Environmental variability, early life-history traits, and survival of new coral reef fish recruits

<p>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). </p><p><br></p> 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.<div><br>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.</div><div><br></div><div>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.</div>

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Selective mortality on early life-history traits of a temperate reef fish

10.26686/wgtn.17014277.v1 ◽

2021 ◽

Author(s):

◽

Phoebe Caie

Keyword(s):

Life History ◽

Developmental Stage ◽

Reef Fish ◽

Early Life ◽

Life History Traits ◽

Larval Growth ◽

Early Life History ◽

Selective Mortality ◽

Density Dependent ◽

Larvae And Juveniles

<p>Variability in recruitment and early life-history traits is widespread in many marine organisms. Phenotypic variation is particularly prevalent in the early life-history stages (e.g., larvae and juveniles) of reef fish, and provides the basis for selective mortality on growth and size-related traits, with important ecological and evolutionary consequences. Recruitment variability can alter the effective densities experienced by these early life stages, raising additional questions about the interplay between selection and density-dependent processes. While many examples of growth- and size-selective mortality have been documented for young reef fish (typically caused by predators), few studies consider how the strength and/or direction of selective mortality changes with ontogeny, or how these patterns may be mediated by density. I explore spatio-temporal variability in early life-history traits of the common triplefin, Forsterygion lapillum, using metrics derived from otoliths (a re-analysis of two previously collected data sets). I evaluate patterns of variation in traits with respect to early life-history stage (either larvae or post-settlement juveniles) and document shifts in the distributions of traits that are consistent with selective mortality favouring slower growing individuals. I conclude that a cohort of juveniles (sampled after settlement) was comprised of individuals that were smaller at hatch and grew slowly throughout the pelagic larval period relative to a cohort of larvae (sampled prior to settlement). I then conducted an experiment using a set of mesocosms to evaluate whether selective mortality on early life-history traits in common triplefin could be caused by a natural predator, the variable triplefin, Forsterygion varium. Specifically, I exposed groups of fish of each stage to a pair of predators and I used otoliths to reconstruct the traits of fish that survived versus fish that were consumed (i.e., I recovered otoliths from the guts of predators). Selection trials were conducted across realistic density gradients for each developmental stage. Fish size was negatively correlated with relative fitness for larvae (indicating larger fish were consumed preferentially by predators) but not for juveniles (where no size-selective mortality was observed). These patterns were consistent across the range of densities evaluated. Both larvae and juveniles experienced significant selection against fast larval growth (estimated from growth increments in otoliths), and the strength of selection was inversely related to density (i.e., strongest at lower densities, weakest at higher densities). However, juveniles also experienced selective predation for fast growth at the larval-juvenile transition. As with larval growth, selection was strongest at lower densities and weakest at higher densities. Collectively, these results suggest that predators may preferentially target larger larvae, and faster growing individuals regardless of developmental stage. However, this effect may be mediated by density, such that the strongest selection occurs during low recruitment. Density-dependent selection could explain how faster growing individuals can survive this vulnerable stage. These results provide evidence for carry-over effects of larval growth on juvenile survival, and suggest conspecific density should be considered when evaluating patterns of selective mortality.</p>

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Selective mortality on early life-history traits of a temperate reef fish

10.26686/wgtn.17014277 ◽

2021 ◽

Author(s):

◽

Phoebe Caie

Keyword(s):

Life History ◽

Developmental Stage ◽

Reef Fish ◽

Early Life ◽

Life History Traits ◽

Larval Growth ◽

Early Life History ◽

Selective Mortality ◽

Density Dependent ◽

Larvae And Juveniles

<p>Variability in recruitment and early life-history traits is widespread in many marine organisms. Phenotypic variation is particularly prevalent in the early life-history stages (e.g., larvae and juveniles) of reef fish, and provides the basis for selective mortality on growth and size-related traits, with important ecological and evolutionary consequences. Recruitment variability can alter the effective densities experienced by these early life stages, raising additional questions about the interplay between selection and density-dependent processes. While many examples of growth- and size-selective mortality have been documented for young reef fish (typically caused by predators), few studies consider how the strength and/or direction of selective mortality changes with ontogeny, or how these patterns may be mediated by density. I explore spatio-temporal variability in early life-history traits of the common triplefin, Forsterygion lapillum, using metrics derived from otoliths (a re-analysis of two previously collected data sets). I evaluate patterns of variation in traits with respect to early life-history stage (either larvae or post-settlement juveniles) and document shifts in the distributions of traits that are consistent with selective mortality favouring slower growing individuals. I conclude that a cohort of juveniles (sampled after settlement) was comprised of individuals that were smaller at hatch and grew slowly throughout the pelagic larval period relative to a cohort of larvae (sampled prior to settlement). I then conducted an experiment using a set of mesocosms to evaluate whether selective mortality on early life-history traits in common triplefin could be caused by a natural predator, the variable triplefin, Forsterygion varium. Specifically, I exposed groups of fish of each stage to a pair of predators and I used otoliths to reconstruct the traits of fish that survived versus fish that were consumed (i.e., I recovered otoliths from the guts of predators). Selection trials were conducted across realistic density gradients for each developmental stage. Fish size was negatively correlated with relative fitness for larvae (indicating larger fish were consumed preferentially by predators) but not for juveniles (where no size-selective mortality was observed). These patterns were consistent across the range of densities evaluated. Both larvae and juveniles experienced significant selection against fast larval growth (estimated from growth increments in otoliths), and the strength of selection was inversely related to density (i.e., strongest at lower densities, weakest at higher densities). However, juveniles also experienced selective predation for fast growth at the larval-juvenile transition. As with larval growth, selection was strongest at lower densities and weakest at higher densities. Collectively, these results suggest that predators may preferentially target larger larvae, and faster growing individuals regardless of developmental stage. However, this effect may be mediated by density, such that the strongest selection occurs during low recruitment. Density-dependent selection could explain how faster growing individuals can survive this vulnerable stage. These results provide evidence for carry-over effects of larval growth on juvenile survival, and suggest conspecific density should be considered when evaluating patterns of selective mortality.</p>

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Early life history variation in phenotypes and fitness of a coral reef fish, Thalassoma hardwicke

10.26686/wgtn.14176475.v1 ◽

2021 ◽

Author(s):

Phoebe Caie

Keyword(s):

Life History ◽

Coral Reef ◽

Spatial Variation ◽

Reef Fish ◽

Early Life ◽

Early Life History ◽

Agonistic Interactions ◽

Growth History ◽

Environment Gradients

<p>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). </p><p><br></p> 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.<div><br>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.</div><div><br></div><div>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.</div>

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Coral reef fish community life history traits as potential global indicators of ecological and fisheries status

Ecological Indicators ◽

10.1016/j.ecolind.2018.08.055 ◽

2019 ◽

Vol 96 ◽

pp. 133-145 ◽

Cited By ~ 3

Author(s):

T.R. McClanahan

Keyword(s):

Life History ◽

Coral Reef ◽

Reef Fish ◽

Coral Reef Fish ◽

Fish Community ◽

Life History Traits ◽

Community Life ◽

Reef Fish Community ◽

Global Indicators

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