The influence of biotic interactions on settlement and post-settlement processes in corals, and the role of early life history dynamics in driving coral community structure and diversity maintenance

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

10.26686/wgtn.14176475 ◽

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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Early Life-History Dynamics of Caribbean Octocorals: The Critical Role of Larval Supply and Partial Mortality

Frontiers in Marine Science ◽

10.3389/fmars.2021.705563 ◽

2021 ◽

Vol 8 ◽

Author(s):

Ángela Martínez-Quintana ◽

Howard R. Lasker

Keyword(s):

Life History ◽

Early Life ◽

Critical Role ◽

Early Life History ◽

Larval Supply ◽

Partial Mortality ◽

Potential Growth ◽

Survival And Growth ◽

The Caribbean

Recruitment is a key demographic process for maintenance of local populations and recovery following disturbance. For marine invertebrates, distribution and abundances of recruits are impacted by spatiotemporal variation in larval supply, settlement rates and post-settlement survival. However, for colonial and modular organisms, differences in survival and growth between settlers and colonial recruits may also affect recruitment patterns. In the Caribbean, shifts in the benthic community structure favoring octocoral’s have been detected, and recruitment has been suggested as key for octocoral’s resilience. Hence, we studied octocoral recruitment dynamics, and evaluated the role of pre-settlement, settlement and post-settlement processes in recruit’s densities. We performed the study at two sites with different octocoral densities, on the south coast of St. John, United States Virgin Islands, and distinguished between processes occurring to recently settled polyps and to colonial recruits. At both sites, we monitored P. homomalla settlers on settlement tiles for 3 months, and colonial recruits of two of the most abundant genera (Eunicea and Pseudoplexaura) for 3 years. In addition, we assessed whether recruits morphological traits affected recruitment and divided recruits of the genus Eunicea based on the presence of large calyces. The major contributor to both, single-polyps and colonial recruit densities was larval supply. Single-polyp densities were not limited by the availability of space, settlement cues, or early post-settlement survival. Height was the only predictor of survival and growth of colonial recruits, with potential growth rates increasing with height. However, large recruits suffered partial mortality often, distorting the relationship between recruit age and size, and causing most recruits to remain in the recruit size class (≤5 cm) longer than a year. Octocorals have been resilient to the conditions that have driven the decline of scleractinian corals throughout the Caribbean, and recruitment has been key to that success. Our results are crucial to understand early life history dynamics of Caribbean octocorals, and highlights the need to standardize the definition of recruit among colonial and modular taxa to facilitate inter-specific comparisons, and to understand future changes in coral reef community assemblages.

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