Fast Algorithms for Geometric Consensuses

Let P be a set of n points in ?^d in general position. A median hyperplane (roughly) splits the point set P in half. The yolk of P is the ball of smallest radius intersecting all median hyperplanes of P. The egg of P is the ball of smallest radius intersecting all hyperplanes which contain exactly d points of P. We present exact algorithms for computing the yolk and the egg of a point set, both running in expected time O(n^(d-1) log n). The running time of the new algorithm is a polynomial time improvement over existing algorithms. We also present algorithms for several related problems, such as computing the Tukey and center balls of a point set, among others

Computing the Yolk in Spatial Voting Games without Computing Median Lines

The yolk is an important concept in spatial voting games as it generalises the equilibrium and provides bounds on the uncovered set. We present near-linear time algorithms for computing the yolk in the spatial voting model in the plane. To the best of our knowledge our algorithm is the first algorithm that does not require precomputing the median lines and hence able to break the existing $O(n^{4/3})$ bound which equals the known upper bound on the number of median lines. We avoid this requirement by using Megiddo's parametric search, which is a powerful framework that could lead to faster algorithms for many other spatial voting problems

Catalyzed bimolecular reactions in responsive nanoreactors

We describe a general theory for surface-catalyzed bimolecular reactions in responsive nanoreactors, catalytically active nanoparticles coated by a stimuli-responsive 'gating' shell, whose permeability controls the activity of the process. We address two archetypal scenarios encountered in this system: The first, where two species diffusing from a bulk solution react at the catalyst's surface; the second where only one of the reactants diffuses from the bulk while the other one is produced at the nanoparticle surface, e.g., by light conversion. We find that in both scenarios the total catalytic rate has the same mathematical structure, once diffusion rates are properly redefined. Moreover, the diffusional fluxes of the different reactants are strongly coupled, providing a richer behavior than that arising in unimolecular reactions. We also show that in stark contrast to bulk reactions, the identification of a limiting reactant is not simply determined by the relative bulk concentrations but controlled by the nanoreactor shell permeability. Finally, we describe an application of our theory by analyzing experimental data on the reaction between hexacyanoferrate (III) and borohydride ions in responsive hydrogel-based core-shell nanoreactors.Comment: 9 pages, 4 figure

Biological aspects of little tunny Euthynnus alletteratus from Spanish and Portuguese waters.

This study provides information on some biological aspects of Euthynnus alletteratus from the western Mediterranean (Spanish coast) and in the Atlantic Ocean (south of Iberian Peninsula). A total of 1266 individuals were measured between 2003 and 2017. The L-W relationship was calculated with W equal to 0.01242 FL3.058 . Histological analysis of the ovaries and the monthly variation of the gonadosomatic index for both sexes suggested that the spawning season for Euthynnus alletteratus in the western Mediterranean Sea takes place from June to August. The lengths at first maturity (L50) were estimated to be 50.1 cm and 43.4 cm FL for female and male, respectively. Age at first maturity (A50) was calculated

Molecular Studies of Neural Tube Defect Development in the Mouse Embryo

The thesis describes studies of the development of neural tube defects (NTD) in genetically predisposed mice, specifically the curly tail and loop-tail mutants. The curly tail mouse exhibits delay or failure of closure of the neural tube at the posterior neuropore and is a model for low spinal NTD in humans. In vivo supplementation of embryos with the vitamin, inositol, significantly reduces the incidence of spinal defects raising the possibility of using inositol to prevent a proportion of NTD in humans. Moreover, inositol treatment of embryos in culture minimises the delay in posterior neuropore closure that is known, from previous studies, to lead directly to development of NTD. The mechanism of action of inositol has been examined using in vitro inhibitors and activators, measurements of inositol incorporation and analysis of gene expression in cultured embryos. The findings suggest a model that involves an increased flux through the inositol/lipid cycle which leads to activation of protein kinase C and upregulation of expression of retinoic acid receptor-β in the hindgut, the affected tissue in the curly tail mutant. The loop-tail mutant mouse is a model for craniorachischisis in humans; homozygous embryos exhibit failure of initial closure of the neural folds resulting in an open neural tube from the midbrain/hindbrain boundary along the entire body axis. Loop-tail embryos are identified by PCR analysis prior to the failure of neural tube closure. Analysis of gene expression by whole mount in situ hybridisation reveals abnormal expression of sonic hedgehog and netrin-1 in the notochord and floor plate of homozygous mutant embryos suggesting that defects in the development of these tissues may contribute to the development of NTD

Molecular genetics of chicken egg quality

Faultless quality in eggs is important in all production steps, from chicken to packaging, transportation, storage, and finally to the consumer. The egg industry (specifically transportation and packing) is interested in robustness, the consumer in safety and taste, and the chicken itself in the reproductive performance of the egg. High quality is commercially profitable, and egg quality is currently one of the key traits in breeding goals. In conventional breeding schemes, the more traits that are included in a selection index, the slower the rate of genetic progress for all the traits will be. The unveiling of the genes underlying the traits, and subsequent utilization of this genomic information in practical breeding, would enhance the selection progress, especially with traits of low inheritance, genderconfined traits, or traits which are difficult to assess. In this study, two experimental mapping populations were used to identify quantitative trait loci (QTL) of egg quality traits. A whole genome scan was conducted in both populations with different sets of microsatellite markers. Phenotypic observations of albumen quality, internal inclusions, egg taint, egg shell quality traits, and production traits during the entire production period were collected. To study the presence of QTL, a multiple marker linear regression was used. Polymorphisms found in candidate genes were used as SNP (single nucleotide polymorphism) markers to refine the map position of QTL by linkage and association. Furthermore, independent commercial egg layer lines were utilized to confirm some of the associations. Albumen quality, the incidence of internal inclusions, and egg taint were first mapped with the whole genome scan and fine-mapped with subsequent analyses. In albumen quality, two distinct QTL areas were found on chromosome 2. Vimentin, a gene maintaining the mechanical integrity of the cells, was studied as a candidate gene. Neither sequencing nor subsequent analysis using SNP within the gene in the QTL analysis suggested that variation in this gene could explain the effect on albumen thinning. The same mapping approach was used to study the incidence of internal inclusions, specifically, blood and meat spots. Linkage analysis revealed one genome-wide significant region on chromosome Z. Fine-mapping exposed that the QTL overlapped with a tight junction protein gene ZO-2, and a microsatellite marker inside the gene. Sequencing of a fragment of the gene revealed several SNPs. Two novel SNPs were found to be located in a miRNA (gga-mir-1556) within the ZO-2. MicroRNA-SNP and an exonic synonymous SNP were genotyped in the populations and showed significant association to blood and meat spots. A good congruence between the experimental population and commercial breeds was achieved both in QTL locations and in association results. As a conclusion, ZO-2 and gga-mir-1556 remained candidates for having a role in susceptibility to blood and meat spot defects across populations. This is the first report of QTL affecting blood and meat spot frequency in chicken eggs, albeit the effect explained only 2 % of the phenotypic variance. Fishy taint is a disorder, which is a characteristic of brown layer lines. Marker-trait association analyses of pooled samples indicated that egg-taint and the FMO3 gene map to chicken chromosome 8 and that the variation found by sequencing in the chicken FMO3 gene was associated with the TMA content of the egg. The missense mutation in the FMO3 changes an evolutionary, highly conserved amino acid within the FMO-characteristic motif (FATGY). In conclusion, several QTL regions affecting egg quality traits were successfully detected. Some of the QTL findings, such as albumen quality, remained at the level of wide chromosomal regions. For some QTL, a putative causative gene was indicated: miRNA gga-mir-1556 and/or its host gene ZO-2 might have a role in susceptibility to blood and meat spot defects across populations. Nonetheless, fishy taint in chicken eggs was found to be caused with a substitution within a conserved motif of the FMO3 gene. This variation has been used in a breeding program to eliminate fishy-taint defects from commercial egg layer lines. Objective The objective of this thesis was to map loci affecting economically important egg quality traits in chickens and to increase knowledge of the molecular genetics of these complex traits. The aim was to find markers linked to the egg quality traits, and finally unravel the variation in the genes underlying the phenotypic variation of internal egg quality. QTL mapping methodology was used to identify chromosomal regions affecting various production and egg quality traits (I, III, IV). Three internal egg quality traits were selected for fine-mapping (II, III, IV). Some of the results were verified in independent mapping populations and present-day commercial lines (III, IV). The ultimate objective was to find markers to be applied in commercial selection programs

Neurohormonal signaling via a sulfotransferase antagonizes insulin-like signaling to regulate a Caenorhabditis elegans stress response

Insulin and insulin-like signaling regulates a broad spectrum of growth and metabolic responses to a variety of internal and environmental stimuli. For example, the inhibition of insulin-like signaling in C. elegans mediates its response to both osmotic stress and starvation. We report that in response to osmotic stress the cytosolic sulfotransferase SSU-1 antagonizes insulin-like signaling and promotes developmental arrest. Both SSU-1 and the DAF-16 FOXO transcription factor, which is activated when insulin signaling is low, are needed to drive specific responses to reduced insulin-like signaling. We demonstrate that SSU-1 functions in a single pair of sensory neurons to control intercellular signaling via the nuclear hormone receptor NHR-1 and promote both the specific transcriptional response to osmotic stress and altered lysophosphatidylcholine metabolism. Our results show the requirement of a sulfotransferase–nuclear hormone receptor neurohormonal signaling pathway for some but not all consequences of reduced insulin-like signaling.National Center for Research Resources (U.S.)National Institutes of Health (U.S.) (grant GM024663)National Science Foundation (U.S.) (grant 1122374)University of Cambridge. Centre for Trophoblast Research (Next Generation Fellowship)National Institutes of Health (U.S.) (grant GM117408

The measurement of small ionic currents in living organisms by means of sensitive magnetometry

Recent research on developing and healing tissues suggests that small quasl-d. c Ionic currents (of magnitude 10-20/iA) may play a controlling role In the Initiation and organisation of growing tissues, but the difficulties of measuring such small currents has led to confusing results. Sensitive magnetometry provides a method of demonstrating, and, to some extent, locating such currents. A novel SQUID magnetometer system has been built and used to Investigate the magnetic fields around the uninjured human leg, and the developing chick embryo In ovo. Analysis of the magnetic fields around the human leg reveals the presence of macroscopic current loops (of magnitude up to 12/iA) within the leg. These currents are broadly similar In all subjects, and show day-to-day reproducibility In Individuals. They change predictably with time of muscle relaxation, and revert to the original signal on muscular exertion. These currents are of significance when considering the therapeutic use of Injected current for the healing of non-union in bone. The magnetic fields around eggs are detectable from day two of Incubation, and Increase In magnitude until day four or five, by which time there Is a magnetic field pattern with a null line over or near the centre of the egg. After day five the magnetic field Is reduced In size and of more complex pattern. The magnetic fields disappear If the egg Is cooled, and reappear on rewarmlng. Mathematical analysis suggests that the magnetic fields have a source deeper within the egg than the embryo Itself, probably the extra- embryonic membranes

Cryopreservation of zebrafish germ cells: technological improvements and methodological standardization for gene banking and management

Due to the increasing number of zebrafish (Danio rerio) mutant and transgenic lines, there is a high demand for assisted reproductive techniques to support facility management. Efficient zebrafish sperm cryopreservation is a pressing necessity to manage and preserve the valuable zebrafish genetic resources. Although zebrafish sperm cryopreservation was first attempted more than 30 years ago, protocols still lack standardization, which translates into high variability in post-thaw sperm quality and in vitro fertilization success. Therefore, the present thesis aims to improve the current methodologies used for zebrafish sperm cryopreservation and broodstock management towards the standardization of procedures in this species. The introductory context of the present thesis is approached in chapter 1. In this chapter the relevance of zebrafish model is discussed as well as this species sperm cryopreservation usefulness. The main factors affecting sperm quality and the application of reliable quality analysis are discussed in this chapter. The final objective of sperm cryopreservation is to obtain high quality offspring and therefore in vitro fertilization, early development and offspring quality analysis are important tools for the optimization of sperm cryopreservation methodologies. The current knowledge in sperm cryopreservation fundamentals is approached in this chapter, as well as the main advances and bottlenecks in zebrafish sperm cryopreservation. In chapter 2, the zebrafish sperm motility activation was assessed under different conditions of water temperature and conductivity. The environmental conditions present in the fertilization microenvironment are responsible for the mechanism of spermatozoa motility activation and metabolic modulation that influence the probability of fertilization success. Zebrafish is commonly reared at 28°C, but with variable water conductivity conditions among facilities. However, sperm motility analysis is routinely performed with distilled water at room temperature. We aimed to understand the effect of water temperature and conductivity on sperm motility and fertilization ability. Water at 28°C with lower water conductivity (0 and 700 μS/cm) improve sperm motility parameters. Standardization of the water conditions (of system water and activation médium used for motility analysis) among facilities is highly relevant to improve the reproducibility of sperm quality analysis and thus, to predict with higher accuracy fertilization ability. Successful cryopreservation depends on high quality sperm, which depends on the quality of breeders. Consequently, broodstock selection and management is a priority to improve sperm cryopreservation. The broodstock diet has a preponderant effect on gamete quality, particularly in phospholipids and antioxidants content which are known to promote spermatogenesis. Therefore, in chapter 3 we aimed to determine the effects of a tailor-made purified diet supplemented with phosphatidylcholine (PC) or phosphatidylethanolamine (PE) on the zebrafish reproductive performance, gamete quality and larval skeletal malformations. Both dietary supplementations with phospholipids improved sperm motility and eggs quality, however PC increased the incidence of skeletal malformations on the offspring, as previously observed in other teleosts. Although dietary phospholipids classes have a role in the ossification process of the vertebral column in teleosts, its mechanisms are still to be understood. Therefore, the development and use of a standardized diet for zebrafish broodstock is essential to reduce the variability of the reproductive performance among facilities. In chapter 4, the selection of optimal age and minimum sperm collection frequency was evaluated, since these factors are essential to obtain high quality samples. Our results indicate that young males (6-8 months) showed higher sperm quality and require a minimum of 14 days between sperm collections to recover sperm plasma membrane viability. An important bottleneck in cryopreservation is the liquid nitrogen requirement for storage. Therefore, it was established in chapter 5 a new cryopreservation method using an electric ultrafreezer (-150°C) as an alternative to liquid nitrogen, for the first time in a teleost species. This protocol reaches a fast cooling rate (-66°C/min) in one single step and yields higher sperm viability and DNA integrity in comparison to the traditional methods (-20°C/min in liquid nitrogen). The synergy obtained by the combination of cryoprotectants is a successful cryopreservation strategy that can be beneficial in the optimization of zebrafish sperm cryopreservation. Therefore, it was selected the most adequate cryoprotectant combination that generates offspring with normal skeletogenesis. Data show that 15% of DMF with 50 mM of bicine or 10% of egg yolk is beneficial for the quality of zebrafish offspring sired by cryopreserved sperm. To the best of our knowledge, this is the first report on skeletal development of zebrafish offspring sired by cryopreserved sperm performed with different extender compositions. Zebrafish is especially useful to investigate some of the most prominent human diseases such as diabetes. Among other consequences, diabetes (type I and II) causes disturbances in the male reproductive system, since glucose metabolism is an important event not only in spermatogenesis but also in mature spermatozoa metabolism. In chapter 6 we aimed to validate zebrafish as a useful model organism to investigate male reproductive dysfunctions mechanisms caused by type I diabetes. In this chapter, sperm cryopreservation was applied to a relevant zebrafish model of type I diabetes. The transgenic zebrafish under diabetic conditions shows higher levels of insulin a (insa), insulin receptor a (inra) and glucose carrier 2 (slc2a2) transcripts in spermatozoa when compared to the controls. This is because gametogenesis occurred under diabetic conditions, changing transcription in the germline. Consequently, spermatozoa carry the imprinted transcripts that will be transmitted during fertilization. Sperm quality (motility, viability and DNA integrity) was lower in the transgenic fish under (transient) diabetic state as observed in human and mouse model. Sperm cryopreservation affects sperm quality of fish both under diabetic and non-diabetic conditions. However, diabetic conditions were detrimental in sperm freezability, which can be explained by the lower initial sperm quality. In this chapter zebrafish was validated as a useful model organism to investigate male reproductive dysfunctions mechanisms caused by type I diabetes. Relevant differences between different zebrafish lines are evidenced in terms of sperm quality and susceptibility to damage, which suggests that it is an important factor to consider while establishing sperm cryopreservation protocols. This thesis offers new insights and a set of guidelines on breeder’s management and sperm cryopreservation to improve zebrafish husbandry practices. Keywords: Zebrafish, sperm quality, cryopreservation, ultrafreezer, sperm motility activation, diet, type I diabetesO peixe zebra (Danio rerio) tornou-se inquestionavelmente num dos organismos modelo mais proeminentes da atualidade, devido às suas características favoráveis para investigação. O desenvolvimento de técnicas de edição genética e a sequenciação do genoma desta espécie possibilitou o desenvolvimento de milhares de linhas transgénicas e mutantes. Consequentemente, a gestão dos numerosos genótipos trouxe desafios na manutenção de espaço e gestão destes recursos genéticos. A criopreservação de sémen é uma ferramenta valiosa para a gestão destes valiosos recursos genéticos, que pode solucionar este problema. No entanto, apesar do primeiro protocolo de criopreservação de sémen de peixe zebra ter sido desenvolvido há mais de 30 anos, ainda requer otimização e estandardização. Consequentemente, existe elevada variabilidade na qualidade do sémen e sucesso da fertilização in vitro entre biotérios. O desenvolvimento de uma técnica de criopreservação de sémen eficiente é atualmente um dos maiores desafios da comunidade de peixe zebra. O objetivo principal da presente tese foi a otimização das técnicas de gestão de reprodutores e criopreservação de sémen de peixe zebra, no sentido da estandardização das práticas e maior reprodutibilidade dos resultados científicos nesta espécie. A introdução ao contexto da presente tese é abordada no capítulo 1. Neste capitulo a importância do peixe zebra como organismo modelo é abordado assim como a utilidade da criopreservação do sémen nesta espécie. Os factores que afetam a qualidade do sémen assim como a aplicação de análises de qualidade robustas são discutidos neste capítulo. O objetivo final da criopreservação de sémen é a produção de progenia com elevada qualidade. Consequentemente, neste capítulo a fertilização in vitro, o desenvolvimento emb rionário e a análise da qualidade da progenia é discutida. Neste capítulo são explorados os fundamentos de criobiologia, principais avanços e dificuldades no desenvolvimento de protocolos de criopreservação de sémen de peixe zebra. As condições do ambiente de fertilização são responsáveis pela ativação da mobilidade dos espermatozóides e pela modulação do seu metabolismo, afetando consequentemente o sucesso da fertilização. O peixe zebra é estabulado a 28°C com parâmetros de condutividade da água variáveis entre biotérios. No entanto, as análises de mobilidade espermática são realizadas rotineiramente com água destilada a temperatura ambiente. Consequentemente, no capítulo 2 o objetivo do nosso trabalho foi caracterizar o efeito da temperatura e condutividade da água na mobilidade de sémen de peixe zebra. Adicionalmente, foi estudado o efeito da condutividade da água no sucesso da fertilização. A água a 28°C e com baixa condutividade (0 e 700 μS/cm) melhorou os parâmetros de mobilidade. A estandardização das condições da água (dos sistemas de cultivo e do meio de ativação usado na análise da mobilidade) entre biotérios é essencial para a otimização das análises de qualidade, reprodutibilidade científica e maior precisão na estimação do potencial de sucesso de fertilização de uma amostra de sémen. O sucesso da criopreservação depende da qualidade do sémen que, por sua vez, depende da qualidade dos reprodutores. Consequentemente, a seleção e gestão de reprodutores é uma prioridade, de forma a assegurar o sucesso do método de criopreservação. Um dos factores mais importantes na gestão de reprodutores é a sua dieta. A nutrição dos reprodutores tem um importante efeito na qualidade dos gametas já que afeta a gametogénese, particularmente a composição da dieta em fosfolípidos e antioxidantes. O objetivo do capítulo 3 foi determinar o efeito de dietas purificadas suplementadas com fosfatidilcolina (PC) e fosfatidiletanolamina (PE). A suplementação em fosfolípidos melhorou a mobilidade do sémen; no entanto, a suplementação em PC provocou um aumento da incidência de malformações esqueléticas na progenia. Estes resultados estão de acordo com estudos de nutrição anteriores em teleosteos. O desenvolvimento e utilização de dietas estandardizadas nos reprodutores de peixe zebra é essencial para optimizar a performance reprodutiva e reduzir a variabilidade entre biotérios. A seleção da idade ótima dos machos e a frequência mínima adequada para recolha de sémen é essencial para obter amostras com elevada qualidade. No capítulo 4 foi determinado o efeito da idade e da frequência de extração na qualidade do sémen. O nosso estudo mostrou que machos jovens (6-8 meses) de peixe zebra revelam maior qualidade de sémen e necessitam de um mínimo de 14 dias de repouso para recuperarem a viabilidade da membrana plasmática dos espermatozóides. Uma das maiores desvantagens da criopreservação é a necessidade de azoto líquido para armazenamento de amostras. Considerando esta questão, foi desenvolvido no capítulo 5 o primeiro protocolo de criopreservação de sémen de teleósteos utilizando um ultracongelador (-150°C). Este protocolo é realizado num só passo, sem a utilização de azoto líquido, sendo as amostras criopreservadas a - 66°C/min. Este protocolo melhorou a viabilidade e integridade do ADN dos espermatozóides em comparação com o método convencional (-20°C/min armazenado em azoto líquido). A combinação de diferentes crioprotetores é uma estratégia de criopreservação com elevado sucesso. Consequentemente, um dos objetivos do nosso trabalho foi selecionar a combinação de crioprotetores mais adequada para o protocolo de criopreservação estabelecido anteriormente. Os resultados deste trabalho indicam que a utilização de 15% de DMF com 50 mM de bicina ou 10% de gema de ovo produzem sémen de elevada qualidade do sémen e maior sucesso em fertilizações in vitro, assegurando também o adequado desenvolvimento esquelético da progenia. Este foi o primeiro estudo de caracterização de malformações esqueléticas desenvolvidas na progenia de peixe zebra produzido com sémen criopreservado com diferentes composições de crioprotetores. O peixe zebra é particularmente útil na investigação de doenças humanas com elevada prevalência na população mundial tal como a diabetes. Entre outras complicações geradas por esta patologia, a diabetes tipo I e II afeta o sistema reprodutor masculino. Estas perturbações ocorrem devido à alteração do metabolismo da glucose, essencial durante a espermatogénese e no metabolismo dos espermatozóides. Comparando com outros modelos, o peixe zebra tem gerações mais curtas, consequentemente seria uma ferramenta útil para esta investigação. O objetivo do capítulo 6 foi validar o peixe zebra como organismo modelo para o estudo dos mecanismos de ação da diabetes tipo I pelos quais afetam o sistema reprodutor masculino. Tal como observado em humanos e no organismo modelo de diabetes roedor, a qualidade do sémen (mobilidade, viabilidade, integridade do ADN) é reduzida na estirpe transgénica sob estado transiente de diabetes tipo I em relação ao controlo. O sémen do modelo transgénico em estado diabético revela aumento dos níveis de transcriptos de insulina a (insa), receptor de insulina a (inra) assim como de um transportador especifico de glucose GLUT 2 (slc2a2). Este facto é devido a uma alteração dos níveis de transcrição destes genes na linha germinal durante a gametogénese. O sémen criopreservado de ambos os tratamentos (controlo e diabético) revelou um decréscimo na qualidade, tal como esperado. O tratamento diabético aumentou a susceptibilidade das células à criopreservação, o que se pode dever à sua qualidade seminal inicial inferior. Assim, evidenciamos neste modelo transgénico para a diabetes tipo I os mesmos efeitos na qualidade seminal observados em humanos e em rato, validando desta forma esta linha para a investigação dos efeitos desta doença no sistema reprodutor masculino. A presente tese propõe o estabelecimento de medidas de seleção e maneio de reprodutores e análise de qualidade seminal. Adicionalmente propomos um método inovador de criopreservação de sémen, prático e económico, através do uso de um ultracongelador. Verificou-se o impacto de diferentes combinações de crioprotectores na qualidade e na esqueletogénese da progénie gerada com sémen criopreservado. Resumindo, esta tese propõe procedimentos e metodologias para a gestão de reprodutores de peixe zebra relevantes para o estabelecimento de medidas de estandardização, promovendo desta forma a reprodutibilidade de metodologias científicas.Patricia Diogo was the recipient of a doctoral grant SFRH/BD/97466/2013 from the FCT. This work was partly founded by the FCT and the European Commission (ERDF-COMPETE) through PEst-C/MAR/LA0015/2011 project and by the FCT through UID/Multi/04326/2019, and by project LARVAMIX-17925 funded by Portugal and by the European Union through FEDER, COMPETE 2020 and CRESC Algarve 2020, in the framework of Portugal 2020

Larval Fish Mortality and Vertical Chlorophyll Structures: Reexamination of the Stable Ocean Hypothesis in the Southern California Current

The natural mortality of fishes is an important component for understanding population dynamics. The larval stages of pelagic fishes living in the open ocean are particularly vulnerable to high rates of mortality, and fluctuations in these rates are thought to exert a large influence on the number of fish maturing into the spawning population. Early stage larval fishes are thought to undergo a critical period after hatching when they must find food or succumb to starvation. While the availability of suitable food for larval fishes is, on average, too low in the open ocean to support survival, patchy distributions of planktonic food can be vital habitat. The stable ocean hypothesis describes how wind mixing can influence this habitat through dilution of plankton patches and increase the mortality of larval fishes. In this dissertation, I reexamined the stable ocean hypothesis from three perspectives to understand how it might influence several key components of the California Current Ecosystem. First, I calculated larval mortality rates for five fishes (northern anchovy, Pacific sardine, Pacific hake, Pacific mackerel, and jack mackerel) from 1979 to 2015. Then I compared the mortality rates to indices of storm events and calm periods as a proxy for water column mixing and planktonic patchiness. Contrary to expectations, storm events did not negatively influence the survival of any of these species. In fact, mortality for Pacific hake decreased with an increased number of storms. Next, I examined the effect that storm events had on the vertical distribution of chlorophyll layers. I found that storms tended to decrease the occurrence of high-concentration chlorophyll layers in the water column. Finally, changes to the planktonic community composition within the chlorophyll layer was assessed. Significant variability associated with years and regions was found among sampled community compositions. Furthermore, a proxy for larval fish food exhibited considerable variability; however, the variability was not explained by the region, season, or year. Moreover, there were two peaks in biomass much higher the median value of the food proxy biomass and these events were dominated by potentially noxious algal species that may have negative implications for larval fish survival. Overall, evidence was found to support the notion that winds may influence the plankton communities larval fish rely upon, but, little support was found for a direct link to larval mortality. The stable ocean hypothesis may be important for fish recruitment in the California Current Ecosystem, but its influence appeared to be minimal on seasonal, regional, and interannual scales