognition levels of Echinometra were correlated with a distribution of Echinometra closer to damselfish algal lawns. Differences in behavior of the urchins stimulated differing levels of aggression by the damselfish directly affecting the distribution of the urchins in the back-reef environment.

Species that shelter in a biogenic habitat can influence their refugia and, in turn, play an essential role in shaping local patterns of biodiversity. Here we explore a positive feedback loop between the provisioning rate of habitat-forming branching corals and their associated fishes and show how interactions between two groups of fish--the planktivorous damselfish and predatory hawkfish--altered the feedback. A field experiment confirmed that skeletal growth of branching coral (genus Pocillopora) increased substantially with increasing numbers (biomass) of resident fishes, likely because they greatly increased the interstitial concentrations of nutrients. Because there is a positive relationship between colony size and number (biomass) of associated fishes (primarily damselfishes in the Family Pomacentridae), a structure-function feedback loop exists in which increasing numbers of damselfish enhance coral growth and larger corals host greater abundances (and species richness) of fish. However, interactions between damselfishes and arc-eye hawkfish, Paracirrhites arcatus, a largely solitary resident, can disrupt this positive feedback loop. Field surveys revealed a marked pattern of fish occupancy related to coral size: Pocillopora colonies of sufficient size to host fish (40 cm circumference) had either groups of damselfish or an arc-eye hawkfish; only larger colonies (75 cm) were occupied by both the damselfish and hawkfish. Subsequent short- and long-term experiments revealed that on intermediate-sized Pocillopora colonies, arc-eye hawkfish prevented the establishment of damselfish by suppressing their recruitment. The demographic consequences to the host coral were substantial; in a 1-year-long experiment, intermediate-size Pocillopora occupied by hawkfish grew at half the rate of corals that hosted groups of damselfish. These findings indicate that: (1) species which occupy a biogenic habitat can enhance the provisioning rate of their habitat; (2) such positive feedbacks between community structure and ecosystem function can be disrupted by a strong interactor; (3) even substantial consequences on ecosystem processes that arise can be difficult to discern.

Three adult size classes of the territorial Caribbean dusky damselfish,Stegastes dorsopunicans, are differently distributed with respect to habitat, and with respect to the biomass of filamentous algal turfs in the areas they defend. The density of large individuals is positively correlated with the decalcified dry biomass of these turfs, whereas the densities of medium and small individuals are inversely related to algal biomass. Density of the urchin,Diadema, is also inversely correlated with algal biomass. The high density of large dusky damselfish in sites with algal turfs of relatively high biomass probably results from preferences of dusky damselfish for sites in which algal turfs are thick, and superior abilities of large individuals to defend these sites. Because both rate of attacks and the effectiveness of attacks on territory invaders by dusky damselfish increases with increasing size, sites with relatively high biomass algal turfs are typically better defended than those with lower biomass turfs. Apparently as a result of this, small foraging groups of the blue tang surgeonfish,Acanthurus coeruleus, feed less on high biomass algal turfs than do larger foraging groups, the members of which experience attacks by defending damselfishes less frequently. The relatively low proportionate use of high biomass feeding sites by solitary blue tangs and members of small foraging groups is caused by dusky damselfish. When the density of this damselfish was reduced artificially, use of high biomass algal turfs by solitary blue tangs increased to a level indistinguishable from that of participants in large foraging groups.