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Spatial variation in microhabitats, predation pressure, and competitor assemblages may create a landscape of selection pressures that drives spatial variation in phenotypes. Coral reef ecosystems provide a wide range of environmental variability and therefore an excellent opportunity to quantify and explore the potential effects of fitness landscapes on phenotypes of reef fish that inhabit these ecosystems. I evaluate patterns of variation in phenotypic traits of a common coral reef fish (Thalassoma hardwicke) across a prominent environmental gradient (from offshore to inshore within a lagoon system). I quantify phenotype-environment gradients established for cohorts of fish soon after their settlement, and how these relationships change through the time to infer selection gradients (Chapter 2). Specifically, I estimate the strength of selection on a set of early life-history traits estimated from otoliths (i.e., larval growth rates and pelagic larval duration), and morphological features (i.e., body condition and fin size). Building on the results of Chapter 2, I conduct an observational field study to estimate the behavioural consequences of spatial variation in early life history traits for young T. hardwicke (Chapter 3). I quantify feeding frequency and agonistic interactions between young T. hardwicke and intra- and interspecific competitors, and evaluate these as a function of growth history traits. Growth history traits correlate positively with the frequency and direction of agonistic interactions. Species identity (i.e., which species were interacting with young T. hardwicke) is also important for determining the frequency and direction of agonistic interactions. Additionally, the size difference between T. hardwicke and the competitor also influenced the frequency and direction of agonistic interactions. I use laboratory experiments to better understand the role of conspecifics on settlement choice of young T. hardwicke (Chapter 4). I evaluate the influence of growth histories on settlement choice in a laboratory experiment. Growth history does not significantly influence habitat choice with regards to conspecific presence for newly settled T. hardwicke. Additionally, fish that avoided habitats with conspecifics took longer to make a settlement choice, which may suggest that neophobic fish may choose habitats without conspecifics possibly to avoid competition.I then use field experiments to evaluate the role of conspecifics on post-settlement survival of young T. hardwicke (Chapter 4), focusing on the role of conspecific size-differences and priority effects. I pair newly settled fish with larger conspecifics to evaluate the role of size-differences and priority effects on 1) frequency of agonistic interactions, and 2) post-settlement survival of newly settled T. hardwicke. I find no significant differences in either frequency of agonistic interactions or post-settlement survival.The presence of phenotype-environment gradients in this system provides an excellent opportunity to test for phenotype-environment mismatches in young T. hardwicke in different environments. I set up a reciprocal transplant experiment in the field (Chapter 5) by comparing growth and survival of ‘control’ fish (i.e., fish remaining in their original environments) to that of ‘transplant’ fish (i.e., fish transplanted to a new environment). Transplant fish experience a significant reduction in survival, which suggests that phenotype-environment mismatch may be present in this system. I also found spatial differences in growth rates for treatment fish, suggesting the cost of phenotype-environment mismatches are context-dependent. Overall, the observational and experimental components of my thesis suggest that patterns of settlement and subsequent post-settlement fitness are influenced by the interface between phenotypes and environment. I find significant spatial variation in phenotypes of newly settled T. hardwicke, and post-settlement survival is also spatially variable. Additionally, disrupting the established phenotype-environment gradients alters growth patterns and increases mortality. These results highlight the importance of context-dependence in understanding patterns of settlement and survival for young reef fish and illustrate the various roles of ecological processes that shape phenotypic distributions within ecosystems.

Growth and survival of larval fishes is highly variable and unpredictable. Our limited understanding of this variation constrains our ability to forecast population dynamics and effectively manage fisheries. Here we show that daily growth rates of a coral reef fish (the sixbar wrasse, Thalassoma hardwicke ) are strongly lunar-periodic and predicted by the timing of nocturnal brightness: growth was maximized when the first half of the night was dark and the second half of the night was bright. Cloud cover that obscured moonlight facilitated a ‘natural experiment’, and confirmed the effect of moonlight on growth. We suggest that lunar-periodic growth may be attributable to light-mediated suppression of diel vertical migrations of predators and prey. Accounting for such effects will improve our capacity to predict the future dynamics of marine populations, especially in response to climate-driven changes in nocturnal cloud cover and intensification of artificial light, which could lead to population declines by reducing larval survival and growth.

© 2017 by the Ecological Society of America Parents are expected to make decisions about reproductive timing and investment that maximize their own fitness, even if this does not maximize the fitness of each individual offspring. When offspring survival is uncertain, selection typically favors iteroparity, which means that offspring born at some times can be disadvantaged, while others get lucky. The eventual fate of offspring may be further modified by their own decisions. Are fates of offspring set by birthdates (i.e., determined by parents), or can offspring improve upon the cards they've been dealt? If so, do we see adaptive plasticity in the developmental timing of offspring? We evaluate these questions for a coral reef fish (the sixbar wrasse, Thalassoma hardwicke) that is characterized by extreme iteroparity and flexible larval development. Specifically, we monitored larval settlement to 192 small reefs over 11 lunar months and found that most fish settled during new moons of a lunar cycle (consistent with preferential settlement on dark nights). Settlement was significantly lower than expected by chance during the full moon and last quarter of the lunar cycle (consistent with avoidance of bright nights). Survival after settlement was greatest for fish that settled during times of decreasing lunar illumination (from last quarter to new moon). Fish that settled on the last quarter of the lunar cycle were ~10% larger than fish that settled during other periods, suggesting larvae delay settlement to avoid the full moon. These results are consistent with a numerical model that predicts plasticity in larval development time that enables avoidance of settlement during bright periods. Collectively, our results suggest that fish with inauspicious birthdates may alter their developmental trajectories to settle at better times. We speculate that such interactions between parent and offspring strategies may reinforce the evolution of extreme iteroparity and drive population dynamics, by increasing the survival of offspring born at the “wrong” time by allowing them to avoid the riskiest times of settlement.

Most organisms reproduce in a dynamic environment, and life-history theory predicts that this can favor the evolution of strategies that capitalize on good times and avoid bad times. When offspring experience these environmental changes, fitness can depend strongly upon environmental conditions at birth and at later life stages. Consequently, fitness will be influenced by the reproductive decisions of parents (i.e., birth date effects) and developmental decisions (e.g., adaptive plasticity) of their offspring. We explored the consequences of these decisions using a highly iteroparous coral reef fish (the sixbar wrasse, Thalassoma hardwicke) and in a system where both parental and offspring environments vary with the lunar cycle. We tested the hypotheses that (1) reproductive patterns and offspring survival vary across the lunar cycle and (2) offspring exhibit adaptive plasticity in development time. We evaluated temporal variation in egg production from February to June 2017, and corresponding larval developmental histories (inferred from otolith microstructure) of successful settlers and surviving juveniles that were spawned during that same period. We documented lunar-cyclic variation in egg production (most eggs were spawned at the new moon). This pattern was at odds with the distribution of birth dates of settlers and surviving juveniles-most individuals that successfully survived to settlement and older stages were born during the full moon. Consequently, the probability of survival across the larval stage was greatest for offspring born close to the full moon, when egg production was at its lowest. Offspring also exhibited plasticity in developmental duration, adjusting their age at settlement to settle during darker portions of the lunar cycle than expected given their birth date. Offspring born near the new moon tended to be older and larger at settlement, and these traits conveyed a strong fitness advantage (i.e., a carryover effect) through to adulthood. We speculate that these effects (1) are shaped by a dynamic landscape of risk and reward determined by moonlight, which differentially influences adults and offspring, and (2) can explain the evolution of extreme iteroparity in sixbars.

Thalassoma hardwicke (Bennett 1830) —Sixbar wrasse Status at New Ireland. First recorded from New Ireland as Julis dorsalis by Peters (1877: 843); subsequently reported from Kavieng as Thalassoma schwanefeldi by Kailola (1975: 192). KFRS material. Specimens photographed at St. KVG18 (south side of Bauddisson Island, Kavieng District) by Serge Andréfouët on 18 Aug. 2014, and at St. KVGPMT50 (southeast of New Hanover) by Serge Andréfouët on 24 Aug. 2014. Distribution and habitat. New Ireland: 1, 2.—General distribution: South and East Africa, Madagascar and Mascarenes east to Wake and Tuamotu islands, north to southern Japan and Ogasawara Islands, south to Lord Howe, Norfolk and Austral islands. Found in small groups on coral reefs, 0–15 m depth. Marine., Published as part of Andréfouët, Serge, Chen, Wei-Jen, Kinch, Jeff, Mana, Ralph, Russell, Barry C., Tully, Dean & White, William T., 2019, Checklist of the marine and estuarine fishes of New Ireland Province, Papua New Guinea, western Pacific Ocean, with 810 new records, pp. 1-360 in Zootaxa 4588 (1) on page 239, DOI: 10.11646/zootaxa.4588.1.1, http://zenodo.org/record/2988163, {"references":["Peters, W. C. H. (1877) Ubersicht der wahrend der von 1874 bis 1876 unter der Commando des Hrn. Capitan z. S. Freiherrn von Schleinitz ausgefuhrten Reise S. M. S. Gazelle gesammelten und von der Kaiserlichen Admiralitat der Koniglichen Akademie der Wissenschaften ubersandten Fische. Monatsberichte der Koniglichen Preuss [ischen] Akademie der Wissenschaften zu Berlin, 1876, 831 - 854.","Kailola, P. J. (1975) A catalogue of the fish reference collection at the Kanudi Fisheries Research Laboratory, Port Moresby. Department of Agriculture, Stock & Fisheries, Port Moresby, Research Bulletin, 16, 1 - 277."]}

Structural refuge and competition can influence the survival of coral reef fishes; however, the effect of structural refuge on the outcome of competition remains unclear. In Moorea, French Polynesia, surveys were used to quantify habitat association for juvenile Thalassoma hardwicke and 7 sympatric labroid species. Having identified the 3 species most similar to focal T. hardwicke in habitat association, a field assay was used to determine if the presence of larger individuals of these species adversely affected the survival of focal individuals. Finally, a field experiment was used to test how competition with larger residents and structural refuge interact to influence survival of transplanted T. hardwicke. Surveys demonstrated that Gomphosus varius, Pseudocheilinus hexataenia, and T. quinquevittatum were most similar to T. hardwicke in habitat association. In the field assay, the presence of T. quinquevittatum had the greatest negative effect on survival of T. hardwicke. The field experiment revealed that competition with T. quinquevittatum and structural refuge both altered T. hardwicke survival, although their effects were not interactive. Survival of T. hardwicke was 2.3 times greater in treatments without T. quinquevittatum relative to those with T. quinquevittatum, and 2.8 times greater in treatments with structural refuge relative to those without structural refuge. The additive effect may have occurred via the establishment of social dominance hierarchies between transplanted T. hardwicke and resident T. quinquevittatum independently of structural refuge, suggesting that it is important to account for interactions occurring independently of resources when examining resource competition.

The importance and strength of density dependence continues to engender debate because of its central importance to population dynamics and regulation. Here, we show how confounding effects of site quality can mask strong effects of density dependence. In particular, we explore spatiotemporal variation and covariation among (1) densities of newly settled coral reef fish (Thalassoma hardwicke), (2) environmental characteristics, and (3) the strength of density-dependent mortality. Environmental features of patch reefs were spatially and temporally variable and influenced density-dependent survival. Higher- quality sites (i.e., reefs possessing features that yield greater numbers of recruits at any given settlement level) received greater settlement, and this relationship masked the op- eration of density dependence when variation in quality among sites (or times) was not distinguished (a common approach in many observational studies of density dependence). Our work illustrates how spatiotemporal covariation in settlement density and site quality can obscure patterns of density dependence at larger scales, contributing to a phenomenon we call ''cryptic density dependence.'' Acknowledging patterns and consequences of co- variance may alter the way we study population dynamics, especially of marine organisms, where the link between processes that affect settlement and post-settlement survival remains relatively poorly understood.

Multiple processes typically influence patterns of abundance. Despite this widely accepted view, many studies continue to approach ecological questions from a single-factor, or, at most, a two-factor perspective. Here, I evaluate the consequences of considering, separately and jointly, the effects of three factors (larval settlement, reef resources, and postsettlement losses) on spatial patterns of abundance of a marine reef fish, the six bar wrasse (Thalassoma hardwicke). Using correlational methods commonly employed in single-factor studies, I show that local patterns of abundance of juvenile wrasse could be attributed entirely to either (1) patterns of abundance of settlement habitat, or (2) patterns of larval settlement. This result occurred because habitat and presumed larval delivery covaried in space. I manipulated abundance of settlement habitat in a field experiment to uncouple this covariation and found subsequent settlement to be simultaneously influenced by both factors. However, joint effects of habitat and settlement failed to account for patterns of abundance of juvenile wrasse without also considering a third factor - postsettlement losses - which were density-dependent and substantially modified patterns of settlement. These results illustrate (1) how multifactorial explanations may be falsely refuted when incomplete sets of multiple factors are considered, and (2) how single-factor explanations may misrepresent underlying multifactorial causation of ecological patterns. Uncovering the interactive role of multiple factors in determining ecological patterns of interest requires a shift from single-factor approaches to more pluralistic perspectives.

Multiple processes can act together to determine abundance of organisms and structure of communities. Recently, appreciation of this fact has motivated development of conceptual and statistical frameworks that quantitatively assess the relative importance of multiple causal factors. However, little consideration has been given to variability in the "importance" of processes through space and time (i.e. robustness), which represents another facet of a process's importance. Here, I focused on populations of a coral reef fish (Thalassoma hardwicke) and used an existing analytical method to assess the relative importance of initial population inputs (larval supply) and subsequent juvenile mortality in determining the average abundances of juvenile fish populations in different locations and times. The relative importance of processes varied significantly both temporally and spatially across a range of scales, and indicate a need for future assessments of relative importance to incorporate this variability.

Many communities experience repeated periods of colonization due to seasonally regenerating habitats or pulsed arrival of young-of-year. When an individual's persistence in a community depends upon the strength of competitive interactions, changes in the timing of arrival relative to the arrival of a competitor can modify competitive strength and, ultimately, establishment in the community. We investigated whether the strength of intracohort competitive interactions between recent settlers of the reef fishes Thalassoma hardwicke and T. quinquevittatum are dependent on the sequence and temporal separation of their arrival into communities. To achieve this, we manipulated the sequence and timing of arrival of each species onto experimental patch reefs by simulating settlement pulses and monitoring survival and aggressive interactions. Both species survived best in the absence of competitors, but when competitors were present, they did best when they arrived at the same time. Survival declined as each species entered the community progressively later than its competitor and as aggression by its competitor increased. Intraspecific effects of resident T. hardwicke were similar to interspecific effects. This study shows that the strength of competition depends not only on the identity of competitors, but also on the sequence and timing of their interactions, suggesting that when examining interaction strengths, it is important to identify temporal variability in the direction and magnitude of their effects. Furthermore, our findings provide empirical evidence for the importance of competitive lotteries in the maintenance of species diversity in demographically open marine systems.

The behavior of marine larvae during and after settlement can help shape the distribution and abundance of benthic juveniles and therefore the intensity of ecological interactions on reefs. Several laboratory choice-chamber experiments were conducted to explore sensory capabilities and behavioral responses to ecological stimuli to better understand habitat selection by “pre-metamorphic” (larval) and “post-metamorphic” (juvenile) stages of a coral reef fish (Thalassoma hardwicke). T. hardwicke larvae were attracted to benthic macroalgae (Turbinaria ornata and Sargassum mangarevasae), while slightly older post-metamorphosed juveniles chose to occupy live coral colonies (Pocillopora damicornis). Habitat choices of larvae were primarily based upon visual cues and were not influenced by the presence of older conspecifics. In contrast, juveniles selected live coral colonies and preferred those occupied by older conspecifics; choices made by juveniles were based upon both visual and olfactory cues from conspecifics. Overall, the laboratory experiments suggest that early life-history stages of T. hardwicke use a range of sensory modalities that vary through ontogeny, to effectively detect and possibly discriminate among different microhabitats for settlement and later occupation. Habitat selection, based upon cues provided by environmental features and/or by conspecifics, might have important consequences for subsequent competitive interactions.

Density-dependent mortality can regulate local populations - effectively minimizing the likelihood of lo- cal extinctions and unchecked population growth. It is considered particularly important for many marine reef organisms with demographically open populations that lack potential regulatory mechanisms tied to local repro- duction. While density-dependent mortality has been doc- umented frequently for reef fishes, few studies have ex- plored how the strength of density-dependence varies with density, or how density-dependence may be modi- fied by numerical effects (i.e., number-dependent mortali- ty). Both issues can have profound effects on spatial pat- terns of abundance and the regulation of local popula- tions. I address these issues through empirical studies in Moorea, French Polynesia, of the six bar wrasse ( Thalas- soma hardwicke), a reef fish that settles to isolated patch reefs. Per capita mortality rates of newly settled wrasse increased as a function of density and were well approxi- mated by the Beverton-Holt function for both naturally formed and experimentally generated juvenile cohorts. Average instantaneous mortality rates were a decelerating function of initial densities, indicating the per capita strength of density-dependence decreased with density. Results of a factorial manipulation of density and group size indicate that per capita mortality rates were simulta- neously density- and number-dependent; fish at higher densities and/or in groups had higher probabilities of dis- appearing from patch reefs compared with fish that were solitary and/or at lower densities. Mortality rates were ~30% higher for fish at densities of 0.5 fish/m 2 than at 0.25 fish/m 2 . Similarly, mortality rates increased by ~45% when group size was increased from 1 to 2 individ- uals per patch, even when density was kept constant. These observations suggest that the number of interact- ing individuals, independent of patch size (i.e., density- independent effects) can contribute to regulation of local populations. Overall, this work highlights a greater need to consider numerical effects in addition to density effects when exploring sources of population regulation.