One common consequence of ontogenetic niche shifts is that juveniles and adults of the same species often use different resources and habitats. Theory suggests that variation in productivity and/or habitat size for the respective life stage regulates size distribution of individuals and population biomass. Low resources/habitat availability for juveniles relative to adults results in populations with many small juveniles with high mortality and few but large adults, while the opposite situation results in a population with small and slow growing adults with high densities. I tested this theory using lake-living brown trout (Salmo trutta), where adults inhabit lakes and use connected streams for spawning and nurseries for juveniles. My hypothesis was that the relative habitat availability for juveniles respectively adults determines the size structure of adult brown trout in lakes. This was done by quantifying available stream habitats in relation to lake area via GIS analysis of 101 allopatric brown trout lakes in Sweden and Norway. My results showed that the proportion of large trout, mean length and maximum length decreased with increasing juvenile habitat in relation to adult habitat availability. This suggests that relative variation in availability of juvenile and adult habitats can affect the size structure of lake-living brown trout, most likely due to size dependent niche shifts and competitive and cannibalistic interactions. As the lake brown trout is highly valued both for commercial and recreational purposes, these findings can be highly valuable for sustainable management of the ecosystems services that the brown trout provides.

Testing ecological theory at macroecological scales may be useful for disentangling abiotic influences from anthropogenic disturbances, and thus provide insights into fundamental processes that structure ecological communities. In tropical coral reef systems, our understanding of community structure is limited to small-scale studies conducted in moderately degraded regions, while larger regional or ocean scale analyses have typically focused on identifying human drivers of reef degradation. In this thesis, my collaborators and I combined stable isotope specimens, underwater visual censuses, and remote sensing data from 43 Pacific islands and atolls in order to examine the relative roles of natural environmental variation and anthropogenic pressures in structuring coral reef fish and benthic communities. First, at unexploited sites on Kiritimati Atoll (Kiribati), isotope estimates indicated that trophic level increased with body size across species and individuals, while negative abundance ~ body size relationships (size spectra) revealed distinct energetic constraints between energy-competing carnivores and energy-sharing herbivores. After demonstrating size structuring of reef fish communities in the absence of humans, we then examined evidence for size-selective exploitation impacts on coral reefs across the Pacific Ocean. Size spectra 'steepened' as human population density increased and proximity to market center decreased, reflecting decreases in large-bodied fish abundance, biomass, turnover rate, and mean trophic level. Depletion of large fish abundances likely diminishes functions such as bioerosion by grazers and food chain connectivity by top predators, further degrading reef community resilience. Next, we considered the relative strengths of abiotic, biotic and anthropogenic influences in determining reef benthic state across spatial scales. We found that from fine (0.25 km2) to coarse (1,024 km2) grain scales the phase shift index (a multivariate metric of the relative cover of hard coral and macroalgal) was primarily predicted by local abiotic and bottom-up influences, such that coral-dominated reefs occurred in warm, productive regions at sites exposed to low wave energy, irrespective of grazing or human impacts. Our size- based analyses of reef fish communities revealed novel exploitation impacts at ocean-basin scales, and provide a foundation for delineating energetic pathways and feeding interactions in complex tropical food webs. Furthermore, we demonstrate that abiotic constraints underpin natural variation among fish and benthic communities of remote uninhabited reefs, emphasizing the importance of accounting for local environmental conditions when developing quantitative baselines for coral reef ecosystems. / Graduate / 0329

Body size is important in determining the outcome of competition and predator-prey interactions. Size structure of a population (i.e. relative proportion of large and small conspecifics) may be particularly important in organisms with prolonged breeding periods and rapid growth where populations may have multiple cohorts at different stages of development competing for one resource. Both the consumptive and nonconsumptive effects of predators can also be size-dependent and can alter competitive interactions. Here we study the importance of size structure in the Neotropical leaf-breeding tree frog, Agalychnis callidryas. This species is a prolonged breeder such that multiple overlapping cohorts of differing sizes are common. Specifically, we examine size-specific intraspecific competition between A. callidryas tadpoles and then explore how predation affects these interactions. To determine the strength of inter-cohort competition, we manipulated the density and relative proportion of large and hatchling tadpoles in a response surface design and quantified growth. We then observed the effect of a dragonfly larvae predator (Anax amazili) on tadpole growth and survival at different size-structured treatments. Large tadpoles were greater per individual competitors while hatchlings were greater per gram competitors. When predators were added, dragonflies reduced survival and growth of hatchlings substantially, but had no effect on large tadpoles. Further, dragonflies reduced hatchling growth more when other hatchlings were present. The predator effect on hatchling growth was 23% larger than the effect of competition with large tadpoles, such that the importance of size structure for A. callidryas may be mediated more through predation than intercohort competition.

In this study, the factors influencing zooplankton community structure in Turkish shallow lakes were elucidated with four main approaches: (i) space-for-time substitution for shallow lakes using snap-shot sampling in 31 lakes along a latitudinal gradient / (ii) in-situ mesocosm experiments in eleven lakes along a latitudinal gradient using three sets of artificial plants systems / (iii)&lsquo / Habitat Choice&rsquo / laboratory experiments mimicking a &lsquo / shallow littoral&rsquo / zone with plants and a &lsquo / deeper pelagic&rsquo / zone with sediments testing the response of Daphnia magna to predation cues / and (iv) long-term monitoring data (1997-2011) from two interconnected lakes. Snap-shot and long-term monitoring showed that eutrophication has a strong influence on the zooplankton community via increased fish predation, nutrient loading and salinization. Here too the zooplankton community shifted towards a smaller sized profile, especially in lakes located at lower latitudes. Moreover, The laboratory and in-situ mesocosm experiments revealed that under predation risk Daphnia preferred to hide near sediment instead of using submerged plants as a refuge. Accordingly, in-situ mesocosm experiments revealed a predation pressure induced size structure shift towards small-medium sized zooplankton and calanoid copepods. The long-term monitored lakes experienced (i) drought-induced water level drop, leading to increased salinity and eutrophication, and consequent anoxic conditions and fish kill / as well as (ii) biomanipulation in the downstream. Both conditions resulted in major reduction in the top-down control of fish and ultimate predomination by large sized Daphnia spp. Nevertheless, the excessive exploitation of lakes and ongoing warming entail Turkish shallow lakes to become more eutrophic, making this study indicative for the Mediterranean region.

[Truncated abstract] Most ecological research investigates the demography of organisms, which can be summarised by their population dynamics and structure. Population dynamics are the rates of birth, growth, reproduction and survival of individuals, which determine the number of individuals in different stage classes, or, the population structure. Understanding the demography of organisms is particularly difficult, and requires the application of different methods of investigation. A number of methods of investigation are required because each can only investigate particular aspects of population demography, and is subject to problems of inaccuracy and bias. Thus, population demography is best understood by simultaneously collecting complimentary data using different methods of analysis to quantify how and why the dynamics and structure of populations change with their environment. The need for complimentary methods of investigation to understand population demography is even greater for organisms that have complex life histories, such as corals. The life histories of corals are particularly complex because they display a variety of modes of sexual and asexual reproduction, and their rates of growth, reproduction and survival are strongly influenced by the size of the individual, which can change rapidly. Additionally, the rates of sexual recruitment to populations of corals are notoriously variable in space and time. Thus, corals are an ideal model to investigate the usefulness of combining methods of analysis to better understand the demography of organisms. In this thesis I demonstrate that combining data from a number of methods of analysis provides a much better understanding of the demography of populations of the mushroom coral Fungia fungites that were exposed to contrasting regimes of disturbance. I used methods of analysis that produce unique and complimentary results, in the form of genetic, size-structure, life history and experimental data. Genetic data confirmed that I was correctly identifying life history stages of polyps, indicated the extent to which a stock-recruitment relationship existed between the sexual recruits and the adult polyps at each population, and provided an estimate of the relative contribution of asexual recruitment to population maintenance. Changes in the size-structures of populations were quantified to determine the effects of different regimes of disturbance, and these changes in population structure were explained by quantifying the life history traits of polyps and their rates of transition through their life cycle. An experimental manipulation was conducted to specifically quantify the effects of sedimentation on the rates of survival and asexual recruitment of polyps, because sedimentation was an important disturbance whose effects were confounded by additional variables. Together, the set of complimentary data provided a good understanding of population demography in the context of varying levels of exposure to certain disturbances, and enabled the best possible predictions about the future of each population under a variety of conditions

Understanding how temperature affects biological systems is a central question in ecology and evolutionary biology. Anthropogenic climate change adds urgency to this topic, as the demise or success of species under climate change is expected to depend on how temperature affects important aspects of organismal performance, such as growth, development, survival and reproduction. Rates of biological processes generally increase with increasing temperature up to some maximal temperature. Variation in the slope of the initial, rising phase has attracted considerable interest and forms the focus of this thesis. I explore variation in growth rate-temperature relationships over several levels of biological organization, both between and within species, over individuals’ lifetime, depending on the ecological context and in relation to important life history characteristics such as generation length and winter dormancy.       Specifically, I examine how a clade of temperate damselflies have adapted to their thermal environment along a 3,600 km long latitudinal transect spanning from Southern Spain to Northern Sweden. For each of six species, I sampled populations from close to the northern and southern range margin, as well from the center of the latitudinal range. I reared larvae in the laboratory at several temperatures in order to measure indiviudal growth rates. Very few studies of thermal adaptation have employed such an extensive sampling approach, and my finding reveal variation in temperature responses at several levels of organization.       My main finding was that temperature responses became steeper with increasing latitude, both between species but also between latitudinal populations of the same species. Additional genetic studies revealed that this trend was maintained despite strong gene flow. I highlight the need to use more refined characterizations of latitudinal temperature clines in order to explain these findings. I also show that species differ in their ability to acclimate to novel conditions during ontogeny, and propose that this may reflect a cost-benefit trade-off driven by whether seasonal transitions occur rapidly or gradually during ontogeny.       I also carried out a microcosm experiment, where two of the six species were reared either separately or together, to determine the interacting effects of temperature and competition on larval growth rates and population size structure. The results revealed that the effects of competition can be strong enough to completely overcome the rate-depressing effects of low temperatures. I also found that competition had stronger effects on the amount of variation in growth rates than on the average value.       In summary, my thesis offers several novel insights into how temperature affects biological systems, from individuals to populations and across species’ ranges. I also show how it is possible to refine our hypotheses about thermal adaptation by considering the interacting effects of ecology, life history and environmental variation.

Climate change and introduced species are among the top five threats to freshwater systems face. Tropical regions are considered to be especially sensitive to the effects of climate change, while island systems are more susceptible to species introductions. Climate-driven changes in rainfall are predicted to decrease streamflow and increase flash flooding in many tropical streams. In addition, guppies (Poecilia reticulata), an invasive fish, have been introduced to many tropical freshwater ecosystems, either intentionally for mosquito population control, or accidentally because of the aquarium trade. This dissertation examines the effects of climate-driven change in rainfall and introduced guppies on stream structure (resource and invertebrate biomass and composition) and function (nutrient recycling) in Trinidad and Hawaii. In the first data chapter we used a time series to examine how nutrient recycling of guppies changes in the first 6 years after introduction to a new habitat and to examine drivers of these changes. We found that when guppy populations establish in a new environment, they show considerable variation in nutrient recycling through time. This resulted from changes in guppy density in the first two years of introductions, and changes in individual excretion in subsequent stages. In the following chapter we utilized a rainfall gradient that mimics forecasted, climate-driven changes in precipitation and resulting changes in streamflow to examine the effects of climate change on stream food resources and macroinvertebrates. We found that the drying of streams across the gradient was associated with a decrease in resource quality and a 35-fold decline in macroinvertebrate biomass. Invertebrate composition also switched to taxa with faster turnover rates. In the third data chapter we used this same space-for-time substitution approach to determine if climate-driven changes in stream structure also affected stream function. We showed that population nutrient recycling rates declined at the drier end of our rainfall gradient as a result of drops in population densities. We also found that under the current climate scenario, community excretion supplied up to 70% of the nutrient demand, which was ten-fold lower with projected climate changes in streamflow. Lastly, since freshwater ecosystems often face multiple human impacts, including climate change and invasive species, we wanted to understand how climate-driven changes in flow might alter the impact of introduced guppies on stream ecosystems. We selected several streams with guppies and several without guppies along the Hawaii rainfall gradient to examine if the effect of guppies changed with differences in streamflow. We found that the two stressors had synergistic effects on macroinvertebrate biomass and nutrient recycling rates. We concluded that climate change appeared to enhance effects of guppies, through direct and indirect effects. Overall, this dissertation shows that both climate change and species invasion can affect stream ecosystems at multiple levels of organization. This dissertation demonstrates that the effects of anthropogenic stressors are not static through time, and emphasizes the need and utility of using several methodological approaches when measuring the temporal effects of stressors. We also underline the significance of assessing multiple stressor interactions, as more than one stressor often impacts ecosystems. / Graduate / 2019-09-01

Made available in DSpace on 2015-03-05T16:19:36Z (GMT). No. of bitstreams: 0 Previous issue date: 26 / Nenhuma / Este estudo foi realizado em dez fragmentos de floresta ripária localizados no sul do Brasil (30°09’S, 51°36’W; 46 m de altitude). Entre as dez florestas ripárias selecionadas, cinco estavam circundadas por pastejo de gado e as outras cinco estavam circundadas por plantações de eucalipto. Foi avaliada a sustentabilidade de Campomanesia rhombea, Diospyros inconstans, Myrciaria cuspidata e Sebastiania commersoniana através de análises da estrutura de tamanho, as quais foram realizadas em duas escalas. Em escala local, foram consideradas as populações presentes nos fragmentos circundados por pastejo de gado ou por plantações de eucalipto e, em escala regional considerou-se também áreas florestais maiores, tomadas como referência (Inventário Florestal Contínuo do Rio Grande do Sul). Em escala local, nas populações presentes em fragmentos circundados por plantações de eucalipto, prevaleceram indivíduos de pequenas classes de tamanho, e em áreas expostas ao pastejo de gado, as mesmas espécies apresentaram uma falha / This studied was carried in ten riparian forest fragments located southern Brazil. Of the ten riparian forests selected for study, five were embedded in pasturelands and five in eucalyptus plantations. We assessed the population sustentability of Campomanesia rhombea, Diospyros incontans, Myrciaria cuspidata and Sebastiania commersoniana through analyses of size structure, which were carried out at two scales. At a local scale, we consider populations in fragments surrounded by pastures or eucalyptus forest plantations, and at a regional scale we also consider larger forest tracts taken as reference areas (Rio Grande do Sul Forest Inventory databank). At local scale, the populations in fragments embedded by eucalyptus plantations prevailed small size classes individuals, and in areas exposed to cattle ranching, the same species seem to have a recurring failure of small individuals. Regional analyses included only established individuals with DBH > 1.6 cm. In this scale, populations in fragments surrounded by

The main goal of this study was to evaluate the effectiveness of two biological control agents in reducing population growth and spread of the invasive tree Melaleuca quinquenervia, a subtropical tree native to Australia, and invasive in Florida, Puerto Rico, and the Bahamas. While in Florida two insects Oxyops vitiosa (weevil), and Boreioglycaspis melaleucae (psyllid) have been established as biocontrol agents, in Puerto Rico only psyllids are present, and in the Bahamas no biocontrol agents are present. This study combined demographic data, experiments and mathematical models to investigate the influence of the biocontrol agents on M. quinquenervia's spatial population dynamics. In the field, permanent plots were established and demographic data was collected in populations in the native and exotic ranges. Australian populations are comprised mostly of tall adult trees, while in the exotic ranges populations are comprised mostly of short trees (<1.3m in height), and small adult trees. In a shade-house, I performed an experiment to investigate the effects of insect type and density on survival and growth of M. quinquenervia seedlings. I found that high density of insects, independently or in combination, reduce seedling performance, thus having the potential to alter the seedling-short plant transition of the M. quinquenervia life cycle. Based on the demographic data, I developed integral projection models (IPMs) to determine population growth rates in each region. Populations in Australia and the Bahamas are increasing, while populations in Florida and Puerto Rico are decreasing. Population growth is most sensitive to the seedling-short plant transition in all regions, except Florida, where it is most sensitive to survival of tall plants. Simulations combining the results of the IMPs and experiment indicated the biocontrol damage results in reductions in population growth rate in Puerto Rico and the Bahamas. Seed dispersal and demographic data was combined to develop an integrodifference structured model of population spread. Simulations indicated that by reducing seedling performance, insects have the potential to reduce the rate of population spread. Overall this study shows that individual-level effects of biocontrol agents have translated into reductions in population growth rate and rate of spread of M. quinquenervia.

Submitted by Caroline Falcao (caroline.rfalcao@ufpe.br) on 2017-05-22T17:32:45Z No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese__Aschenbrenner_versão_Definitiva.pdf: 1827049 bytes, checksum: 2b2e0b82d6dc856801226f7368d28b5b (MD5) / Made available in DSpace on 2017-05-22T17:32:45Z (GMT). No. of bitstreams: 2 license_rdf: 1232 bytes, checksum: 66e71c371cc565284e70f40736c94386 (MD5) Tese__Aschenbrenner_versão_Definitiva.pdf: 1827049 bytes, checksum: 2b2e0b82d6dc856801226f7368d28b5b (MD5) Previous issue date: 2014-11-25 / O objetivo geral desta tese foi avaliar a conectividade entre ecossistemas costeiros e plataforma continental para a espécie L. alexandrei e estudar a utilização destas áreas em diferentes estágios do ciclo de vida para L. alexandrei e L. jocu na região costeira de PE. Para entender melhor a movimentação entre estas áreas, foram utilizados diferentes métodos combinados: (1) a estrutura etária e de tamanho de L. alexandrei foi determinada para áreas estuarinas (profundidades < 5m) e costeiras (profundidades entre 30 a 60 m) metros da plataforma continental; (2) a assinatura química de otólitos de indivíduos de L. alexandrei capturados em áreas estuarinas e costeiras foi analisada para evidenciar a variação ontogenética na permanência entre os diferentes habitats; (3) a presença em áreas estuarinas e recifes rasos adjacentes a costa em diferentes estágios do ciclo de vida foi detectada e quantificada para L. alexandrei e L. jocu através de censos visuais subaquáticos. Amostras biológicas (otólitos) de L. alexandrei foram coletadas através do acompanhamento de desembarques da pesca de Camboa em regiões estuarinas e pesca de rede e armadilhas em regiões costeiras entre o litoral dos estados de Pernambuco e Alagoas. As coletas foram realizadas durante três anos consecutivos (2010-2012). Otólitos de indivíduos juvenis e adultos foram extraídos, emblocados em resina, seccionados utilizando uma serra metalográfica e analisados inicialmente quanto à sua estrutura etária. Em uma segunda etapa, secções de otólitos foram analisadas com relação à sua assinatura química através de um espectrômetro de massa com ablação a laser. Observações subaquáticas foram realizadas em mangues (duas localidades) e recifes de coral adjacentes (três localidades) (a partir de 90 transectos de 10 x 2 m para cada localidade) durante os meses de novembro a março (2012- 13). Resultados da analise de distribuição etaria mostram que para áreas estuarinas indivíduos apresentaram idades de 0 a 4 anos, enquanto indivíduos coletados em áreas costeiras mais profundas foram mais velhos,entre 3 a 22 anos, indicando que uma mudança entre habitats ocorre aproximadamente entre idades 3 e 4. A frequência do tipo de borda ao longo de um ano utilizado para validar a deposição anual de anéis etários indica que, a formação da banda opaca ocorre no período chuvoso, entre abril e setembro. Dados de crescimento revelam que L. alexandrei possui um crescimento rápido durante os estágios iniciais de vida, atingindo em média 50% de seu tamanho assintótico com idade 2. Parâmetros da curva do modelo de crescimento de von Berlalanffy encontrados para L. alexandrei foram L∞ = 31 cm , k = 0.24, t0 = -1.26, r2 = 0.97. A taxa de mortalidade estimada para indivíduos coletados em áreas costeiras foi Z = 0.22 com sobrevivência de S = 0.78 year-1 . Para a analise microquímica dos otólitos foram medidos seis elementos: 7 Li, 24Mg, 55Mn, 59Co, 88Sr and 137Ba para indivíduos de L. Alexandrei. A analise de material recentemente depositado na borda de otólitos revelou que concentrações na razão elemento:Ca não variaram significativamente ao longo dos três anos testados. Similarmente, com exceção de dois elementos (Ba, Co), a razão elemento:Ca para indivíduos maiores habitando águas costeiras também foi estável, não apresentando diferenças para as diferentes regiões costeiras investigadas. Contrariamente, assinaturas químicas em otólitos de L. alexandrei de tamanhos similares provenientes da região estuarina e áreas costeiras foram distintas. Concentrações de Mn:Ca e Ba:Ca em otólitos foram ambos significativamente maiores para L. alexandrei coletados na região estuarina comparados a peixes coletados na região costeira adjacente, enquanto que para Sr:Ca uma tendência oposta foi observada. Dadas as diferenças pronunciadas na assinatura química entre áreas estuarina e costeiras, transectos de elemento:Ca foram construídos desde a região do núcleo até a margem em otólitos de indivíduos coletados em áreas costeiras para determinar o tempo de movimento (migração ontogenética) entre estuário e áreas costeiras. Concentrações de Mn:Ca e Ba:Ca mostraram um padrão semelhante ao esperado, com maiores concentrações para idades 1 e 2, com diminuição gradual para idades subsequentes. Este padrão sugere que espécimes de L. alexandrei começam a transição para habitats mais costeiros (e.g. menores concentrações de Mn e Ba) após a idade 2. Dados de observações subaquáticas corroboraram estes resultados, revelando que para ambas as espécies, indivíduos menores que 10 cm ocorrem exclusivamente em manguezais. Uma nítida mudança foi observada com um aumento de densidades para indivíduos acima de 10 cm em áreas recifais adjacentes. Para L. alexandrei a ocorrência de pos-assentantes, juvenis e subadultos foi registrada em manguezais enquanto que em recifes adjacentes apenas subadultos e adultos foram registrados. Padrão semelhante foi observado para L. jocu com individuos pos-assentantes, juvenis e subadultos em manguezais e juvenis e subadultos habitando recifes rasos adjacentes. Informações obtidas nesta Tese permitiram uma melhor compreensão dos padrões de crescimento e estrutura etária de L. alexandrei. Resultados sugerem ainda a movimentação ontogenética de L. alexandrei entre habitas costeiros e regiões costeiras mais profundas e permitem uma melhor compreensão da utilização de habitats costeiros em estágios iniciais de vida para as espécies de L. alexandrei e L. jocu. / Current objective of this thesis was to evaluate the connectivity among a shallow nursery area and deeper coastal ecossystems for L. alexandrei, and study utilization of such habitats in different life stages for L. alexandrei and L. jocu in the coastal areas of Pernambuco. In order to better understand movement between these areas, combined methods were applied: (1) initially age structure and size of L. alexandrei individuals were determined between estuarine (depths < 5 m) and deeper coastal areas (depths between 30 and 60 m); (2) otoliths microquimistry of L. alexandrei caught in estuarine and coastal areas were tested to evidence possible movement between these areas; (3) the utilization of mangroves and adjacent shallow reef areas in different life stages were studied through underwater visual census for L. alexandrei and L. jocu. Biological samples (otoliths) of L. alexandrei were collected through fishing landings of corral fisheries in estuarine areas and guillnets and traps for coastal areas between Pernambuco and Alagoas States. Data were collected during three consecutive years (2010- 2012). Otoliths of both juvenile and adult individuals were extracted, embedded in resin, sectioned with a low speed saw, then age structure were determined. In a second step, chemical concentrations of trace elements were analyzed in otolith sections using a laser ablation inductively coupled plasma mass spectrometer. Underwater observations (Total 90 transects of 10 x 2 m for each of the five locations) were performed along November to March (2012-13). Results show that inshore mangroves were comprised of individuals 0 to 4 years (mean: 2) while individuals in deeper reef environments were older (range: 3 to 22; mean: 8), indicating that an ontogenetic shift occurs at approximately age 3 or 4. Edge analysis was used to validate the annual deposition in the otoliths suggesting opaque growth rings were formed in the wet season between April and September. Growth data revealed that L. alexandrei display a faster growth in early life stages, reaching approximately 50% of its asymptotic size at age 2. Age at length data were used to predict growth rates of L. alexandrei using the von Bertalanffy growth model from where the following parameters were calculated: L∞ = 31 cm , k = 0.24, t0 = -1.26, r2 = 0.97. Mortality rates were estimated for coastal habitats, with Z = 0.22 and S = 0.78 year-1 . Concentrations of six trace elements were measure (7 Li, 24Mg, 55Mn, 59Co, 88Sr and 137Ba) in otoliths of L. alexadrei. Element:Ca ratios in the otoliths of juvenile and sub-adult L. alexadrei from estuaries were not significantly different among three consecutive years (2010, 2011 and 2012), suggesting that physicochemical conditions within the nursery investigated was temporally stable. Similarly, apart from two element (Ba, Co), element:Ca ratios for larger L. alexandrei inhabiting coastal waters were also similar. In contrast, otolith chemistry of similar sized L. alexandrei from estuarine and coastal areas was distinctly different (based on recently accreted material). Otolith Mn:Ca and Ba:Ca were both significantly higher for L. alexandrei collected in estuaries compared to fish from adjacent coastal reefs region, while the opposite trend was observed for Sr:Ca. Given the pronounced differences in otolith chemistry between estuarine and coastal areas, element:Ca transects were constructed from the core to margin of the otoliths for adults (age 7+) collected on reefs to determine the timing of movement (ontogenetic migration) from estuarine to coastal areas. Based on observed patterns of decline for both Mn:Ca and Ba:Ca, it appears that L. alexandrei begin to transition to more coastal habitats (i.e., lower element:Ca ratios) after age 2. Underwater observations indicate that for both species, individuals smaller than 10 cm occurred exclusively in mangroves. A distinct shift was observed with higher densities for individuals larger than 10 cm in adjacent shallow reef areas. For L. alexandrei mangroves registered occurrence of (postsettlers, juveniles and subadults) while for shallow reefs only (subadults and adults) were observed. A similar pattern was observed for L. jocu with individuals (postsettlers, juveniles and subadults) in mangroves and (juveniles and subadults) inhabiting shallow reefs. General information provided in this thesis allow a better understanding of size structure and growth pattern for L. alexandrei. Yet results suggest ontogenetic migration for L. alexandrei between shallow coastal and deeper marine habitats as well as a better understanding of habitat utilization in early life stages for L. alexandrei and L. jocu.